nitrous oxide decomposition over fe-zsm-5 in the presence of nitric oxide: a comprehensive dft study

Nitrous Oxide Decomposition over Fe-ZSM-5 in the Presence of Nitric Oxide:A Comprehensive DFT Study

Andreas Heyden,*,†,‡ Niels Hansen,† Alexis T. Bell,*,§ and Frerich J. Keil †

Department of Chemical Engineering, Hamburg UniVersity of Technology, D-21073 Hamburg, Germany,Department of Chemistry, UniVersity of Minnesota, Minneapolis, Minnesota 55455-0431, and Department ofChemical Engineering, UniVersity of California, Berkeley, California 94720-1462

ReceiVed: May 8, 2006

A number of experimental studies have shown recently that ppm-level additions of nitric oxide (NO) enhancethe rate of nitrous oxide (N2O) decomposition catalyzed by Fe-ZSM-5 at low temperatures. In the presentwork, the NO-assisted N2O decomposition over mononuclear iron sites in Fe-ZSM-5 was studied on a molecularlevel using density functional theory (DFT) and transition-state theory. A reaction network consisting of over100 elementary reactions was considered. The structure and energies of potential-energy minima weredetermined for all stable species, as were the structures and energies of all transition states. Reactions involvingchanges in spin potential-energy surfaces were also taken into account. In the absence of NO and at temperaturesbelow 690 K, most active single iron sites (Z-[FeO]+) are poisoned by small concentrations of water in thegas phase; however, in the presence of NO, these poisoned sites are converted into a novel active iron center(Z-[FeOH]+). These latter sites are capable of promoting the dissociation of N2O into a surface oxygen atomand gas-phase N2. The surface oxygen atom is removed by reaction with NO or nitrogen dioxide (NO2). N2Odissociation is the rate-limiting step in the reaction mechanism. At higher temperatures, water desorbs frominactive iron sites and the reaction mechanism for N2O decomposition becomes independent of NO, revertingto the reaction mechanism previously reported by Heyden et al. [J. Phys. Chem. B2005, 109, 1857].

Introduction

Large amounts of nitrous oxide (N2O) are emitted fromindustrial processes used to produce nitric and adipic acid. SinceN2O is the third most important greenhouse gas following CO2

and CH4, there has been increasing interest in developingmethods for its abatement. Considerable research has shownthat N2O can be decomposed into N2 and O2 by passage overFe-ZSM-5 at elevated temperatures.1-4 One peculiarity of thetail gas streams from nitric acid plants is the presence of bothN2O and nitric oxide (NO). While most catalytic systems activefor N2O decomposition are inhibited by NO,5,6 it has beenreported that NO significantly enhances the rate of N2Odecomposition over Fe-ZSM-5. This increase in the reactionrate is especially pronounced at low temperatures (<700 K).

The positive effect of NO on N2O decomposition over Fe-ZSM-5 was first reported by Kapteijn et al.,3 who proposed thatNO in the gas phase scavenged adsorbed oxygen deposited byN2O during the oxidation of active sites, thereby leading to theformation of NO2 and regeneration of active sites. While thismechanism explains the overall increase in the N2O decomposi-tion rate due to NO, it fails to explain the observations reportedby Kogel et al.,7 Mul et al.,4 Perez-Ramı´rez et al.,8 Boutarbouchet al.,9 and Sang et al.10 who report that relatively small amountsof NO are sufficient to induce a dramatic change in the N2Odecomposition activity. Pe´rez-Ramı´rez et al.8 also observed thatfor NO/N2O feed ratios higher than 0.25 the rate of N2Odecomposition does not increase significantly, confirming thecatalytic nature of NO on N2O decomposition. Since theseauthors did not observe NO inhibition at a feed molar ratio of

NO/N2O ) 10, they suggested that NO adsorption and oxygendeposition by N2O occur at different sites in Fe-ZSM-5, andthey proposed that two neighboring Fe sites are required toaccount for NO-assisted N2O decomposition. Pe´rez-Ramı´rez etal.8,11,12 attributed the catalytic effect of NO to its action onO-atoms released during the decomposition of N2O. Theadsorbed NO2 formed in this way is proposed to react with asecond O-atom from a neighboring site, thus accelerating therecombination of oxygen from N2O and the subsequent desorp-tion of O2. The occurrence of this process was used to explainthe promotional effect of NO under the assumption that the rate-determining process in N2O decomposition is O-atom recom-bination. Recently, Sang et al.10 have observed a positive effectof NO on the rate of N2O decomposition on isolated Fe cationsin Fe-ZSM-5. This observation requires a mechanistic inter-pretation that is different from those proposed by Mul et al.4

and Pe´rez-Ramı´rez et al.8 which involve di-iron sites.While numerous investigators have studied the relationship

between the structure of Fe-ZSM-5 and its activity for N2Odecomposition, the nature of the active site and the mechanismof N2O decomposition both in the absence and in the presenceof NO are not fully understood. Both, mononuclear anddinuclear iron sites have been proposed as the principal activesite,13-36 and either N2O dissociation or O2 desorption has beensuggested as the rate-limiting step in the overall process of N2Odecomposition.37-47

Recently, we reported the results of a detailed theoreticalinvestigation of N2O decomposition occurring on mononucleariron sites in Fe-ZSM-5 in the absence of NO.21 The proposedreaction mechanism together with the rate coefficients calculatedfor each step was able to explain and reproduce various transientand steady-state experiments.22 This work showed that the rate-limiting step in N2O decomposition is N2O dissociation and thatO2 desorption is very fast.22 Isolated iron cations bound to a

* To whom correspondence should be addressed. E-mail: [email protected] (A.H.); [email protected] (A.T.B.).

† Hamburg University of Technology.‡ University of Minnesota.§ University of California, Berkeley.

17096 J. Phys. Chem. B2006,110,17096-17114

10.1021/jp062814t CCC: $33.50 © 2006 American Chemical SocietyPublished on Web 08/05/2006

single oxygen atom (viz., Z-[FeO]+) were identified as theactive sites for N2O decomposition under the reaction conditions(T > 690 K). Neighboring iron sites were not required to explainany of the experimental observations. The presence of H2O inthe feed gas was found to inhibit the rate of N2O decompositionby deactivating active sites via the process Z-[FeO]+ + H2Oh Z-[Fe(OH)2]+. Since this process is reversible, the concen-tration of active sites (Z-[FeO]+) was found to increase withincreasing reaction temperature.

The present study is an extension of our previous work andfocuses on the energetics and kinetics of the NO-assisted N2Odecomposition occurring on single iron sites in Fe-ZSM-5. Ofparticular interest is understanding the interaction of NO withZ-[FeO]+, Z-[FeO2]+, Z-[OFeO]+, and Z-[Fe(OH)2]+, theprincipal iron-containing species identified in our earlier studyof N2O decomposition in the absence of NO.21,22 It is shownthat such interactions can lead to the formation of iron hydroxo,nitrite,andnitratespecies,Z-[FeOH]+,Z-[FeONO]+,Z-[FeO2N]+,and Z-[FeO2NO]+, and that this opens up new pathways forN2O decomposition at temperatures below 700 K. The presentinvestigation also illustrates how the nature of the active sitescan change with temperature, both in the presence and in theabsence of NO. Yet another objective of this study was toexamine how NO might be formed directly from N2O at lowtemperatures. This part of the work was motivated by thespectroscopic results of Chen et al.,48 Grubert et al.,49 El-Malkiet al.,50 and the experimental observations of Sang and Lund,51,52

Kiwi-Minsker et al.,46,53 and Novakova and Sobalı´k,54 whosuggested that NO might be formed on the catalyst from N2Oin the absence of NO in the feed stream.

We report here the results of theoretical calculations for alarge number of elementary processes that are envisioned tooccur during N2O decomposition on isolated mononuclear Fesites in Fe-ZSM-5 in the presence of NO. In a companion paper,we use the calculated rate parameters of the present study tosimulate the effects of NO on N2O decomposition under bothsteady-state and non-steady-state conditions.

TheoryThe catalytically active center and a portion of the zeolite

framework are represented by a 23-27 atom cluster. This modelis identical to that used in our earlier work.21 As shown in Figure1, the portion of the cluster describing the zeolite contains anAl-atom in the T12 position of the framework surrounded byshells of O- and Si-atoms. The terminal Si-atoms are fixed in

their crystallographic positions, as reported by Olson et al.55

Dangling bonds are terminated by H-atoms located 1.48 Å fromeach terminal Si-atom oriented in the direction of the nextO-atom in the zeolite matrix. This corresponds to the Si-Hdistance in SiH4. Heyden23 has demonstrated that extendedcharge transfer occurs to a very limited extend over the zeolitematrix, so that the constrained T5 cluster model used in thiswork gives reliable results for electronic energy differences. Tostudy the influence of nitric oxide on the active iron site, theanionic cluster is charge-compensated by a metal hydroxo,nitrite, or nitrate species, [FeOH]+, [FeONO]+, [FeO2N]+, or[FeO2NO]+, placed between two of the four O-atoms surround-ing the Al-atom (see Figure 1).

Quantum chemical calculations of the geometry and energiesof potential-energy minima were performed for spin surfaceswith spin multiplicities ofMS ) 2-8, using gradient-correctedspin density functional theory (DFT). To represent the effectsof exchange and correlation, Becke’s three-parameter exchangefunctional and the correlation functional of Lee, Yang, and Parr(B3LYP)56 were used with a very fine numerical grid size(m5).57 The B3LYP functional has proven to be effective for anumber of reactions involving iron oxide molecules, leadingus to conclude that a DFT-B3LYP approach can also be usedsuccessfully to investigate N2O decomposition on isolated Fesites present in Fe-ZSM-5.58-62 To speed up the calculation ofpotential-energy minima, all structures were preoptimized withthe pure density functional BP8663,64 using the resolution ofidentity (RI) approach for computing the electronic Coulombinteraction.65,66Basis sets at the triple-ú level with polarizationfunctions (TZVP)67 were used for all atoms, including iron.Heyden23 has demonstrated that, for the TZVP basis set, relativeelectronic energies are converged with respect to the basis setsize. No corrections were made for the basis set superpositionerror (BSSE).68,69 All calculations were carried out using theTURBOMOLE V5.7 suite of programs70,71 in C1 symmetry.

Calculations on different spin potential-energy surfaces(PESs) revealed that the energy difference between differentspin surfaces is usually significant so that only energies of PESminima for the ground state are reported. To approximateelementary reaction rates, first-order saddle points and minimaon the seam of two PESs had to be determined. Saddle-pointstructures were determined only for the spin PES on which bothreactant and product states have the lowest electronic energy.Likewise, minimum energy structures on the seam of two PESswere only determined for the two lowest spin PESs if thereactant and product state had ground electronic states ondifferent spin PESs. Spin contamination was negligible forground-state minimum structures. Some spin contamination wasobserved for transition states and minimum structures on a seamof two PESs. Nevertheless, in all cases, it was possible todistinguish clearly between states of different spin multiplicities.

Minimizations of the constrained cluster were performed inCartesian coordinates with an energy convergence criterion ofat least 10-7 Ha and a gradient norm convergence criterion of10-4 Ha/bohr. At the end of all minimizations or saddle-pointsearches, a frequency calculation was done to confirm that allfrequencies are positive for minima and only one frequency isimaginary for saddle points.

To accelerate the search for transition states, a combinationof interpolation and local methods was used. The growing-stringmethod72 was used in mass-weighted coordinates with amaximum of 13-16 nodes. After the two ends of the growingstring joined, the growing-string method was terminated andan approximate saddle point was obtained. To refine the positionof the saddle point, the modified dimer method73 was employed.A convergence criterion of the gradient norm of 5× 10-4 Ha/bohr was used for transition states.

Figure 1. Iron nitrite, nitrate, and hydroxo zeolite cluster. Structuresare potential-energy minima on the potential-energy surface with a spinmultiplicity of MS ) 5. Atomic distances are indicated in angstroms.

N2O Decomposition over Fe-ZSM-5 J. Phys. Chem. B, Vol. 110, No. 34, 200617097

Minimum potential-energy structures on the seam of twoPESs were determined with a multiplier penalty functionalgorithm (see Heyden et al.21 and Heyden23 for details).Converged minimum energy crossing point structures had amaximum energy difference on both PESs of less than 10-6

Ha.Overall equilibrium constants and reaction rate constants were

computed using standard statistical mechanics and absolute ratetheory.74 We used the harmonic approximation, and includedthe contributions of the translational, rotational, vibrational, andelectronic partition functions of all gaseous species participatingin the reaction and the vibrational and electronic contributionof the zeolite cluster. Since the zeolite cluster is part of a solid,translational and rotational partition functions for the zeolitewere assumed to be equal in the reactant and transition state.To calculate rates of spin-surface crossing, for example,desorption rates of oxygen, absolute rate theory was used underthe assumption that the partition functions of the hypotheticaltransition state (minimum on the seam of two PESs) and theminimum on the PES with lower spin multiplicity (adsorbedstate) are identical except for the electronic energy. Thisprocedure completely neglects a low spin-surface crossingprobability. To estimate if very low spin-surface crossingprobabilities could have a significant effect on the reaction rateconstants, thermally averaged spin transition probabilities arecalculated with the Landau-Zener formula,75 using a spin-orbit coupling energy,H12, of 395 and 825 J/mol, as calculatedby Danovich and Shaik76 for the oxidative activation of H2 byFeO+. Additional details concerning the calculations of rateparameters and the estimation of errors can be found in refs 21and 23.

It is important to note that the necessary correction for thereaction rates to account for a spin-inversion probability smallerthan 1 is comparable to the error inherent in the DFTcalculations of activation energies. In addition, the rates of spin-surface crossing were never rate limiting in this work and, hence,spin-surface crossing should not have an influence on the overallkinetics of the reaction network studied.

Results and DiscussionMost explanations of the promotional effect of NO on the

N2O decomposition over Fe-ZSM-5 are based on the assumptionthat NO adsorbs on an iron oxide species, that is, that it interactswith the same iron species responsible for N2O decompositionin the absence of NO. Our recent theoretical work has shownthat iron oxide species can indeed serve as the active speciesfor temperatures above 700 K and in the absence of NO.21,22

However, below this temperature, the majority of the iron sitesare poisoned by water in the feed via the process Z-[FeO]+ +H2O h Z-[Fe(OH)2]+ and our work has shown that the iron-dihydroxide species are inactive for N2O decomposition.21

As noted in the Introduction, the promotional effect of NOon N2O decomposition is especially pronounced at low tem-peratures (T < 700 K) (where iron-dihydroxide species arecalculated to be the majority iron species in the absence of NO)and disappears at high temperatures (where iron oxide speciesare calculated to be the majority iron species in the absence ofNO). As a result, an explanation for NO-assisted N2O decom-position that is based on the assumption that NO interacts withiron oxide species seems improbable. An alternative explanationis that NO converts the catalytically inactive iron-dihydroxidespecies into active species. In what follows, we first presentcalculations showing how NO can convert catalytically inactiveZ-[Fe(OH)2]+ into catalytically active Z-[FeOH]+ sites. Second,we present a reaction mechanism for N2O decompositionutilizing Z-[FeOH]+ sites. Third, we show that while NO caninteract with iron oxide species at low temperatures to formvarious iron nitrite and nitrate species, these species do not

contribute significantly to N2O decomposition either in thepresence or absence of NO. Fourth, we examine severalpathways for the formation of NO from N2O on single ironsites. All quantum chemical calculations are summarized inTable 1 of the Appendix. Thermally averaged Landau-Zenertransition probabilities are summarized for spin-orbit couplingenergies of 395 and 825 J/mol for several temperatures in Table2 of the Appendix. Failure to correct reaction rates for spin-inversion probabilities smaller than 1 creates errors smaller thanan error in the activation barrier of 4 kcal/mol (at 700 K).

Activation of Z -[Fe(OH)2]+ Sites. Figure 2 illustrates amechanism by which NO converts Z-[Fe(OH)2]+ sites intoZ-[FeOH]+ sites, which Nobukawa et al.77 have proposedrecently to be active for selective catalytic reduction of N2Owith CH4 in Fe-BEA zeolites. Nitric oxide can adsorb from theN-end on the septet spin PES with an enthalpy of adsorption of∆Hads) -0.9 kcal/mol (averaged from 600 to 800 K) and∆Hads

) 1.1 kcal/mol for N2O adsorption from the O-end. There is anegligible spin-change barrier of 0.1 kcal/mol from Z-[Fe(OH)2]+-(NO){MS ) 7} to Z-[Fe(OH)2]+(NO){MS ) 5} sites. The spin-change process involves an enthalpy change of∆HR ) -0.01kcal/mol. Once adsorbed on the quintet PES, NO interacts withone hydroxo group to form adsorbedcis- or trans-HNO2. Thetransition state is characterized by a N-O distance of the N-atomfrom the nitric oxide and one O-atom from one of the hydroxogroups on the Fe-atom of 1.87 Å for the formation oftrans-HNO2 and 1.75 Å for the formation ofcis-HNO2. The Fe-OHbond length increases in the transition state from 1.80 to 1.97Å (trans-HNO2) or 2.05 Å (cis-HNO2). The activation barrierfor the formation of HNO2 is Eq ) 9.7 kcal/mol (trans-HNO2)or Eq ) 11.0 kcal/mol (cis-HNO2). The imaginary frequencyassociated with the transition-state mode is 196i cm-1 (trans-HNO2) or 101i cm-1 (cis-HNO2). The enthalpy of reaction is∆HR(trans-HNO2) ) 6.4 kcal/mol or∆HR(cis-HNO2) ) 8.7kcal/mol,respectively.HNO2desorbsreadilyfromZ-[FeOH]+(HNO2)sites to form mono-hydroxo-Fe sites. The enthalpy of desorptionis ∆HR(trans-HNO2) ) 5.9 kcal/mol or∆HR(cis-HNO2) ) 4.3kcal/mol. Thus, in the presence of NO (and the absence of largeamounts of HNO2), Z-[FeOH]+ species can be formed readilyfrom Z-[Fe(OH)2]+ sites.

N2O Decomposition on Z-[FeOH]+ Sites. Figure 3 il-lustrates the catalytic cycle for N2O decomposition on Z-[FeOH]+

Figure 2. Activation of poisoned Z-[Fe(OH)2]+{MS ) 6} sites. Allenergies are zero-point corrected, in kcal/mol and with reference toZ-[Fe(OH)2]+ with the appropriate amounts of NO,trans-HNO2, andcis-HNO2. The numbers in parentheses correspond tocis-HNO2.Energies of potential-energy minima are in black. Energies of transitionstates are in red. Energies of minima on the seam of two PESs are ingreen. Black structures are on the PES withMS ) 5. Green structuresare on the PES withMS ) 6. Structures in blue are on the PES withMS ) 7.

17098 J. Phys. Chem. B, Vol. 110, No. 34, 2006 Heyden et al.

sites. N2O adsorbs through the N-end with an enthalpy ofadsorption of∆Hads ) -1.4 kcal/mol and through the O-endwith an enthalpy of adsorption of∆Hads) -1.8 kcal/mol. Thetransition state for the reaction of Z-[FeOH]+(ON2) to formZ-[OFeOH]+ and N2 is characterized by a bending of the N2Omolecule from 180° in the adsorbed state to 137.4° in thetransition state, whereas the length of the N′-O′′ bond of theN2O molecule increases from 1.20 to 1.38 Å. The activationbarrier for the decomposition isEq ) 24.0 kcal/mol. Theimaginary frequency associated with the transition-state modeis 473i cm-1. Because the enthalpy of reaction is moderatelyexothermic,∆HR ) -16.1 kcal/mol, the reverse reaction has asignificant barrier and should not occur readily. Z-[OFeOH]+

sites are possible active sites for the N2O dissociation. N2Oadsorbs on Z-[OFeOH]+ centers through the N-end with anenthalpy of adsorption of∆Hads ) -0.8 kcal/mol and throughthe O-end with an enthalpy of adsorption of∆Hads) -1.5 kcal/mol. Hardly any N2O can be expected to adsorb on Z-[OFeOH]+

sites under reaction conditions. The transition state for thereaction of Z-[OFeOH]+(ON2) to form Z-[O2FeOH]+ and N2

is characterized by a bending of the N2O molecule from 180°in the adsorbed state to 136.8° in the transition state, whereasthe length of the N′-O′′ bond of the N2O molecule increasesfrom 1.20 to 1.34 Å. The O-atom from N2O forms a bond withthe lone oxygen atom from Z-[OFeOH]+. The Fe-O bondincreases along the reaction coordinate from 1.62 to 1.83 Å inthe transition state. The O-O bond length is 1.59 Å. Theactivation barrier for N2O decomposition isEq ) 46.5 kcal/

mol. The imaginary frequency associated with the transition-state mode is 710i cm-1. Because the enthalpy of reaction is∆HR ) -20.5 kcal/mol, the reverse reaction has an even higherbarrier and should not occur. Z-[O2FeOH]+ species are morestable on the septet PES than on the quintet PES. A negligiblespin-change barrier of aboutEq ) 6.0 kcal/mol was found forthe spin-inversion process. The enthalpy of reaction is∆HR )-4.5 kcal/mol, suggesting that Z-[O2FeOH]+ species on thequintet and septet PES are in equilibrium. Z-[O2FeOH]+{MS

) 7} species consist of a superoxide O2- anion and a OH group

associated with an Fe3+ cation. The Fe-O bond distance ofthe superoxide anion to the iron cation is 2.06 Å. The O-Obond distance is 1.31 Å, and the O-O vibrational frequency is1202 cm-1, confirming the superoxide character of the twoadsorbed O-atoms.78 Oxygen can desorb from Z-[O2FeOH]+{MS

) 7}. The O2 desorption barrier isEq ) 7.6 kcal/mol, and theenthalpy of desorption is∆Hdes) 5.8 kcal/mol. The imaginaryfrequency associated with the transition-state mode is 58i cm-1.As in all catalytic cycles reported in this study, O2 desorptionis fast and, hence, oxygen inhibition is not projected to occur.

The highest barrier in the catalytic cycle involving Z-[FeOH]+

sites is the second N2O decomposition on Z-[OFeOH]+, whichhas an activation barrier of over 43 kcal/mol with respect tothe gas phase, making this catalytic cycle unlikely to occurexcept at elevated temperatures. The second N2O dissociationbarrier on Z-[OFeO]+/Z-[FeO2]+ sites was previously calcu-lated to be 12 and 17.3 kcal/mol, respectively.21 The reasonthat the second N2O dissociation barrier on Z-[OFeOH]+ issignificantly higher than that on Z-[OFeO]+ or Z-[FeO2]+ isbecause superoxide species cannot be formed on Z-[OFeOH]+

before the third oxygen atom is loaded on the iron atom, as ispossible on Z-[OFeO]+ or Z-[FeO2]+ sites.

Figure 3 illustrates alternative reaction pathways for complet-ing the catalytic cycle in the presence of NO. To bypass thesecond N2O dissociation on Z-[OFeOH]+ sites, NO can adsorbon Z-[OFeOH]+ sites, forming Z-[ONOFeOH]+ species. NO2can then desorb from these species. The enthalpy of NOadsorption is∆Hads ) -31.6 kcal/mol. The enthalpy of NO2desorption is∆Hdes) 16.8 kcal/mol. The highest barrier in thiscatalytic cycle is the N2O decomposition,Eq ) 24.0 kcal/mol,suggesting a fast reaction mechanism in the presence of NO.This catalytic cycle involves the dissociation of one N2Omolecule and the consumption of one NO molecule (one NO2

molecule and one N2 molecule are formed). Considering thathigh N2O conversion rates can be achieved over Fe-ZSM-5 atlow temperatures in the presence of small amounts of NO andthat significant amounts of O2 are observed experimentallyduring N2O decomposition, NO2 should be able to interact withZ-[OFeOH]+ sites.

A reaction pathway that bypasses N2O decomposition onZ-[OFeOH]+ sites and involves dissociation of one N2Omolecule, consumption of one NO2 molecule, and productionof one NO, O2, and N2 molecule is illustrated in Figure 3. NO2adsorption on Z-[OFeOH]+ sites involves surmounting a smallbarrier ofEq ) 6.9 kcal/mol. The enthalpy of adsorption is∆Hads

) -1.4 kcal/mol. The imaginary frequency associated with thetransition-state mode is 400i cm-1. The transition state ischaracterized by a O-O bond distance of 1.84 Å. In theZ-[HOFeO]+(NO2) adsorption complex, the O-O bond lengthis 1.40 Å and the N-O bond length increases to 1.53 Å. NOcanreadilydesorbfromZ-[HOFeO]+(NO2)toformZ-[O2FeOH]+.Oxygen can desorb from Z-[O2FeOH]+, as described above.The net effect of both catalytic cycles is the dissociation of N2Omolecules into N2 and O2, thereby bypassing the dissociationof N2O on Z-[OFeOH]+ sites.

In principle, NO and HNO2 formed in situ can also interactwith the hydroxyl group on Z-[OFeOH]+ to form HNO2 or NO2

Figure 3. Catalytic cycle of the N2O dissociation on mononuclearZ-[FeOH]+{MS ) 5} sites. All energies are zero-point corrected, inkcal/mol and with reference to Z-[FeOH]+ with the appropriate amountsof N2O, N2, O2, NO, and NO2. Energies of potential-energy minimaare in black. Energies of transition states are in red. Energies of minimaon the seam of two PESs are in green. Black structures are on the PESwith MS ) 5. Structures in green are on the PES withMS ) 6. Structuresin blue are on the PES withMS ) 7. Multiple numbers under a PESminimum structure correspond to different catalytic cycles (see Table1).


and H2O and a catalytically active Z-[FeO]+ site. Figure 4illustrates these reaction pathways and shows that these pro-cesses are endothermic and should therefore not be favored overthose processes involving NO or NO2 reaction with the oxygenatom in Z-[OFeOH]+. As a result, these pathways are notdiscussed further.

To summarize, in the absence of NO and at temperaturesbelow 650 K, the majority of the active sites in Fe-ZSM-5 arein the form of Z-[Fe(OH)2]+. The zero-point corrected energybarrier for water to desorb and to form catalytically activeZ-[FeO]+ sites is about 44.5 kcal/mol. Owing to the entropygain in desorbing a water molecule, this process occurs at hightemperatures but does not occur at low temperatures (<650 K).If NO is present in the gas stream and in contact with Fe-ZSM-5, the zero-point corrected energy barrier for the formation ofactive Z-[FeOH]+ sites is about 13.3 kcal/mol, which issignificantly lower than the activation barrier for the desorptionof H2O from Z-[Fe(OH)2]+. As a result, if large amounts ofnitric oxide are added to an Fe-ZSM-5 catalyst at low temper-atures, as done by Bulushev et al.,79 the catalyst is activatedimmediately. Active Z-[FeOH]+ sites are formed much morerapidly than active Z-[FeO]+ species. The highest barrier forN2O decomposition on Z-[FeOH]+ is 20.5 kcal/mol with respectto the gas phase, which is about 3.5 kcal/mol lower than theactivation barrier for N2O decomposition on Z-[FeO]+ sites.On the other hand, at elevated temperatures (>700 K), waterdesorption becomes the dominant process for activatingZ-[Fe(OH)2]+ sites. No net gas species are formed in the processof producing Z-[FeOH]+ sites, so that at high temperatures theentropy increase associated with desorption of H2O should offsetthe higher activation barrier for the water desorption process,Z-[Fe(OH)2]+ h Z-[FeO]+ + H2O.

Interaction of NO with Z -[FeO]+, Z-[FeO2]+, andZ-[OFeO]+ Sites. At elevated temperatures (T > 700 K),

isolated Fe cations are predicted to be present primarily asZ-[FeO]+, Z-[FeO2]+, and Z-[OFeO]+ sites.21,22 In whatfollows, the interaction of these iron oxide species with NO toform iron nitrite and nitrate species is investigated. The purposeof this section is to show that NO has very little effect on theoverall N2O decomposition activity of single iron sites in Fe-ZSM-5 at temperatures where iron nitrite and nitrate speciesmight be formed.

Figure 5 illustrates the interaction of NO with Z-[FeO]+ sites.Nitric oxide adsorbs on Z-[FeO]+ centers from the nitrogenend with an enthalpy of adsorption of∆Hads) -32.9 kcal/mol(averaged over 600-800 K), forming Z-[FeONO]+ species.During the adsorption process, spin pairing occurs. The groundstate of Z-[FeO]+ is on the sextet PES, whereas the groundstate of Z-[FeONO]+ is on the quintet PES. The adsorptionprocess involves a negligible spin-change barrier of∼1.1 kcal/mol. The bonding of Z-[FeONO]+ is illustrated in Figure 1,the Fe-O bond increases during the adsorption process from1.66 to 1.84 Å. The O-N′-O′′ bond angle is calculated to be112.9° in the adsorbed state on the PES with a spin multiplicityof MS ) 5. The characteristic vibrational frequency of adsorbednitric oxide is calculated to be 1701 cm-1. In principle, nitrogendioxide can desorb from Z-[FeONO]+; however, the enthalpyof desorption for this process is∆Hdes) 66.0 kcal/mol, makingthis process unlikely to occur.

A second potential-energy minimum was found for adsorbedNO, Z-[FeO2N]+, illustrated in Figures 1 and 5. The enthalpyof adsorption was calculated to be∆Hads ) -37.8 kcal/mol.The adsorption process involves a spin-change barrier of 1.4kcal/mol. The reason for the difference in the spin-changebarriers for the formation of Z-[FeONO]+ and Z-[FeO2N]+ isattributable to the assumption that the zero-point energies ofthe adsorbed state and transition state are equivalent. The Fe-Obond length in Z-[FeO2N]+ is 2.11 Å, and the O-N′-O′′ bondangle is 111.3°. The characteristic vibrational frequencies ofadsorbed nitric oxide are 1238 and 1330 cm-1. The enthalpyof NO2 desorption from Z-[FeO2N]+ is ∆Hdes ) 70.9 kcal/mol, making NO2 desorption very unlikely to occur.

Figure 4. Two pathways from Z-[OFeOH]+ sites to active Z-[FeO]+{MS

) 6} sites. All energies are zero-point corrected, in kcal/mol and withreference to Z-[OFeOH]+ with the appropriate amounts of H2O, trans-HNO2, NO, and NO2. Energies of potential-energy minima are in black.Energies of transition states are in red. Energies of minima on the seamof two PESs are in green. Black structures are on the PES withMS )5. Structures in green are on the PES withMS ) 6. Structures in blueare on the PES withMS ) 7.

Figure 5. Interaction of nitric oxide with Z-[FeO]+{MS ) 6} sites.All energies are zero-point corrected, in kcal/mol and with referenceto Z-[FeO]+{MS ) 6}. Energies of potential-energy minima are inblack. Energies of minima on the seam of two PESs are in green.Structures in green are on the PES withMS ) 6. Black structures areon the PES withMS ) 5. Structures in magenta are on the PES withMS ) 4.


Nitric oxide might also adsorb on Z-[FeO]+ from the nitrogenend of the molecule. The enthalpy of adsorption for this processis calculated to be∆Hads) -13.6 kcal/mol, a value significantlylower than that for the formation of Z-[FeONO]+ andZ-[FeO2N]+ species. Adsorption of NO through the nitrogenend of the molecule involves surmounting a negligible spin-change barrier of 0.2 kcal/mol. The N′-O′ bond length is 1.15Å and is essentially the same as that for gaseous NO. Thecharacteristic harmonic vibrational frequency of adsorbed nitricoxide is calculated to be 1895 cm-1, in good agreement withthe experimental values of 1884 and 1874 cm-1 reported byMul et al.4 Owing to the low adsorption enthalpy,-13.6 kcal/mol, Z-[OFeNO]+ species (or similar ones) are unlikely to playa role in N2O decomposition at reaction temperatures above500 K. Therefore, iron species on which NO is weakly adsorbedthrough the N-end are not discussed further. No other, morestable, potential-energy minimum with a nitrogen atom in directcontact with the iron atom was found in this study.

Figure 6 illustrates the interaction of NO with Z-[FeO2]+

and Z-[OFeO]+ sites. Simulations of N2O decomposition onFe-ZSM-5 reveal that Z-[FeO2]+ and Z-[OFeO]+ are alwaysin equilibrium. While Z-[FeO2]+ is the more abundant species,

Z-[OFeO]+ is the more active center for N2O decomposition.Nitric oxide adsorbs from the N-end with an enthalpy ofadsorption of∆Hads ) -9.0 kcal/mol on Z-[FeO2]+ centers,forming Z-[FeOONO]+ sites. The spin-change barrier foradsorption in this manner is 6.3 kcal/mol, suggesting a fast NOadsorption process. Nitrogen dioxide readily desorbs fromZ-[FeOONO]+. The spin-change barrier from the quintet PESback to the sextet PES of the active site is below the zero-pointcorrected energy of Z-[FeO]+ and NO2. The enthalpy ofdesorption averaged over 600-800 K is calculated to be∆Hdes

) 1.0 kcal/mol. As a result, in the presence of NO, Z-[FeO2]+

sites are rapidly reduced to Z-[FeO]+.Our results for the reaction Z-[FeO2]+ + NO h Z-[FeO]+

+ NO2 can be compared with those of Sang et al.10 Theseauthors reported a change in electronic energy for this reactionof about-1.5 kcal/mol, a number in reasonable agreement withthe zero-point corrected energy difference of-6.6 kcal/molcalculated in this work. The differences between the calculatedvalues are attributable to the use of a cluster located in the T1position by Sang et al.10 rather than the T12 position used inthis work and the use of a double-ú basis set (LACVP**) ratherthan a triple-ú basis set.

Nitric oxide can also adsorb on Z-[OFeO]+ sites to formZ-[OFeONO]+ or Z-[OFeO2N]+ species. The spin-changebarrier for adsorption is 3.7 or 4.6 kcal/mol, respectively,suggesting that the adsorption process is fast. The correspondingenthalpies of adsorption are∆Hads) -30.5 kcal/mol and∆Hads

) -34.0 kcal/mol, respectively. The characteristic harmonicvibrational frequency of adsorbed nitric oxide on Z-[OFeO]+

sites is calculated to be 1797 cm-1 for Z-[OFeONO]+ and 1256and 1308 cm-1 for Z-[OFeO2N]+. Nitrogen dioxide can desorbfrom Z-[OFeONO]+ and Z-[OFeO2N]+. The desorption barrieris 16.0 kcal/mol from Z-[OFeONO]+ sites and 19.2 kcal/molfrom Z-[OFeO2N]+ sites, suggesting that NO2 desorption shouldbe fast at reaction temperatures. The enthalpy of desorption is∆Hdes) 14.4 kcal/mol from Z-[OFeONO]+ sites and∆Hdes)17.9 kcal/mol from Z-[OFeO2N]+ centers. Consequently,Z-[OFeO]+ sites are reduced rapidly in the presence of NO toZ-[FeO]+.

Nitric oxide can also adsorb on Z-[OFeO]+ sites to formstable iron nitrate species, Z-[FeO2NO]+. The spin-changebarrier for adsorption is 5.8 kcal/mol, and the enthalpy ofadsorption is∆Hads ) -58.3 kcal/mol. The desorption barrieris 63.2 kcal/mol, suggesting that iron nitrate species once formedwill be difficult to eliminate. The bonding of Z-[FeO2NO]+ isillustrated in Figure 1; the Fe-O bond increases during theadsorption process from 1.68 Å in Z-[OFeO]+ to 2.08 Å in theiron nitrate species. The characteristic harmonic vibrationalfrequency of adsorbed NO in Z-[FeO2NO]+ is calculated to be1641 cm-1. Mul et al.4 and Pe´rez-Ramı´rez et al.11 observed asharp infrared band at 1635 and 1632 cm-1, respectively,suggesting that iron nitrate species might be formed during N2Odecomposition on Fe-ZSM-5. Nitrogen dioxide can desorb fromZ-[FeO2NO]+ sites with an activation barrier of 44.2 kcal/mol,which is equal to the enthalpy of NO2 desorption. The spin-change barrier for NO2 adsorption on Z-[FeO]+ sites is 1.8 kcal/mol.

Nitrogen dioxide adsorption on Z-[OFeO]+ sites was alsoconsidered. The adsorption process involves spin pairing andsubsequent surmounting of a small activation barrier ofEq )6.6 kcal/mol on the quintet PES. The enthalpy of adsorption is∆Hads ) -2.0 kcal/mol. The imaginary frequency associatedwith the transition-state mode is 510i cm-1. The transition stateis characterized by an O-O bond distance of 1.79 Å (oneoxygen bond to Fe, the other oxygen bond to N) and a slightelongation of the N-O bond length to 1.22 Å. Nitric oxide candesorb from Z-[OFeO]+(NO2) sites to form Z-[OFeO2]+

Figure 6. Interaction of nitric oxide with Z-[FeO2]+{MS ) 6} andZ-[OFeO]+{MS ) 6} sites. All energies are zero-point corrected, inkcal/mol and with reference to Z-[FeO2]+ or Z-[OFeO]+. Energies ofpotential-energy minima are in black. Energies of minima on the seamof two PESs are in green. Structures in green are on the PES withMS

) 6. Black structures are on the PES withMS ) 5. Structures in magentaare on the PES withMS ) 4.


species. The desorption barrier for this process is 12.0 kcal/mol. The enthalpy of desorption at reaction temperature is∆Hdes

) 12.2 kcal/mol. Since O2 can readily desorb from Z-[OFeO2]+

species (see Heyden et al.21), the reduction of Z-[OFeO]+ siteswith NO2 is a fast, entropy driven process (two gas moleculesare produced from one NO2 molecule).

To summarize, exposure of Z-[FeO]+, Z-[FeO2]+, andZ-[OFeO]+ sites to NO leads to the formation of three newstable species, Z-[FeONO]+, Z-[FeO2N]+, and Z-[FeO2NO]+.The enthalpy of desorption of NO or NO2 from these sites is∆Hdes ) 32.9, 37.8, and 42.2 kcal/mol, respectively. Theseresults suggest that if iron oxide species were present in Fe-ZSM-5 at low temperatures, small amounts of nitric oxide inthe feed gas of the N2O decomposition would result in theformation of significant amounts of Z-[FeONO]+, Z-[FeO2N]+,

and Z-[FeO2NO]+ species. However, our earlier work on thesimulation of N2O decomposition on isolated Fe sites in Fe-ZSM-5 indicates that iron oxide species will not be present atlow temperatures (<650 K) because such sites will react veryrapidly with H2O to form Z-[Fe(OH)2]+ sites. Therefore, ironnitrite and nitrate species can only be formed at highertemperatures where water desorbs. The enthalpy of waterdesorption,∆Hdes) 43.4 kcal/mol (Z-[Fe(OH)2]+ h Z-[FeO]+

+ H2O), is higher than the enthalpy of NOx desorption fromiron nitrite or nitrate species. As a result, NOx desorption beginsat lower temperatures than H2O desorption, and large amountsof nitric oxide are necessary to displace H2O at lower temper-atures or to form iron nitrite or nitrate species at highertemperatures.

Figures 7-12 illustrate the catalytic cycle of the N2Odecomposition on iron nitrite and nitrate species. The reactionmechanism, reaction intermediates, and transition states are verysimilar to those shown for N2O decomposition on Z-[FeOH]+

species (see Figure 3). As a result, these pathways are notdiscussed further. More information about these reactionpathways can be found in ref 23.

In industrial tail gases, the H2O concentration is significantlylarger than the NOx concentration.80 As a result, iron nitrite andnitrate species should not be present under industrial conditions.In some experimental studies,79 the NOx concentration is verylarge so that iron nitrite and nitrate species might contribute tothe N2O decomposition. On iron nitrite and nitrate species, thefirst N2O dissociation barrier with respect to the gas phase iscalculated to be 21.5, 21.2, and 22.4 kcal/mol, respectively. Thiselementary reaction step is the rate-limiting step in the reaction

Figure 7. Catalytic cycle of the N2O dissociation on mononuclearZ-[FeONO]+{MS ) 5} sites. All energies are zero-point corrected, inkcal/mol and with reference to Z-[FeONO]+ with the appropriateamounts of N2O, N2, O2, NO, and NO2. Energies of potential-energyminima are in black. Energies of transition states are in red. Energiesof minima on the seam of two PESs are in green. Black structures areon the PES withMS ) 5. Green structures are on the PES withMS )6. Structures in blue are on the PES withMS ) 7. Multiple numbersunder a PES minimum structure correspond to different catalytic cycles(see Table 1).

Figure 8. Alternative catalytic cycle of the N2O dissociation onmononuclear Z-[FeONO]+{MS ) 5} sites. All energies are zero-pointcorrected, in kcal/mol and with reference to Z-[FeONO]+ with theappropriate amounts of N2O, N2, O2, NO, and NO2. Energies ofpotential-energy minima are in black. Energies of transition states arein red. Energies of minima on the seam of two PESs are in green.Black structures are on the PES withMS ) 5. Structures in green areon the PES withMS ) 6.


mechanism of the NO-assisted N2O decomposition on ironnitrite and nitrate species. On Z-[FeOH]+ species, we calculatedin this study a rate-limiting barrier of 20.5 kcal/mol, and forZ-[FeO]+ sites, Heyden et al.21 computed an only marginallylarger barrier of 24-24.3 kcal/mol. As a result, iron nitrite andnitrate species are not more active than Z-[FeOH]+ andZ-[FeO]+ species and large amounts of nitric oxide cannotsignificantly increase the N2O decomposition rate.

Formation of NO from N 2O. El-Malki et al.,50 Bulushev etal.,79 Kiwi-Minsker et al.,46,53 Sang and Lund,51,52 and Nova-kovaand Sobalı´k54 have proposed that NO formed from N2Ocould facilitate the decomposition of N2O at low temperaturesin the absence of NO in the feed. Figure 13 illustrates reactionpathwaysfor theformationofNOonZ-[OFeO]+,Z-[ONOFeO]+,Z-[OFeO2N]+, Z-[OFeO2NO]+, and Z-[OFeOH]+. Since thesepathways are very similar, we will only discuss that for the

formation of NO on Z-[OFeO]+ sites. Nitrous oxide interactsvia the N-end with the O-atom on the mononuclear iron siteand forms an adsorbed NO dimer. The transition state for thereaction, Z-[OFeO]+ + N2O h Z-[FeO]+(cis-(NO)2), ischaracterized by a decrease in the bond angle of the N2Omolecule from 180 to 152.8° in the transition state, whereasthe length of the N-N′ bond increases from 1.12 to 1.17 Å.The N-O (oxygen bond to the iron atom) bond length is 1.67Å in the transition state. The activation barrier for the nitricoxide dimer isEq ) 28.2 kcal/mol, and the enthalpy of reactionis ∆HR ) 24.4 kcal/mol. The activation barrier for NO formationonZ-[ONOFeO]+,Z-[OFeO2N]+,Z-[OFeO2NO]+,andZ-[OFeOH]+

and the enthalpy of reaction involving these species is slightlysmaller than that for Z-[OFeO]+ (see Table 1 in the Appendix).The imaginary frequency associated with the transition-statemode is 614i cm-1. The activation barrier calculated for thereaction Z-[OFeO]+ + N2O h Z-[FeO]+(cis-(NO)2), 28.2 kcal/mol, is similar to that found by Gonzalez et al.81 for the reactionO(3P) + N2O h 2 NO, 27.7 kcal/mol. The geometry of thetransition-state structure is also quite similar with an O-Ndistance of 1.66 Å, an N-N′ distance of 1.17 Å, and a N2Obending of 157.3° in the transition state. Nitric oxide can desorbfrom Z-[FeO]+(cis-(NO)2) sites. The transition state for thereaction of Z-[FeO]+(cis-(NO)2) to form Z-[FeO]+(ON) andNO is characterized by an increase in the N-N′ bond lengthfrom 1.23 Å in the adsorbed state to 1.44 Å in the transitionstate. The activation barrier for the dissociation isEq ) 9.2 kcal/mol, and the imaginary frequency associated with the transition-state mode is 677i cm-1. The enthalpy of reaction is∆HR )

Figure 9. Catalytic cycle of the N2O dissociation on mononuclearZ-[FeO2N]+{MS ) 5} sites. All energies are zero-point corrected, inkcal/mol and with reference to Z-[FeO2N]+ with the appropriateamounts of N2O, N2, O2, NO, and NO2. Energies of potential-energyminima are in black. Energies of transition states are in red. Energiesof minima on the seam of two PESs are in green. Black structures areon the PES withMS ) 5. Green structures are on the PES withMS )6. Structures in blue are on the PES withMS ) 7. Multiple numbersunder a PES minimum structure correspond to different catalytic cycles(see Table 1).

Figure 10. Alternative catalytic cycle of the N2O dissociation onmononuclear Z-[FeO2N]+{MS ) 5} sites. All energies are zero-pointcorrected, in kcal/mol and with reference to Z-[FeO2N]+ with theappropriate amounts of N2O, N2, O2, NO, and NO2. Energies ofpotential-energy minima are in black. Energies of transition states arein red. Energies of minima on the seam of two PESs are in green.Black structures are on the PES withMS ) 5. Structures in green areon the PES withMS ) 6.


-6.1 kcal/mol. Therefore, at temperatures where N2O decom-position occurs, the dissociation of the NO dimer will be fast.Nitric oxide rapidly desorbs from Z-[FeO]+(ON) sites. The spin-change barrier for desorption isEq ) 4.8 kcal/mol, and theenthalpy of desorption is∆Hdes) 3.3 kcal/mol. Thus, if underreaction conditions a significant fraction of surface sites ispresent intheformofZ-[OFeO]+,Z-[ONOFeO]+,Z-[OFeO2N]+,Z-[OFeO2NO]+, and Z-[OFeOH]+ sites, NO can be formedfrom nitrous oxide. The energetically most demanding step isthe formation of an adsorbed NO dimer; once formed, NOproduction occurs readily.

Since NOx (NO and NO2) rapidly reduces once-oxidized ironsites (e.g., Z-[OFeO]+, Z-[OFeOH]+), NO production is notlikely to occur in the presence of significant amounts of NOx.Therefore, the only scenario in which NO produced from N2O

could significantly influence the rate of N2O decomposition onFe-ZSM-5 would be at low temperatures, where most iron sitesare poisoned by water (i.e., are in the form of Z-[Fe(OH)2]+)and the activity of Fe-ZSM-5 for N2O decomposition is low.

ConclusionsRate coefficients have been determined using a combination

of density functional theory and transition-state theory for anensemble of over 100 elementary reactions that might beinvolved in NO-promoted decomposition of N2O on Fe-ZSM-5at temperatures below 700 K. Under these conditions, highlyactive Z-[FeO]+ sites react with small amounts of water vaporto form Z-[Fe(OH)2]+ sites, which are inactive for N2Odecomposition. NO can react with such species to form HNO2

and Z-[FeOH]+ sites. These newly formed sites are catalyticallyactive for N2O decomposition to N2 and O2. The reactionpathway involves the formation and decomposition of NO2 andis illustrated in Figure 3. Since the activation barrier for theformation of Z-[FeOH]+ sites is low (13.3 kcal/mol), thenumber of active iron sites for the N2O decomposition increasessignificantly in the presence of small amounts of NO, as doesthe N2O decomposition rate. At elevated temperatures, on theother hand, water desorbs from inactive Z-[Fe(OH)2]+ sites,forming active Z-[FeO]+ sites. No net gas species are formedin the process of Z-[FeOH]+ formation, so that at hightemperatures the entropy gain in splitting off an adsorbed watermolecule from Z-[Fe(OH)2]+ centers outweighs the higherenergy barrier for the water desorption reaction.

While iron nitrite and nitrate species were also consideredas possible intermediates in N2O decomposition, these species

Figure 11. Catalytic cycle of the N2O dissociation on mononuclearZ-[FeO2NO]+{MS ) 5} sites. All energies are zero-point corrected, inkcal/mol and with reference to Z-[FeO2NO]+ with the appropriateamounts of N2O, N2, O2, NO, and NO2. Energies of potential-energyminima are in black. Energies of transition states are in red. Energiesof minima on the seam of two PESs are in green. Black structures areon the PES withMS ) 5. Green structures are on the PES withMS )6. Structures in blue are on the PES withMS ) 7. Multiple numbersunder a PES minimum structure correspond to different catalytic cycles(see Table 1).

Figure 12. Alternative catalytic cycle of the N2O dissociation onmononuclear Z-[FeO2NO]+{MS ) 5} sites. All energies are zero-pointcorrected, in kcal/mol and with reference to Z-[FeO2NO]+ with theappropriate amounts of N2O, N2, O2, NO, and NO2. Energies ofpotential-energy minima are in black. Energies of transition states arein red. Energies of minima on the seam of two PESs are in green.Black structures are on the PES withMS ) 5. Structures in green areon the PES withMS ) 6.


were not found to play a significant role in N2O decompositionover Fe-ZSM-5. H2O adsorbs on Z-[FeO]+ species morestrongly than NO, and as a result, small amounts of NO cannotdisplace H2O at low temperatures in order to form iron nitriteor nitrate species. At higher temperatures, both H2O and NOdesorb. In general, iron nitrite and nitrate species are about asactive for N2O decomposition as Z-[FeO]+ and Z-[FeOH]+

species. Consequently, large amounts of NO cannot increasethe overall activity for N2O decomposition by forming ironnitrite and nitrate species.

Finally, the possibility of NO formation from N2O over Fe-ZSM-5 was investigated. Only at low temperatures, where mostiron sites are poisoned by water and the overall catalyst activityfor N2O decomposition is low, it is possible for NO producedfrom N2O to significantly influence the overall activity of Fe-ZSM-5 for N2O decomposition.

Acknowledgment. The authors would like to thank Dr. JensDobler and Dr. Bernd Kallies for support with the TURBO-MOLE V5.6/7 software package. Computations were carried

out at the “Norddeutscher Verbund fu¨r Hoch- und Ho¨chstleis-tungsrechnen” (HLRN)82 on an IBM p690-Cluster. This workwas supported by the Methane Conversion Cooperative fundedby BP, the “Fonds der chemischen Industrie”, and the Max-Buchner-Forschungsstiftung.

AppendixAll rate parameters computed from quantum chemical data

are summarized in Table 1. Calculated enthalpies of reactionare averaged over 600-800 K. To estimate if low spin-inversionprobabilities could result in a significant reduction of the ratesof spin-surface crossing, thermally averaged Landau-Zenertransition probabilities were calculated and are summarized inTable 2 for spin-orbit coupling energies of 395 and 825 J/molfor several temperatures. All spin-inversion transmission coef-ficients are larger than 0.05 (at 700 K). As a result, failure tocorrect reaction rates for spin-inversion probabilities smaller than1 creates errors smaller than an error in the activation barrierof 4 kcal/mol (at 700 K).

Figure 13. Possible pathways for the formation of nitric oxide. All energies are zero-point corrected, in kcal/mol and with reference to Z-[OFeO]+,Z-[OFeONO]+, Z-[OFeO2N]+, Z-[OFeO2NO]+, or Z-[OFeOH]+ with the appropriate amounts of N2O and NO. Energies of potential-energy minimaare in black. Energies of transition states are in red. Energies of minima on the seam of two PESs are in green. Structures in magenta are on thePES withMS ) 4. Black structures are on the PES withMS ) 5. Green structures are on the PES withMS ) 6.


TABLE 1: Computed Rate Parameters for Elementary Steps in NO-Assisted Nitrous Oxide Dissociation over Fe-ZSM-5

T (K)

reactionEq,a ∆Hb

(kcal/mol) constant 600 700 800

1. Z-[FeO]+{M ) 6} + NO(g) T Z-[FeONO]+{M ) 5} ∆H1 ) -32.9 K1, bar-1 1.54× 104 2.87× 102 1.49× 101

E1q ) 1.1 A1, s-1 bar-1 1.43× 105 1.68× 105 1.98× 105

k1, s-1 bar-1 5.93× 104 7.91× 104 1.02× 105

E-1q ) 34.3 A-1, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-1, s-1 3.85× 100 2.76× 102 6.90× 103

2. Z-[FeONO]+{M ) 5} T Z-[Fe]+{M ) 4} + NO2(g) ∆H2 ) 66.0 K2, bar 5.56× 10-18 1.56× 10-14 5.81× 10-12

E2q ) 67.9 A2, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k2, s-1 2.25× 10-12 9.01× 10-9 4.61× 10-6

E-2q ) 0.0 A-2, s-1 bar-1 4.05× 105 5.76× 105 7.93× 105

k-2, s-1 bar-1 4.05× 105 5.76× 105 7.93× 105

3. Z-[FeO]+{M ) 6} + NO(g) T Z-[FeO2N]+{M ) 5} ∆H3 ) -37.8 K3, bar-1 3.07× 105 3.18× 103 1.06× 102

E3q ) 1.4 A3, s-1 bar-1 6.19× 104 7.00× 104 7.98× 104

k3, s-1 bar-1 1.85× 104 2.49× 104 3.23× 104

E-3q ) 39.3 A-3, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-3, s-1 6.04× 10-2 7.81× 100 3.05× 102

4. Z-[FeO2N]+{M ) 5} T Z-[Fe]+{M ) 4} + NO2(g) ∆H4 ) 70.9 K4, bar 2.78× 10-19 1.41× 10-15 8.16× 10-13

E4q ) 72.5 A4, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k4, s-1 4.88× 10-14 3.37× 10-10 2.60× 10-7

E-4q ) 0.0 A-4, s-1 bar-1 1.75× 105 2.39× 105 3.19× 105

k-4, s-1 bar-1 1.75× 105 2.39× 105 3.19× 105

5. Z-[FeO]+{M ) 6} + NO(g) T Z-[OFeNO]+{M ) 5} ∆H5 ) -13.6 K5, bar-1 1.05× 10-2 1.99× 10-3 5.84× 10-4

E5q ) 0.2 A5, s-1 bar-1 5.75× 105 7.38× 105 9.29× 105

k5, s-1 bar-1 4.98× 105 6.51× 105 8.34× 105

E-5q ) 14.9 A-5, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-5, s-1 4.72× 107 3.28× 108 1.43× 109

6. Z-[FeO2]+{M ) 6} + NO(g) T Z-[FeOONO]+{M ) 5} ∆H6 ) -9.0 K6, bar-1 3.90× 10-5 1.28× 10-5 5.71× 10-6

E6q ) 6.3 A6, s-1 bar-1 2.25× 105 2.59× 105 3.00× 105

k6, s-1 bar-1 1.13× 103 2.77× 103 5.65× 103

E-6q ) 15.5 A-6, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-6, s-1 2.89× 107 2.15× 108 9.89× 108

7. Z-[FeOONO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) ∆H7 ) 1.0 K7, bar 1.14× 107 1.32× 107 1.42× 107

E7q ) 2.5 A7, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k7, s-1 1.50× 1012 2.37× 1012 3.40× 1012

E-7q ) 0.0 A-7, s-1 bar-1 1.32× 105 1.80× 105 2.40× 105

k-7, s-1 bar-1 1.32× 105 1.80× 105 2.40× 105

8. Z-[OFeO]+{M ) 6} + NO(g) T Z-[OFeONO]+{M ) 5} ∆H8 ) -30.5 K8, bar-1 6.27× 103 1.57× 102 1.01× 101

E8q ) 3.7 A8, s-1 bar-1 4.05× 105 4.84× 105 5.75× 105

k8, s-1 bar-1 1.86× 104 3.45× 104 5.70× 104

E-8q ) 34.6 A-8, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-8, s-1 2.97× 100 2.20× 102 5.67× 103

9. Z-[OFeONO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) ∆H9 ) 14.4 K9, bar 1.88× 102 1.09× 103 3.89× 103

E9q ) 16.0 A9, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k9, s-1 1.84× 107 1.46× 108 7.04× 108

E-9q ) 0.0 A-9, s-1 bar-1 9.78× 104 1.35× 105 1.81× 105

k-9, s-1 bar-1 9.78× 104 1.35× 105 1.81× 105

10. Z-[OFeO]+{M ) 6} + NO(g) T Z-[OFeO2N]+{M ) 5} ∆H10 ) -34.0 K10, bar-1 3.60× 103 5.96× 101 2.80× 100

E10q ) 4.6 A10, s-1 bar-1 2.61× 104 2.82× 104 3.10× 104

k10, s-1 bar-1 5.48× 102 1.03× 103 1.71× 103

E-10 ) 38.2 A-10, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-10, s-1 1.52× 10-1 1.73× 101 6.11× 102

11. Z-[OFeO2N]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) ∆H11 ) 17.9 K11, bar 3.27× 102 2.85× 103 1.40× 104

E11q ) 19.2 A11, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k11, s-1 1.27× 106 1.48× 107 9.51× 107

E-11q ) 0.6 A-11, s-1 bar-1 6.31× 103 7.86× 103 9.77× 103

k-11, s-1 bar-1 3.89× 103 5.19× 103 6.80× 103

12. Z-[OFeO]+{M ) 6} + NO(g) T Z-[FeO2NO]+{M ) 5} ∆H12 ) -58.3 K12, bar-1 1.89× 1012 1.70× 109 8.95× 106

E12q ) 5.8 A12, s-1 bar-1 2.87× 104 2.93× 104 3.07× 104

k12, s-1 bar-1 2.18× 102 4.47× 102 7.90× 102

E-12q ) 63.2 A-12, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-12, s-1 1.15× 10-10 2.63× 10-7 8.83× 10-5

13. Z-[FeO2NO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) ∆H13 ) 42.2 K13, bar 6.23× 10-7 9.99× 10-5 4.37× 10-3

E13q ) 44.2 A13, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k13, s-1 9.67× 10-4 2.26× 10-1 1.37× 101

E-13q ) 1.8 A-13, s-1 bar-1 6.94× 103 8.16× 103 9.66× 103

k-13, s-1 bar-1 1.55× 103 2.26× 103 3.14× 103

14. Z-[FeONO]+{M ) 5} + N2O(g) T Z-[FeONO]+(N2O){M ) 5} ∆H14 ) -3.1 K14, bar-1 4.87× 10-5 3.28× 10-5 2.50× 10-5

E14q ) 0.0 A14, s-1 bar-1 1.17× 107 1.61× 107 2.15× 107

k14, s-1 bar-1 1.17× 107 1.61× 107 2.15× 107

E-14q ) 4.7 A-14, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-14, s-1 2.39× 1011 4.91× 1011 8.58× 1011


TABLE 1: (Continued)

T (K)

reactionEq,a ∆Hb


15. Z-[FeONO]+{M ) 5} + N2O(g) T Z-[FeONO]+(ON2){M ) 5} ∆H15 ) -1.5 K15, bar-1 5.00× 10-5 4.09× 10-5 3.61× 10-5

E15q ) 0.0 A15, s-1 bar-1 3.99× 107 5.64× 107 7.65× 107

k15, s-1 bar-1 3.99× 107 5.64× 107 7.65× 107

E-15q ) 3.3 A-15, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-15, s-1 7.98× 1011 1.38× 1012 2.12× 1012

16. Z-[FeONO]+(ON2){M ) 5} T Z-[OFeONO]+{M ) 5} + N2(g) ∆H16 ) -12.7 K16, bar 5.21× 109 1.16× 109 3.66× 108

E16q ) 24.8 A16, s-1 3.39× 1013 3.97× 1013 4.52× 1013

k16, s-1 3.08× 104 7.07× 105 7.49× 106

E-16q ) 36.8 A-16, s-1 bar-1 1.58× 108 1.97× 108 2.40× 108

k-16, s-1 bar-1 5.91× 10-6 6.11× 10-4 2.05× 10-2

17. Z-[OFeONO]+{M ) 5} + N2O(g) T Z-[OFeONO]+(N2O){M ) 5} ∆H17 ) -0.5 K17, bar-1 1.84× 10-6 1.71× 10-6 1.66× 10-6

E17q ) 0.0 A17, s-1 bar-1 5.24× 106 7.03× 106 9.15× 106

k17, s-1 bar-1 5.24× 106 7.03× 106 9.15× 106

E-17q ) 1.8 A-17, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-17, s-1 2.85× 1012 4.10× 1012 5.50× 1012

18. Z-[OFeONO]+{M ) 5} + N2O(g) T Z-[OFeONO]+(ON2){M ) 5} ∆H18 ) -1.5 K18, bar-1 1.41× 10-6 1.16× 10-6 1.03× 10-6

E18q ) 0.0 A18, s-1 bar-1 1.72× 106 2.30× 106 3.00× 106

k18, s-1 bar-1 1.72× 106 2.30× 106 3.00× 106

E-18q ) 2.8 A-18, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-18, s-1 1.22× 1012 1.98× 1012 2.91× 1012

19. Z-[OFeONO]+(ON2){M ) 5} T Z-[O2FeONO]+{M ) 5} + N2(g) ∆H19 ) -20.7 K19, bar 2.79× 1015 2.35× 1014 3.60× 1013

E19q )44.9 A19, s-1 1.80× 1014 2.16× 1014 2.51× 1014

k19, s-1 7.76× 10-3 2.03× 100 1.33× 102

E-19q ) 66.2 A-19, s-1 bar-1 3.64× 106 4.05× 106 4.53× 106

k-19, s-1 bar-1 2.79× 10-18 8.64× 10-15 3.70× 10-12

20. Z-[O2FeONO]+{M ) 5} T Z-[O2FeONO]+{M ) 7} ∆H20 ) -5.4 K20, - 4.83× 101 2.52× 101 1.54× 101

E20q ) 7.1 A20, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k20, s-1 3.31× 1010 9.02× 1010 1.95× 1011

E-20q ) 12.4 A-20, s-1 2.22× 1013 2.64× 1013 3.05× 1013

k-20, s-1 6.85× 108 3.58× 109 1.26× 1010

21. Z-[O2FeONO]+{M ) 7} T Z-[FeONO]+{M ) 5} + O2(g) ∆H21 ) 3.3 K21, bar 1.35× 105 2.05× 105 2.72× 105

E21q ) 6.0 A21, s-1 1.11× 1014 1.22× 1014 1.30× 1014

k21, s-1 7.12× 1011 1.60× 1012 2.94× 1012

E-21q ) 1.5 A-21, s-1 bar-1 1.92× 107 2.37× 107 2.85× 107

k-21, s-1 bar-1 5.28× 106 7.82× 106 1.08× 107

22. Z-[O2FeONO]+{M ) 7} T Z-[FeO2]+{M ) 6} + NO2(g) ∆H22 ) 17.3 K22, bar 1.68× 100 1.37× 101 6.40× 101

E22q ) 19.4 A22, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k22, s-1 1.07× 106 1.28× 107 8.34× 107

E-22q ) 0.0 A-22, s-1 bar-1 6.38× 105 9.29× 105 1.30× 106

k-22, s-1 bar-1 6.38× 105 9.29× 105 1.30× 106

23. Z-[OFeONO]+{M ) 5} + NO(g) T Z-[Fe(ONO)2]+{M ) 6} ∆H23 ) -31.7 K23, bar-1 1.31× 106 2.83× 104 1.64× 103

E23q ) 0.0 A23, s-1 bar-1 1.73× 107 2.24× 107 2.84× 107

k23, s-1 bar-1 1.73× 107 2.24× 107 2.84× 107

E-23q ) 32.9 A-23, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-23, s-1 1.32× 101 7.90× 102 1.73× 104

24. Z-[Fe(ONO)2]+{M ) 6} T Z-[FeONO]+{M ) 5} + NO2(g) ∆H24 ) 13.2 K24, bar 2.20× 100 1.10× 101 3.53× 101

E24q ) 15.6 A24, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k24, s-1 2.60× 107 1.97× 108 9.13× 108

E-24q ) 0.0 A-24, s-1 bar-1 1.18× 107 1.79× 107 2.59× 107

k-24, s-1 bar-1 1.18× 107 1.79× 107 2.59× 107

25. Z-[Fe(ONO)2]+{M ) 6} T Z-[ONOFeO2N]+{M ) 6} ∆H25 ) -4.7 K25, - 1.39× 100 7.98× 10-1 5.24× 10-1

E25q ) 1.3 A25, s-1 8.12× 1011 8.05× 1011 7.99× 1011

k25, s-1 2.80× 1011 3.23× 1011 3.60× 1011

E-25q ) 5.3 A-25, s-1 1.65× 1013 1.77× 1013 1.87× 1013

k-25, s-1 2.01× 1011 4.05× 1011 6.87× 1011

26. Z-[OFeONO]+{M ) 5} T Z-[FeO2NO]+{M ) 5} ∆H26 ) -27.8 K26, - 3.02× 108 1.09× 107 8.89× 105

E26q ) 10.0 A26, s-1 3.51× 1012 3.69× 1012 3.83× 1012

k26, s-1 7.69× 108 2.69× 109 6.90× 109E-26

q ) 36.5 A-26, s-1 4.95× 1013 6.08× 1013 7.19× 1013

k-26, s-1 2.55× 100 2.48× 102 7.76× 10327. Z-[FeONO]+{M ) 5} T Z-[FeO2N]+{M ) 5} ∆H27 ) -4.9 K27, - 2.00× 101 1.11× 101 7.12× 100

E27q ) 3.0 A27, s-1 2.84× 1013 2.97× 1013 3.07× 1013

k27, s-1 2.36× 1012 3.52× 1012 4.75× 1012

E-27q ) 7.5 A-27, s-1 6.57× 1013 7.14× 1013 7.62× 1013

k-27, s-1 1.18× 1011 3.18× 1011 6.67× 1011

28. Z-[FeO2N]+{M ) 5} + N2O(g) T Z-[FeO2N]+(N2O){M ) 5} ∆H28 ) -4.2 K28, bar-1 3.19× 10-5 1.89× 10-5 1.31× 10-5

E28q ) 0.0 A28, s-1 bar-1 3.41× 106 4.66× 106 6.15× 106

k28, s-1 bar-1 3.41× 106 4.66× 106 6.15× 106

E-28q ) 5.7 A-28, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-28, s-1 1.07× 1011 2.47× 1011 4.69× 1011



T (K)

reactionEq,a ∆Hb


29. Z-[FeO2N]+{M ) 5} + N2O(g) T Z-[FeO2N]+(ON2){M ) 5} ∆H29 ) -2.5 K29, bar-1 4.22× 10-5 3.06× 10-5 2.47× 10-5

E29q ) 0.0 A29, s-1 bar-1 1.60× 107 2.23× 107 2.99× 107

k29, s-1 bar-1 1.60× 107 2.23× 107 2.99× 107

E-29q ) 4.2 A-29, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-29, s-1 3.79× 1011 7.28× 1011 1.21× 1012

30. Z-[FeO2N]+(ON2){M ) 5} T Z-[OFeO2N]+{M ) 5} + N2(g) ∆H30 ) -10.2 K30, bar 1.78× 108 5.30× 107 2.09× 107

E30q ) 25.4 A30, s-1 1.42× 1013 1.63× 1013 1.83× 1013

k30, s-1 7.73× 103 1.87× 105 2.07× 106

E-30q ) 34.6 A-30, s-1 bar-1 1.77× 108 2.27× 108 2.83× 108

k-30, s-1 bar-1 4.35× 10-5 3.54× 10-3 9.88× 10-2

31. Z-[OFeO2N]+{M ) 5} + N2O(g) T Z-[OFeO2N]+(N2O){M ) 5} ∆H31 ) 1.6 K31, bar-1 1.74× 10-4 2.07× 10-4 2.42× 10-4

E31q ) 0.0 A31, s-1 bar-1 1.64× 109 2.37× 109 3.27× 109

k31, s-1 bar-1 1.64× 109 2.37× 109 3.27× 109

E-31q ) 0.3 A-31, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-31, s-1 9.45× 1012 1.15× 1013 1.35× 1013

32. Z-[OFeO2N]+{M ) 5} + N2O(g) T Z-[OFeO2N]+(ON2){M ) 5} ∆H32 ) -2.7 K32, bar-1 1.45× 10-5 1.03× 10-5 8.17× 10-6

E32q ) 0.0 A32, s-1 bar-1 4.90× 106 6.79× 106 9.08× 106

k32, s-1 bar-1 4.90× 106 6.79× 106 9.08× 106

E-32q ) 4.3 A-32, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-32, s-1 3.38× 1011 6.60× 1011 1.11× 1012

33. Z-[OFeO2N]+ (ON2){M ) 5} T Z-[O2FeO2N]+{M ) 5} + N2(g) ∆H33 ) -16.1 K33, bar 3.81× 1013 5.61× 1012 1.31× 1012

E33q ) 45.2 A33, s-1 1.59× 1014 1.89× 1014 2.18× 1014

k33, s-1 5.15× 10-3 1.39× 100 9.36× 101

E-33q ) 61.8 A-33, s-1 bar-1 4.58× 106 5.07× 106 5.65× 106

k-33, s-1 bar-1 1.35× 10-16 2.48× 10-13 7.15× 10-11

34. Z-[O2FeO2N]+{M ) 5} T Z-[O2FeO2N]+{M ) 7} ∆H34 ) -7.7 K34, - 5.97× 102 2.37× 102 1.19× 102

E34q ) 0.1 A34, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k34, s-1 1.11× 1013 1.32× 1013 1.52× 1013

E-34q ) 7.8 A-34, s-1 1.31× 1013 1.53× 1013 1.76× 1013

k-34, s-1 1.86× 1010 5.55× 1010 1.28× 1011

35. Z-[O2FeO2N]+{M ) 7} T Z-[FeO2N]+{M ) 5} + O2(g) ∆H35 ) 0.7 K35, bar-1 2.70× 106 2.99× 106 3.14× 106

E35q ) 3.0 A35, s-1 bar-1 1.30× 1013 1.38× 1013 1.44× 1013

k35, s-1 bar-1 1.08× 1012 1.64× 1012 2.23× 1012

E-35q ) 1.2 A-35, s-1 1.13× 106 1.33× 106 1.55× 106

k-35, s-1 4.01× 105 5.47× 105 7.11× 105

36. Z-[O2FeO2N]+{M ) 7} T Z-[FeO2]+{M ) 6} + NO2(g) ∆H36 ) 19.6 K36, bar 1.68× 100 1.81× 101 1.04× 102

E36q ) 21.2 A36, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k36, s-1 2.34× 105 3.47× 106 2.67× 107

E-36q ) 0.0 A-36, s-1 bar-1 1.39× 105 1.92× 105 2.57× 105

k-36, s-1 bar-1 1.39× 105 1.92× 105 2.57× 105

37. Z-[OFeO2N]+{M ) 5} + NO(g) T Z-[ONOFeO2N]+{M ) 6} ∆H37 ) -32.9 K37, bar-1 3.19× 106 5.94× 104 3.08× 103

E37q ) 0.0 A37, s-1 bar-1 1.32× 107 1.74× 107 2.24× 107

k37, s-1 bar-1 1.32× 107 1.74× 107 2.24× 107

E-37q ) 34.2 A-37, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-37, s-1 4.14× 100 2.93× 102 7.28× 103

38. Z-[ONOFeO2N]+{M ) 6} T Z-[FeO2N]+{M ) 5} + NO2(g) ∆H38 ) 12.9 K38, bar 3.15× 101 1.53× 102 4.80× 102

E38q ) 15.0 A38, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k38, s-1 4.24× 107 2.99× 108 1.32× 109

E-38q ) 0.0 A-38, s-1 bar-1 1.35× 106 1.96× 106 2.75× 106

k-38, s-1 bar-1 1.35× 106 1.96× 106 2.75× 106

39. Z-[ONOFeO2N]+{M ) 6} T Z-[Fe(O2N)2]+{M ) 6} ∆H39 ) -0.6 K39, - 4.14× 10-2 3.87× 10-2 3.67× 10-2

E39q ) 2.8 A39, s-1 3.65× 1011 3.56× 1011 3.50× 1011

k39, s-1 3.46× 1010 4.72× 1010 5.97× 1010

E-39q ) 2.7 A-39, s-1 8.13× 1012 8.58× 1012 8.96× 1012

k-39, s-1 8.35× 1011 1.22× 1012 1.63× 1012

40. Z-[OFeO2N]+{M ) 5} T Z-[OFeONO]+{M ) 5} ∆H40 ) 3.5 K40, - 1.74× 100 2.63× 100 3.59× 100

E40q ) 5.6 A40, s-1 3.73× 1013 4.20× 1013 4.61× 1013

k40, s-1 3.50× 1011 7.68× 1011 1.39× 1012

E-40q ) 3.0 A-40, s-1 2.41× 1012 2.45× 1012 2.49× 1012

k-40, s-1 2.01× 1011 2.92× 1011 3.86× 1011

41. Z-[FeO2N]+{M ) 5} + N2O(g) T Z-[FeO2NO]+{M ) 5} + N2(g) ∆H41 ) -37.1 K41, - 3.94× 1012 4.63× 1010 1.65× 109

E41q ) 49.6 A41, s-1 2.53× 108 3.44× 108 4.50× 108

k41, s-1 2.11× 10-10 1.10× 10-7 1.24× 10-5

E-41q ) 86.8 A-41, s-1 2.25× 109 3.03× 109 3.92× 109

k-41, s-1 5.35× 10-23 2.37× 10-18 7.51× 10-15

42. Z-[FeO2NO]+{M ) 5} + N2O(g) T Z-[FeO2NO]+(N2O){M ) 5} ∆H42 ) -1.8 K42, bar-1 2.61× 10-5 2.05× 10-5 1.76× 10-5

E42q ) 0.0 A42, s-1 bar-1 1.82× 107 2.52× 107 3.37× 107

k42, s-1 bar-1 1.82× 107 2.52× 107 3.37× 107

E-42q ) 3.4 A-42, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-42, s-1 6.97× 1011 1.23× 1012 1.91× 1012



T (K)

reactionEq,a ∆Hb


43. Z-[FeO2NO]+{M ) 5} + N2O(g) T Z-[FeO2NO]+(ON2){M ) 5} ∆H43 ) -1.0 K43, bar-1 9.10× 10-6 7.89× 10-6 7.28× 10-6

E43q ) 0.0 A43, s-1 bar-1 1.14× 107 1.61× 107 2.17× 107

k43, s-1 bar-1 1.14× 107 1.61× 107 2.17× 107

E-43q ) 2.7 A-43, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-43, s-1 1.26× 1012 2.03× 1012 2.97× 1012

44. Z-[FeO2NO]+(ON2){M ) 5} T Z-[OFeO2NO]+{M ) 5} + N2(g) ∆H44 ) -7.0 K44, bar 2.50× 107 1.10× 107 5.79× 106

E44q ) 25.2 A44, s-1 3.42× 1013 3.99× 1013 4.52× 1013

k44, s-1 2.27× 104 5.41× 105 5.91× 106

E-44q ) 31.2 A-44, s-1 bar-1 2.13× 108 2.75× 108 3.43× 108

k-44, s-1 bar-1 9.07× 10-4 4.93× 10-2 1.02× 100

45. Z-[OFeO2NO]+{M ) 5} + N2O(g) T Z-[OFeO2NO]+(N2O){M ) 5} ∆H45 ) -2.6 K45, bar-1 8.56× 10-6 6.17× 10-6 4.95× 10-6

E45q ) 0.0 A45, s-1 bar-1 3.45× 106 4.73× 106 6.27× 106

k45, s-1 bar-1 3.45× 106 4.73× 106 6.27× 106

E-45q ) 4.1 A-45, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-45, s-1 4.03× 1011 7.67× 1011 1.27× 1012

46. Z-[OFeO2NO]+{M ) 5} + N2O(g) T Z-[OFeO2NO]+(ON2){M ) 5} ∆H46 ) -2.9 K46, bar-1 3.87× 10-6 2.67× 10-6 2.07× 10-6

E46q ) 0.0 A46, s-1 bar-1 1.14× 106 1.57× 106 2.08× 106

k46, s-1 bar-1 1.14× 106 1.57× 106 2.08× 106

E-46q ) 4.5 A-46, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-46, s-1 2.95× 1011 5.89× 1011 1.00× 1012

47. Z-[OFeO2NO]+(ON2){M ) 5} T Z-[O2FeO2NO]+{M ) 5} + N2(g) ∆H47 ) -19.2 K47, bar 6.52× 1015 6.60× 1014 1.16× 1014

E47q ) 41.1 A47, s-1 1.02× 1013 1.18× 1013 1.32× 1013

k47, s-1 1.05× 10-2 1.67× 100 7.60× 101

E-47q ) 61.0 A-47, s-1 bar-1 2.67× 104 2.82× 104 3.02× 104

k-47, s-1 bar-1 1.61× 10-18 2.54× 10-15 6.53× 10-13

48. Z-[O2FeO2NO]+{M ) 5} T Z-[O2FeO2NO]+{M ) 7} ∆H48 ) -8.7 K48, - 6.26× 102 2.20× 102 1.01× 102

E48q ) 0.4 A48, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k48, s-1 9.24× 1012 1.13× 1013 1.33× 1013

E-48q ) 8.9 A-48, s-1 2.63× 1013 3.12× 1013 3.62× 1013

k-48, s-1 1.48× 1010 5.11× 1010 1.32× 1011

49. Z-[O2FeO2NO]+{M ) 7} T Z-[FeO2NO]+{M ) 5} + O2(g) ∆H49 ) 0.4 K49, bar 1.86× 106 1.98× 106 2.01× 106

E49q ) 3.0 A49, s-1 1.91× 1013 2.04× 1013 2.15× 1013

k49, s-1 1.57× 1012 2.40× 1012 3.30× 1012

E-49q ) 1.5 A-49, s-1 bar-1 3.07× 106 3.68× 106 4.32× 106

k-49, s-1 bar-1 8.45× 105 1.21× 106 1.64× 106

50. Z-[O2FeO2NO]+{M ) 7} T Z-[OFeO2]+{M ) 6} + NO2(g) ∆H50 ) 43.2 K50, bar 3.88× 10-9 8.05× 10-7 4.34× 10-5

E50q ) 44.0 A50, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k50, s-1 1.16× 10-3 2.65× 10-1 1.58× 101

E-50q ) 0.0 A-50, s-1 bar-1 3.00× 105 3.29× 105 3.64× 105

k-50, s-1 bar-1 3.00× 105 3.29× 105 3.64× 105

51. Z-[OFeO2NO]+{M ) 5} T Z-[OFeO]+{M ) 6} + NO2(g) ∆H51 ) 33.6 K51, bar 1.75× 10-3 1.00× 10-1 2.02× 100

E51q ) 40.8 A51, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k51, s-1 1.71× 10-2 2.65× 100 1.18× 102

E-51q ) 7.2 A-51, s-1 bar-1 4.22× 103 4.81× 103 5.55× 103

k-51, s-1 bar-1 9.76× 100 2.65× 101 5.86× 101

52. Z-[OFeO2NO]+{M ) 5} + NO(g) T Z-[ONOFeO2NO]+{M ) 6} ∆H52 ) -37.0 K52, bar-1 8.49× 107 9.67× 105 3.46× 104

E52q ) 0.0 A52, s-1 bar-1 1.18× 107 1.55× 107 1.98× 107

k52, s-1 bar-1 1.18× 107 1.55× 107 1.98× 107

E-52q ) 38.3 A-52, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-52, s-1 1.39× 10-1 1.60× 101 5.71× 102

53. Z-[ONOFeO2NO]+{M ) 6} T Z-[FeO2NO]+{M ) 5} + NO2(g) ∆H53 ) 12.3 K53, bar 3.90× 101 1.76× 102 5.23× 102

E53q ) 14.5 A53, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k53, s-1 6.76× 107 4.46× 108 1.87× 109

E-53q ) 0.0 A-53, s-1 bar-1 1.73× 106 2.54× 106 3.57× 106

k-53, s-1 bar-1 1.73× 106 2.54× 106 3.57× 106

54. Z-[ONOFeO2NO]+{M ) 6} T Z-[NO2FeO2NO]+{M ) 6} ∆H54 ) -1.3 K54, - 5.53× 10-2 4.75× 10-2 4.22× 10-2

E54q ) 2.5 A54, s-1 5.32× 1011 5.20× 1011 5.10× 1011

k54, s-1 6.70× 1010 8.80× 1010 1.08× 1011

E-54q ) 3.0 A-54, s-1 1.52× 1013 1.61× 1013 1.70× 1013

k-54, s-1 1.21× 1012 1.85× 1012 2.55× 1012

55. Z-[Fe(OH)2]+{M ) 6} + NO(g) T Z-[Fe(OH)2]+(ON){M ) 7} ∆H55 ) 1.1 K55, bar-1 3.00× 10-5 3.29× 10-5 3.62× 10-5

E55q ) 0.0 A55, s-1 bar-1 2.46× 108 3.34× 108 4.39× 108

k55, s-1 bar-1 2.46× 108 3.34× 108 4.39× 108

E-55q ) 0.5 A-55, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-55, s-1 8.18× 1012 1.01× 1013 1.21× 1013

56. Z-[Fe(OH)2]+{M ) 6} + NO(g) T Z-[Fe(OH)2]+(NO){M ) 7} ∆H56 ) -0.9 K56, bar-1 2.37× 10-5 2.05× 10-5 1.89× 10-5

E56q ) 0.0 A56, s-1 bar-1 5.01× 107 6.52× 107 8.28× 107

k56, s-1 bar-1 5.01× 107 6.52× 107 8.28× 107

E-56q ) 2.1 A-56, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-56, s-1 2.11× 1012 3.17× 1012 4.39× 1012



T (K)

reactionEq,a ∆Hb


57. Z-[Fe(OH)2]+(NO){M ) 7} T Z-[Fe(OH)2]+(NO){M ) 5} ∆H57 ) -0.01 K57, - 5.20× 10-1 5.20× 10-1 5.19× 10-1

E57q ) 0.1 A57, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k57, s-1 1.19× 1013 1.40× 1013 1.61× 1013

E-57q ) 0.03 A-57, s-1 2.35× 1013 2.76× 1013 3.16× 1013

k-57, s-1 2.30× 1013 2.70× 1013 3.10× 1013

58. Z-[Fe(OH)2]+(NO){M ) 5} T Z-[FeOH]+(trans-HNO2){M ) 5} ∆H58 ) 6.4 K58, - 2.16× 10-5 4.68× 10-5 8.29× 10-5

E58q ) 9.7 A58, s-1 3.72× 1012 3.75× 1012 3.77× 1012

k58, s-1 1.05× 109 3.40× 109 8.20× 109

E-58q ) 2.3 A-58, s-1 3.22× 1014 3.68× 1014 4.09× 1014

k-58, s-1 4.84× 1013 7.26× 1013 9.89× 1013

59. Z-[Fe(OH)2]+(NO){M ) 5} T Z-[FeOH]+(cis-HNO2){M ) 5} ∆H59 ) 8.7 K59, - 7.12× 10-6 2.04× 10-5 4.45× 10-5

E59q ) 11.0 A59, s-1 1.13× 1011 1.06× 1011 1.00× 1011

k59, s-1 1.09× 107 3.82× 107 9.76× 107

E-59q ) 1.3 A-59, s-1 4.49× 1012 4.72× 1012 4.91× 1012

k-59, s-1 1.53× 1012 1.88× 1012 2.19× 1012

60. Z-[FeOH]+(trans-HNO2){M ) 5} T Z-[FeOH]+{M ) 5} + ∆H60 ) 5.9 K60, bar 4.84× 104 1.01× 105 1.68× 105

trans-HNO2(g) E60q ) 7.9 A60, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k60, s-1 1.61× 1010 4.87× 1010 1.14× 1011

E-60q ) 0.0 A-60, s-1 bar-1 3.33× 105 4.84× 105 6.76× 105

k-60, s-1 bar-1 3.33× 105 4.84× 105 6.76× 105

61. Z-[FeOH]+(cis-HNO2){M ) 5} T Z-[FeOH]+{M ) 5} + ∆H61 ) 4.3 K61, bar 6.45× 104 1.11× 105 1.61× 105

cis-HNO2(g) E61q ) 6.6 A61, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k61, s-1 5.06× 1010 1.30× 1011 2.68× 1011

E-61q ) 0.0 A-61, s-1 bar-1 7.85× 105 1.17× 106 1.66× 106

k-61, s-1 bar-1 7.85× 105 1.17× 106 1.66× 106

62. Z-[FeOH]+{M ) 5} + N2O(g) T Z-[FeOH]+(N2O){M ) 5} ∆H62 ) -1.4 K62, bar-1 1.40× 10-4 1.17× 10-4 1.05× 10-4

E62q ) 0.0 A62, s-1 bar-1 1.21× 108 1.73× 108 2.35× 108

k62, s-1 bar-1 1.21× 108 1.73× 108 2.35× 108

E-62q ) 3.2 A-62, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-62, s-1 8.65× 1011 1.48× 1012 2.25× 1012

63. Z-[FeOH]+{M ) 5} + N2O(g) T Z-[FeOH]+(ON2){M ) 5} ∆H63 ) -1.8 K63, bar-1 3.61× 10-5 2.85× 10-5 2.45× 10-5

E63q ) 0.0 A63, s-1 bar-1 2.45× 107 3.42× 107 4.60× 107

k63, s-1 bar-1 2.45× 107 3.42× 107 4.60× 107

E-63q ) 3.5 A-63, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-63, s-1 6.79× 1011 1.20× 1012 1.87× 1012

64. Z-[FeOH]+(ON2){M ) 5} T Z-[OFeOH]+{M ) 5} + N2(g) ∆H64 ) -16.1 K64, bar 2.31× 1010 3.42× 109 7.95× 108

E64q ) 24.0 A64, s-1 8.07× 1011 8.76× 1011 9.40× 1011

k64, s-1 1.49× 103 2.85× 104 2.64× 105

E-64q ) 38.8 A-64, s-1 bar-1 8.52× 106 1.06× 107 1.30× 107

k-64, s-1 bar-1 6.43× 10-8 8.35× 10-6 3.32× 10-4

65. Z-[OFeOH]+{M ) 5} + N2O(g) T Z-[OFeOH]+(N2O){M ) 5} ∆H65 ) -0.8 K65, bar-1 1.25× 10-4 1.11× 10-4 1.04× 10-4

E65q ) 0.0 A65, s-1 bar-1 1.92× 108 2.68× 108 3.60× 108

k65, s-1 bar-1 1.92× 108 2.68× 108 3.60× 108

E-65q ) 2.5 A-65, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-65, s-1 1.54× 1012 2.42× 1012 3.46× 1012

66. Z-[OFeOH]+{M ) 5} + N2O(g) T Z-[OFeOH]+(ON2){M ) 5} ∆H66 ) -1.5 K66, bar-1 5.86× 10-5 4.83× 10-5 4.29× 10-5

E66q ) 0.0 A66, s-1 bar-1 5.59× 107 7.76× 107 1.04× 108

k66, s-1 bar-1 5.59× 107 7.76× 107 1.04× 108

E-66q ) 3.1 A-66, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-66, s-1 9.54× 1011 1.61× 1012 2.42× 1012

67. Z-[OFeOH]+(ON2){M ) 5} T Z-[O2FeOH]+{M ) 5} + N2(g) ∆H67 ) -20.5 K67, bar 6.27× 1013 5.42× 1012 8.53× 1011

E67q ) 46.5 A67, s-1 5.48× 1012 6.52× 1012 7.54× 1012

k67, s-1 6.10× 10-5 1.92× 10-2 1.45× 100

E-67q ) 67.7 A-67, s-1 bar-1 4.70× 106 5.09× 106 5.56× 106

k-67, s-1 bar-1 9.73× 10-19 3.54× 10-15 1.71× 10-12

68. Z-[O2FeOH]+{M ) 5} T Z-[O2FeOH]+{M ) 7} ∆H68 ) -4.5 K68, - 6.09× 101 3.57× 101 2.39× 101

E68q ) 6.0 A68, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k68, s-1 8.19× 1010 1.96× 1011 3.84× 1011

E-68q ) 10.5 A-68, s-1 8.75× 1012 1.02× 1013 1.16× 1013

k-68, s-1 1.34× 109 5.49× 109 1.61× 1010

69. Z-[O2FeOH]+{M ) 7} T Z-[FeOH]+{M ) 5} + O2(g) ∆H69 ) 5.8 K69, bar 3.58× 104 7.30× 104 1.21× 105

E69q ) 7.6 A69, s-1 7.23× 1013 7.93× 1013 8.50× 1013

k69, s-1 1.22× 1011 3.32× 1011 7.05× 1011

E-69q ) 0.8 A-69, s-1 bar-1 6.59× 106 8.03× 106 9.58× 106

k-69, s-1 bar-1 3.40× 106 4.55× 106 5.82× 106

70. Z-[OFeOH]+{M ) 5} + NO(g) T Z-[ONOFeOH]+{M ) 6} ∆H70 ) -31.6 K70, bar-1 2.09× 105 4.56× 103 2.66× 102

E70q ) 0.0 A70, s-1 bar-1 2.60× 106 3.42× 106 4.42× 106

k70, s-1 bar-1 2.60× 106 3.42× 106 4.42× 106

E-70q ) 32.9 A-70, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-70, s-1 1.24× 101 7.51× 102 1.66× 104



T (K)

reactionEq,a ∆Hb


71. Z-[ONOFeOH]+{M ) 6} T Z-[FeOH]+{M ) 5} + NO2(g) ∆H71 ) 16.8 K71, bar 4.32× 100 3.32× 101 1.47× 102

E71q ) 18.6 A71, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k71, s-1 2.08× 106 2.25× 107 1.37× 108

E-71q ) 0.0 A-71, s-1 bar-1 4.81× 105 6.80× 105 9.32× 105

k-71, s-1 bar-1 4.81× 105 6.80× 105 9.32× 105

72. Z-[OFeOH]+{M ) 5} + NO(g) T Z-[FeO]+(trans-HNO2){M ) 6} ∆H72 ) -0.2 K72, bar-1 1.14× 10-6 1.07× 10-6 1.05× 10-6

E72q ) 0.0 A72, s-1 bar-1 4.28× 106 5.56× 106 7.07× 106

k72, s-1 bar-1 4.28× 106 5.56× 106 7.07× 106

E-72q ) 1.4 A-72, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-72, s-1 3.74× 1012 5.19× 1012 6.75× 1012

73. Z-[FeO]+(trans-HNO2){M ) 6} T Z-[FeO]+{M ) 6} + ∆H73 ) 11.2 K73, bar 3.08× 102 1.21× 103 3.25× 103

trans-HNO2(g) E73q ) 13.5 A73, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k73, s-1 1.55× 108 9.06× 108 3.47× 109

E-73q ) 0.0 A-73, s-1 bar-1 5.01× 105 7.48× 105 1.07× 106

k-73, s-1 bar-1 5.01× 105 7.48× 105 1.07× 106

74. Z-[OFeOH]+{M ) 5} + trans-HNO2(g) T ∆H74 ) -8.8 K74, bar-1 7.84× 10-6 2.68× 10-6 1.23× 10-6

Z-[OFeOH]+(trans-HNO2){M ) 5} E74q ) 0.0 A74, s-1 bar-1 3.33× 104 4.16× 104 5.15× 104

k74, s-1 bar-1 3.33× 104 4.16× 104 5.15× 104

E-74q ) 9.5 A-74, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k-74, s-1 4.25× 109 1.55× 1010 4.18× 1010

75. Z-[OFeOH]+(trans-HNO2){M ) 5} T Z-[OFeOH2]+(NO2){M ) 5} ∆H75 ) -1.4 K75, - 7.07× 100 5.99× 100 5.30× 100

E75q ) 1.9 A75, s-1 2.06× 1012 2.14× 1012 2.22× 1012

k75, s-1 4.02× 1011 5.27× 1011 6.51× 1011

E-75q ) 3.9 A-75, s-1 1.52× 1012 1.47× 1012 1.44× 1012

k-75, s-1 5.68× 1010 8.81× 1010 1.23× 1011

76. Z-[OFeOH2]+(NO2){M ) 5} T Z-[OFeOH2]+(NO2){M ) 7} ∆H76 ) 7.3 K76, - 6.63× 100 1.59× 101 3.06× 101

E76q ) 6.8 A76, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k76, s-1 4.22× 1010 1.11× 1011 2.33× 1011

E-76q ) 0.8 A-76, s-1 1.29× 1010 1.28× 1010 1.30× 1010

k-76, s-1 6.37× 109 7.00× 109 7.63× 109

77. Z-[OFeOH2]+(NO2){M ) 7} T Z-[FeO]+(OH2){M ) 6} + NO2(g) ∆H77 ) 3.7 K77, bar 1.04× 105 1.66× 105 2.30× 105

E77q ) 5.2 A77, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k77, s-1 1.64× 1011 3.56× 1011 6.47× 1011

E-77q ) 0.0 A-77, s-1 bar-1 1.58× 106 2.14× 106 2.82× 106

k-77, s-1 bar-1 1.58× 106 2.14× 106 2.82× 106

78. Z- [FeO]+(OH2){M ) 6} T Z-[FeO]+{M ) 6} + H2O(g)c ∆H78 ) 16.3 K78, bar 1.01× 100 7.35× 100 3.14× 101

E78q ) 17.3 A78, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k78, s-1 6.13× 106 5.70× 107 3.09× 108

E-78q ) 0.0 A-78, s-1 bar-1 6.04× 106 7.75× 106 9.82× 106

k-78, s-1 bar-1 6.04× 106 7.75× 106 9.82× 106

79. Z- [FeO]+(OH2){M ) 6} T Z-[Fe(OH)2]+{M ) 6} ∆H79 ) -27.1 K79, - 1.83× 109 7.10× 107 6.26× 106

E79q ) 9.2 A79, s-1 2.28× 1012 2.18× 1012 2.13× 1012

k79, s-1 1.03× 109 2.97× 109 6.60× 109

E-79q ) 36.4 A-79, s-1 1.08× 1013 1.02× 1013 9.69× 1012

k-79, s-1 5.63× 10-1 4.18× 101 1.05× 103

80. Z-[OFeO]+{M ) 6} + N2O(g) T Z-[FeO]+(cis-(NO)2){M ) 6} ∆H80 ) 24.4 K80, bar-1 2.43× 10-16 4.46× 10-15 4.07× 10-14

E80q ) 28.2 A80, s-1 bar-1 2.55× 106 3.08× 106 3.65× 106

k80, s-1 bar-1 1.39× 10-4 4.91× 10-3 7.33× 10-2

E-80q ) 4.5 A-80, s-1 2.45× 1013 2.76× 1013 3.01× 1013

k-80, s-1 5.72× 1011 1.10× 1012 1.80× 1012

81. Z-[FeO]+(cis-(NO)2){M ) 6} T Z-[FeO]+(ON){M ) 5} + NO(g) ∆H81 ) -6.1 K81, bar 3.40× 1012 1.70× 1012 9.85× 1011

E81q ) 9.2 A81, s-1 4.78× 1013 5.62× 1013 6.40× 1013

k81, s-1 2.18× 1010 7.69× 1010 2.00× 1011

E-81q ) 16.6 A-81, s-1 bar-1 7.02× 103 6.82× 103 6.87× 103

k-81, s-1 bar-1 6.40× 10-3 4.54× 10-2 2.03× 10-1

82. Z-[FeO]+(ON){M ) 5} T Z-[FeO]+{M ) 6} + NO(g) ∆H82 ) 3.3 K82, bar 2.60× 104 4.01× 104 5.41× 104

E82q ) 4.8 A82, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k82, s-1 2.28× 1011 4.72× 1011 8.28× 1011

E-82q ) 0.0 A-82, s-1 bar-1 8.78× 106 1.17× 107 1.53× 107

k-82, s-1 bar-1 8.78× 106 1.17× 107 1.53× 107

83. Z-[ONOFeO]+{M ) 5} + N2O(g) T ∆H83 ) 22.2 K83, bar-1 5.95× 10-14 8.33× 10-13 6.22× 10-12

Z-[FeONO]+(cis-(NO)2){M ) 5} E83q ) 23.8 A83, s-1 bar-1 4.06× 107 5.31× 107 6.71× 107

k83, s-1 bar-1 8.37× 10-2 1.91× 100 2.05× 101

E-83q ) 3.2 A-83, s-1 2.07× 1013 2.29× 1013 2.48× 1013

k-83, s-1 1.41× 1012 2.29× 1012 3.30× 1012

84. Z-[FeONO]+(cis-(NO)2){M ) 5} T ∆H84 ) -3.0 K84, bar 1.02× 1010 7.42× 109 5.69× 109

Z-[FeONO]+(ON){M ) 4} + NO(g) E84q ) 6.1 A84, s-1 2.59× 1013 2.94× 1013 3.25× 1013

k84, s-1 1.51× 1011 3.59× 1011 6.89× 1011

E-84q ) 9.7 A-84, s-1 bar-1 4.92× 104 5.05× 104 5.31× 104

k-84, s-1 bar-1 1.48× 101 4.83× 101 1.21× 102



T (K)

reactionEq,a ∆Hb


85. Z-[FeONO]+(ON){M ) 4} T Z-[FeONO]+{M ) 5} + NO(g) ∆H85 ) 0.04 K85, bar 8.65× 104 9.01× 104 9.05× 104

E85q ) 1.7 A85, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k85, s-1 3.12× 1012 4.44× 1012 5.89× 1012

E-85q ) 0.0 A-85, s-1 bar-1 3.61× 107 4.93× 107 6.51× 107

k-85, s-1 bar-1 3.61× 107 4.93× 107 6.51× 107

86. Z-[OFeO2N]+{M ) 5} + N2O(g) T Z-[FeO2N]+(cis-(NO)2){M ) 5} ∆H86 ) 21.2 K86, bar-1 1.58× 10-13 1.95× 10-12 1.33× 10-11

E86q ) 21.8 A86, s-1 bar-1 4.88× 107 6.48× 107 8.29× 107

k86, s-1 bar-1 5.64× 10-1 1.02× 101 9.24× 101

E-86q ) 2.3 A-86, s-1 2.47× 1013 2.73× 1013 2.95× 1013

k-86, s-1 3.58× 1012 5.22× 1012 6.93× 1012

87. Z-[FeO2N]+(cis-(NO)2){M ) 5} T ∆H87 ) -4.2 K87, bar 1.07× 1011 6.68× 1010 4.58× 1010

Z-[FeO2N]+(ON){M ) 4} + NO(g) E87q ) 7.9 A87, s-1 2.19× 1013 2.51× 1013 2.80× 1013

k87, s-1 2.96× 1010 8.73× 1010 1.98× 1011

E-87q ) 12.9 A-87, s-1 bar-1 1.40× 104 1.40× 104 1.45× 104

k-87, s-1 bar-1 2.77× 10-1 1.31× 100 4.31× 100

88. Z-[FeO2N]+(ON){M ) 4} T Z-[FeO2N]+{M ) 5} + NO(g) ∆H88 ) 0.8 K88, bar 1.09× 105 1.25× 105 1.34× 105

E88q ) 2.3 A88, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k88, s-1 1.76× 1012 2.72× 1012 3.84× 1012

E-88q ) 0.0 A-88, s-1 bar-1 1.62× 107 2.18× 107 2.86× 107

k-88, s-1 bar-1 1.62× 107 2.18× 107 2.86× 107

89. Z-[OFeO2NO]+{M ) 5} + N2O(g) T ∆H89 ) 17.2 K89, bar-1 4.73× 10-12 3.65× 10-11 1.74× 10-10

Z-[FeO2NO]+(cis-(NO)2){M ) 5} E89q ) 18.0 A89, s-1 bar-1 4.92× 107 6.55× 107 8.40× 107

k89, s-1 bar-1 1.41× 101 1.61× 102 1.04× 103

E-89q ) 2.4 A-89, s-1 2.29× 1013 2.55× 1013 2.76× 1013

k-89, s-1 2.97× 1012 4.42× 1012 5.96× 1012

90. Z-[FeO2NO]+(cis-(NO)2){M ) 5} T ∆H90 ) -5.0 K90, bar 1.24× 1011 7.08× 1010 4.54× 1010

Z-[FeO2NO]+(ON){M ) 4} + NO(g) E90q ) 7.4 A90, s-1 1.60× 1013 1.80× 1013 1.99× 1013

k90, s-1 3.26× 1010 8.92× 1010 1.91× 1011

E-90q ) 13.2 A-90, s-1 bar-1 1.65× 104 1.63× 104 1.67× 104

k-90, s-1 bar-1 2.62× 10-1 1.26× 100 4.20× 100

91. Z-[FeO2NO]+(ON){M ) 4} T Z-[FeO2NO]+{M ) 5} + NO(g) ∆H91 ) 0.8 K91, bar 1.03× 105 1.18× 105 1.27× 105

E91q ) 2.4 A91, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k91, s-1 1.61× 1012 2.52× 1012 3.58× 1012

E-91q ) 0.0 A-91, s-1 bar-1 1.57× 107 2.14× 107 2.82× 107

k-91, s-1 bar-1 1.57× 107 2.14× 107 2.82× 107

92. Z-[OFeOH]+{M ) 5} + N2O(g) T Z-[FeOH]+(cis-(NO)2){M ) 5} ∆H92 ) 22.2 K92, bar-1 5.03× 10-14 7.00× 10-13 5.21× 10-12

E92q ) 24.6 A92, s-1 bar-1 1.18× 107 1.60× 107 2.08× 107

k92, s-1 bar-1 1.33× 10-2 3.42× 10-1 4.03× 100

E-92q ) 4.3 A-92, s-1 9.79× 1012 1.08× 1013 1.16× 1013

k-92, s-1 2.65× 1011 4.88× 1011 7.74× 1011

93. Z-[FeOH]+(cis-(NO)2){M ) 5} T ∆H93 ) 0.9 K93, bar 3.25× 108 3.72× 108 4.03× 108

Z-[FeOH]+(ON){M ) 4} + NO(g) E93q ) 8.5 A93, s-1 7.34× 1012 8.14× 1012 8.83× 1012

k93, s-1 5.96× 109 1.83× 1010 4.25× 1010

E-93q ) 8.5 A-93, s-1 bar-1 2.30× 104 2.22× 104 2.22× 104

k-93, s-1 bar-1 1.84× 101 4.91× 101 1.05× 102

94. Z-[FeOH]+(ON){M ) 4} T Z-[FeOH]+{M ) 5} + NO(g) ∆H94 ) -0.1 K94, bar 1.01× 106 1.04× 106 1.04× 106

E94q ) 1.5 A94, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k94, s-1 3.70× 1012 5.14× 1012 6.69× 1012

E-94q ) 0.0 A-94, s-1 bar-1 3.67× 106 4.94× 106 6.46× 106

k-94, s-1 bar-1 3.67× 106 4.94× 106 6.46× 106

95. Z-[OFeO]+{M ) 6} + NO2(g) T Z-[OFeO]+(NO2){M ) 5} ∆H95 ) -2.0 K95, bar-1 1.41× 10-7 1.09× 10-7 9.28× 10-8

E95q ) 6.6 A95, s-1 bar-1 1.74× 105 2.13× 105 2.56× 105

k95, s-1 bar-1 6.61× 102 1.79× 103 3.91× 103

E-95q ) 10.0 A-95, s-1 2.03× 1013 2.15× 1013 2.25× 1013

k-95, s-1 4.69× 109 1.64× 1010 4.21× 1010

96. Z-[OFeO]+(NO2){M ) 5} T Z-[OFeO2]+{M ) 4} + NO(g) ∆H96 ) 12.2 K96, bar 6.31× 103 2.82× 104 8.49× 104

E96q ) 12.0 A96, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k96, s-1 5.09× 108 2.52× 109 8.50× 109

E-96q ) 0.0 A-96, s-1 bar-1 8.07× 104 8.92× 104 1.00× 105

k-96, s-1 bar-1 8.07× 104 8.92× 104 1.00× 105

97. Z-[OFeONO]+{M ) 5} + NO2(g) T Z-[OFeONO]+(NO2){M ) 6} ∆H97 ) -1.8 K97, bar-1 9.32× 10-7 7.29× 10-7 6.31× 10-7

E97q ) 6.8 A97, s-1 bar-1 9.95× 105 1.28× 106 1.62× 106

k97, s-1 bar-1 3.30× 103 9.62× 103 2.23× 104

E-97q ) 10.7 A-97, s-1 2.81× 1013 2.90× 1013 2.98× 1013

k-97, s-1 3.54× 109 1.32× 1010 3.53× 1010

98. Z-[OFeONO]+(NO2){M ) 6} T Z-[O2FeONO]+{M ) 5} + NO(g) ∆H98 ) 12.3 K98, bar 5.60× 103 2.54× 104 7.70× 104

E98q ) 12.4 A98, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k98, s-1 3.65× 108 1.89× 109 6.62× 109

E-98q ) 0.0 A-98, s-1 bar-1 6.51× 104 7.45× 104 8.59× 104

k-98, s-1 bar-1 6.51× 104 7.45× 104 8.59× 104


References and Notes(1) Kapteijn, F.; Rodriguez-Mirasol, J.; Moulijn, J. A.Appl. Catal., B

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(2) Mul, G.; Perez-Ramı´rez, J.; Kapteijn, F.; Moulijn, J. A.Catal. Lett.2001, 77, 7.

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T (K)

reactionEq,a ∆Hb


99. Z-[OFeO2N]+{M ) 5} + NO2(g) T Z-[OFeO2N]+(NO2){M ) 6} ∆H99 ) -2.9 K99, bar-1 6.22× 10-5 4.30× 10-5 3.39× 10-5

E99q ) 5.1 A99, s-1 bar-1 1.21× 107 1.63× 107 2.13× 107

k99, s-1 bar-1 1.70× 105 4.22× 105 8.67× 105

E-99q ) 10.3 A-99, s-1 1.56× 1013 1.63× 1013 1.68× 1013

k-99, s-1 2.73× 109 9.81× 109 2.56× 1010

100. Z-[OFeO2N]+(NO2){M ) 6} T Z-[O2FeO2N]+{M ) 5} + NO(g) ∆H100 ) 16.8 K100, bar 1.18× 101 9.12× 101 4.13× 102

E100q ) 16.9 A100, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k100, s-1 8.48× 106 7.53× 107 3.94× 108

E-100q ) 0.0 A-100, s-1 bar-1 7.19× 105 8.25× 105 9.54× 105

k-100, s-1 bar-1 7.19× 105 8.25× 105 9.54× 105

101. Z-[OFeO2NO]+{M ) 5} + NO2(g) T Z-[OFeO2NO]+(NO2){M ) 6} ∆H101 ) -6.8 K101, bar-1 2.91× 10-3 1.25× 10-3 6.89× 10-4

E101q ) 1.2 A101, s-1 bar-1 1.91× 107 2.56× 107 3.31× 107

k101, s-1 bar-1 7.24× 106 1.11× 107 1.60× 107

E-101q ) 10.3 A-101, s-1 1.45× 1013 1.51× 1013 1.55× 1013

k-101, s-1 2.49× 109 8.92× 109 2.32× 1010

102. Z-[OFeO2NO]+(NO2){M ) 6} T Z-[O2FeO2NO]+{M ) 5} + NO(g) ∆H102 ) 17.4 K102, bar 1.15× 101 9.58× 101 4.58× 102

E102q ) 17.5 A102, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k102, s-1 5.44× 106 5.15× 107 2.83× 108

E-102q ) 0.0 A-102, s-1 bar-1 4.73× 105 5.38× 105 6.17× 105

k-102, s-1 bar-1 4.73× 105 5.38× 105 6.17× 105

103. Z-[HOFeO]+{M ) 5} + NO2(g) T Z-[HOFeO]+(NO2){M ) 6} ∆H103 ) -1.4 K103, bar-1 1.90× 10-5 1.56× 10-5 1.41× 10-5

E103q ) 6.9 A103, s-1 bar-1 1.12× 107 1.55× 107 2.08× 107

k103, s-1 bar-1 3.50× 104 1.11× 105 2.76× 105

E-103q ) 10.9 A-103, s-1 1.67× 1013 1.75× 1013 1.82× 1013

k-103, s-1 1.84× 109 7.12× 109 1.96× 1010

104. Z-[HOFeO]+(NO2){M ) 6} T Z-[HOFeO2]+{M ) 5} + NO(g) ∆H104 ) 12.2 K104, bar 2.56× 102 1.14× 103 3.40× 103

E104q ) 12.3 A104, s-1 1.25× 1013 1.46× 1013 1.67× 1013

k104, s-1 4.13× 108 2.11× 109 7.27× 109

E-104q ) 0.0 A-104, s-1 bar-1 1.61× 106 1.85× 106 2.14× 106

k-104, s-1 bar-1 1.61× 106 1.85× 106 2.14× 106

a Calculated activation energy including zero-point energy correction.b Calculated enthalpy averaged over 600-800 K. c The numbers presentedin refs 21 and 22 for this reaction are wrong.

TABLE 2: Norm of the Gradient Difference at the Point of Spin-Surface Crossing and Thermally Averaged Landau-ZenerTransition Probabilities at a Temperature of 600, 700, and 800 Ka

PLZ (H12 ) 395 J/mol) PLZ (H12 ) 825 J/mol)

reaction

|grad(E1) -grad(E2)|

(kJ/mol/Å)T )

600 KT )

700 KT )

800 KT )

600 KT )

700 KT )

800 K

1. Z-[FeO]+{M ) 6} + NO(g) T Z-[FeONO]+{M ) 5} 0.446 0.992 0.990 0.988 1.000 1.000 1.0003. Z-[FeO]+{M ) 6} + NO(g) T Z-[FeO2N]+{M ) 5} 0.446 0.992 0.990 0.988 1.000 1.000 1.0005. Z-[FeO]+{M ) 6} + NO(g) T Z-[OFeNO]+{M ) 5} 0.446 0.992 0.990 0.988 1.000 1.000 1.0006. Z-[FeO2]+{M ) 6} + NO(g) T Z-[FeOONO]+{M ) 5} 141 0.070 0.066 0.062 0.205 0.195 0.1867. Z-[FeOONO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) 1.47 0.906 0.893 0.882 0.998 0.998 0.9978. Z-[OFeO]+{M ) 6} + NO(g) T Z-[OFeONO]+{M ) 5} 514 0.026 0.025 0.024 0.086 0.081 0.0779. Z-[OFeONO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) 1.47 0.906 0.893 0.882 0.998 0.998 0.99710. Z-[OFeO]+{M ) 6} + NO(g) T Z-[OFeO2N]+{M ) 5} 514 0.026 0.025 0.024 0.086 0.081 0.07711. Z-[OFeO2N]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) 1.47 0.906 0.893 0.882 0.998 0.998 0.99712. Z-[OFeO]+{M ) 6} + NO(g) T Z-[FeO2NO]+{M ) 5} 514 0.026 0.025 0.024 0.086 0.081 0.07713. Z-[FeO2NO]+{M ) 5} T Z-[FeO]+{M ) 6} + NO2(g) 1.47 0.906 0.893 0.882 0.998 0.998 0.99720. Z-[O2FeONO]+{M ) 5} T Z-[O2FeONO]+{M ) 7} 454 0.034 0.032 0.030 0.108 0.102 0.09734. Z-[O2FeO2N]+{M ) 5} T Z-[O2FeO2N]+{M ) 7} 164 0.072 0.068 0.064 0.211 0.201 0.19248. Z-[O2FeO2NO]+{M ) 5} T Z-[O2FeO2NO]+{M ) 7} 185 0.065 0.061 0.058 0.192 0.182 0.17451. Z-[OFeO2NO]+{M ) 5} T Z-[OFeO]+{M ) 6} + NO2(g) 1.05 0.953 0.945 0.937 1.000 1.000 0.99957. Z-[Fe(OH)2]+(NO){M ) 7} T Z-[Fe(OH)2]+(NO){M ) 5} 1.87 0.671 0.742 0.725 0.981 0.977 0.97368. Z-[O2FeOH]+{M ) 5} T Z-[O2FeOH]+{M ) 7} 129 0.082 0.078 0.074 0.237 0.225 0.21576. Z-[OFeOH2]+(NO2){M ) 5} T Z-[OFeOH2]+(NO2){M ) 7} 10.1 0.399 0.382 0.367 0.771 0.752 0.73682. Z-[FeO]+(ON){M ) 5} T Z-[FeO]+{M ) 6} + NO(g) 0.446 0.992 0.990 0.988 1.000 1.000 1.00085. Z-[FeONO]+(ON){M ) 4} T Z-[FeONO]+{M ) 5} + NO(g) 11.7 0.400 0.383 0.368 0.772 0.753 0.73788. Z-[FeO2N]+(ON){M ) 4} T Z-[FeO2N]+{M ) 5} + NO(g) 5.92 0.567 0.546 0.529 0.907 0.894 0.88391. Z-[FeO2NO]+(ON){M ) 4} T Z-[FeO2NO]+{M ) 5} + NO(g) 12.4 0.381 0.364 0.350 0.751 0.732 0.71594. Z-[FeOH]+(ON){M ) 4} T Z-[FeOH]+{M ) 5} + NO(g) 2.14 0.815 0.797 0.782 0.991 0.988 0.985

a Landau-Zener probabilities are calculated for spin-orbit coupling energies ofH12 ) 395 and 825 J/mol. The reaction numbers are the sameas those in Table 1.


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nitrous oxide decomposition over fe-zsm-5 in the presence of nitric oxide: a comprehensive dft study

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