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FUNDAMENTAL UNDERSTANDINGOF SELECTIVE HYDROGENATIONS

Núria López

Hydrogenations: at the basis of catalysis

Activity is important but SELECTIVITY is mandatory

What can we do?

ATOMISTIC

ENGINEERING

THERMODYNAMICS

Predict structure solids

Thermodynamics of processesMost-likely configurations under rx

Reaction pathsKinetics processes

Most-likely configurations under rx

Store and search for dataIdentify structure-activity correlations

Assess stabilityIn-silico Design systems with specific properties

KINETICS

Gold chemistry and hydrogenation

353 K0.2 wt.% Pd/Al2O3

X

S

X(C3H4)

S(C3H6)

C3H4:H2:He = 5:15:80

J. Catal. 247, 383 (2007)

0.49

0.63

General descriptor thermodynamic selectivity

F. Studt, F. Abild-Pedersen, T. Bligaard, R. Z. Sørensen,C. H. Christensen, J. K. NørskovScience , 320 1320(2008)

Industrial problem: Alkyne hydrogenation

Cracking reactions

Fuelgas

SteamCracking

or otherOlefin

Sources

Hydrogen

Selective Hydrogenation

Selective Hydrogenation

C2

C3

Dimerization

Oligomerization

Metathesis

1-Butene

Alpha-olefins

Ethene

Propene

2-Butenes

over-hydrogenation oligomerisation

Pd (0.04%)/ δ-Al2O3

T 350 Kp 20 bar

CO feeding (50-500 ppm)Salkenes

Hydrogenations: the problem

Hydrogenation: Reaction mechanism

Horiuti, J. and Polanyi, M. , Trans. Faraday Soc. 30, 1164 (1934)

Alkyne hydrogenation: Pd catalyst

Pd (0.04%)/ Al2O3 Experimental evidence

Salkenes

Pretreatment

State of Pd

Self-consistently analyze composition activity

X, Salkenes

pH2

pCO

pC2H2

Hydride formation

pH2

Greeley, et al. ACIE, 43, 4296 (2004)

-Hydride phase formation: BET equivalence

•The adsorption takes place on a lattice •First adsorbate layer is adsorbed on the solid surface•Second adsorbate layer is adsorbed on the first •Adsorption enthalpy first layer and then for other layers

pH2

Upt

ake

1

Hydride formation

Pd hydride

E ads -0.5 eV/atom1 ML

E ads -0.1 eV/atom

Pretreatment and State of Pd

pH2

Carbide formation

Pretreatment State of Pd

carbide

p alkynes

Teschner et al. Science 320, 86 (2008) Teschner, Sautet, ACIE (2008)

Carbide formation


carbide

p alkynes

2.12 vs. 1.69

Dehydrogenations are lower in energyC-C splitting lower at steps

Andersin, et al. JPCC 113, 8278 (2009); Surf. Sci. 604, 762 (2010)

<1.5 eV

Carbide formation

0.8-1.0 eVCCC


carbide

p alkynes

•Lateral repulsion between C atoms is very large no dense phases PdC0.13•Preferential decoration of corners and steps, due to high formation energies at surfaces•Near surface carbides, mostly•Ability to be formed depends on the alkyne-alkene pair

García-Mota, et al. J. Catal. 273, 92 (2010)

Hydride formation in the presence of carbide

carbide

palkynes

Hydride formation

1ML

Carbide prevents

hydride formation


Alkyne hydrogenation: Pd catalyst

Industrial conditionsPd (0.04%)/ δ-Al2O3

T 350 Kp 20 bar

continuous CO feeding (50 < CO < 500 ppm)

CO covered Pd surface

p CO


Hydride formation

Very dense layers

E ads -1.43 eV/atom

( p(2x2)-3CO ) CO prevents

hydride formation

Role of CO: hydride formation

Reaction paths and kinetic contributions

Horiuti, J. and Polanyi, M. , Trans. Faraday Soc. 30, 1164 (1934)

Kinetics pure Pd(111)

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.82 eV

Pd clean surface

Eads-2.02 eV

0.66

0.81 0.79

0.74 0.79

0.45

ts ts

0.81 0.79

50% 50%

vinyl

ethene ethylidene

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.15eV

Experimental evidence

p H2 pretreatmentEads‐0.94eV p = 1 bar

T = 348K

Pd /γ-Al2O3

Pd hydride

Kinetics -PdH

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.15 eV

0.58

0.36 0.06

0.75

PdH inducesEads

-0.94 eVPd hydride

Kinetics b-PdH

Experimental evidence

p H2 pretreatment

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.67 eV

0.70

0.57 0.69

0.89 0.57

Carbide

Carbide inducesEads

-1.49 eV

Kinetics Carbide phase

Experimental evidencep H2 pC2H2pretreatment

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.00eV

0.45

0.14 0.23

0.44 0.57

0.20

Eads‐1.24eV

Kinetics CO phase

CO covered

ethyne

vinyl

ethyl

ethylidene

ethane

ethene

Edes0.00 eV

0.45

0.14 0.23

0.44 0.57

CO covered

0.20

p C2H2 p H2

CO inducesEads

-1.24 eVp CO

p CO

Experimental evidencepretreatment

Kinetics CO phase

Oligomerization

Ea =1.38 eVEa(+CO) =1.40 eV

Reduction of ensembles

Oligomerization

Ea =1.38 eVEa(+CO) =1.40 eV

Reduction of ensembles

X

1. Thermodynamic selectivity Blocks subsequent reactions2. No active subsurface species Blocks overhydrogenation3. Small ensembles Reduces oligomerization

Requirements for a good hydrogenation catalyst

Carbide:Fulfills (1-3)LabileDifficult homogeneously


Hydride:Fulfills (1) and (3)

CO phase:Fulfills (1-3)RobustEasily homogeneousOverwrites the state of the catalyst

Hydrogenations: Technical solution

Molecular Modifier

Secondary metal

Active metal

Role of co-catalyst

Lopez, Vargas-Fuentes Chem. Comm.48, 1379 (2012)

Complex substrates on Pd

Bridier et al. ChemCatChem 4, 1420 (2012)

1. Thermodynamic selectivity2. Inability to form active subsurface

species3. Definition of small ensembles

Organic synthesis: Pd Lindlar Catalyst (1952)

Selective for MultifunctionalizedAcetylenic molecules (Solvent)

Vitamin A (Retinol)

BaSO4 +Pd Pd/BaSO4 +Pb(AcO)295ºC

Pb-Pd/BaSO4+

Lindlar Catalyst

N

Comparison between Pd catalysts

Hydrorefining Catalyst Lindlar Catalyst

Substrate Ethyne, propyne Long chain alkynes

Medium Gas phase or liquid phase Liquid phase

Pd content 0.01 – 0.05 % 1 – 5 %Second metal Ag, Au, etc. Pb, Bi, Cu

Selectivity modifier CO Quinoline

Support Al2O3 CaCO3, BaSO4

Temperature RT – 350 K RT

Solvent None Benzene, Toluene, Methanol

Regioselectivity --- Cis

PH2 Up to 20 bar 1 – 10 bar

Operation Continuous Batch

Lindlar preparation: I

Lindlar preparation: II

Pb(AcO)2 95ºC

Eisl

Formation of Pb islands

Unfavourable

Lindlar preparation: III

N

Santarosa, Iannuzzi, Vargas, Baiker, ChemPhysChem 9, 401 (2008)

Lindlar Tiling

Jujol, Gaudi 1906

Lindlar Tiling

Thermodynamic selectivity Blocks subsequent reactions

Lindlar Tiling

Inability to form hydride Achieved by tiles (solvent)

Lindlar Tiling

Definition of small ensembles Reduces oligomerization

Garcia-Mota et al. TCA 128, 663 (2011)

New generation catalyst: supported colloids

Witte, Patent NL50039, 2009 Witte et al., ChemCatChem 5, 582 (2013)

▶ Conventional technique

Difficult to scale up Low-boiling point compounds Centrifugation required

Preparation of ligand-modified catalysts

Easy to scale up No centrifugation required Versatile

metalprecursor H2O solvent NaBH4PVP

metalprecursor H2O

carrier(C, TiSi2O6)

HHDMA

▶ NanoSelectTM technology

The structure: TEM

Comparison between Pd catalystsHydrorefining

Catalyst NanoSelectTM Lindlar Catalyst

Substrate Ethyne, propyne Terminal alkynes Long chain alkynes

Medium Gas phase or liquid phase Liquid phase Liquid phase

Pd content 0.01–0.05 % 0.1-0.5% 1 – 5 %Second metal Ag, Au, etc. Pb, Bi, Cu

Selectivity modifier CO HHDMA Quinoline

Support Al2O3 TiS CaCO3, BaSO4

Temperature RT – 350 K RT RT

Solvent NoneBenzene, Toluene Benzene, Toluene,

Methanol

PH2 Up to 20 bar 1 – 10 bar 1 – 10 bar

Operation Continuous Continuous Batch

State-of-the-art alkyne hydrogenation catalyst BASF

Lindlar, Helv. Chim. Acta 1952, 35, 446 Blaser et al., ChemCatChem 2009, 1, 210

Pb

ensemble

selective unselective

Pd, Pt

▶ Lindlar Drawbacks: Poor metal utilization Lead as a modifier

C20

tail

PO4

met

al

500 700 900

Wei

ght l

oss /

%

T / K

0

10

500 600 700

200 220 240

Inte

nsity

/ a.

u.

m/e / -

ToF-SIMS

31P MAS NMRCryo-TEM

TGA

metal-O-P

50 nm-100 0 100

Inte

nsity

/ a.

u.

/ ppm

-PO4

Structure of the ligand-modified catalyst

The interface structure

0 5 10 15 200

20

40

60

80

100Fr

eque

ncy

/ %

dPd / nm0 5 10 15 20

0

20

40

60

80

100

Freq

uenc

y / %

dPt / nm

0 5 10 15 200

20

40

60

80

100

Freq

uenc

y / %

dPt / nm0 5 10 15 20

0

20

40

60

80

100

Freq

uenc

y / %

dPd / nm

palladium platinum

D = 6%

D = 17%

D = 8%

D = 49%231 m2 g–1 234 m2 g–1

4 m2 g–110 m2 g–1

10 nm

Chem. Eur. J. 2014, 20, 5926 ACS Catal. 2015, 5, 3767

Textural and compositional characterization

5 wt.% Pd or Pt1-4 wt.% Pb/CaCO3

0.5 wt.% Pd or PtHHDMA/C

0 20 40 60 80 10080

90

100

S(C

6H12

)/ %

X(C6H10) / %

Wcat = 0.1 g, T = 30°C, P = 1 barF(H2) = 18-36 cm3 min-1

F(C6H10+solv.) = 0.3-3 cm3 min-1

alkyne

t = 0 ps t = 0.5 ps t = 1 ps

▶ 1-hexyne hydrogenation

Pd-HHDMA in alkyne hydrogenation

Chem. Eur. J. 20, 5926 (2014)

Pd-PbPd-HHDMA Pd Eads(C2H2) = -1.6 eVEads(C2H4) = -1.2 eV

Eads(C2H2) = -0.8 eVEads(C2H4) = -0.2 eV

Eads(C2H2) = -0.9 eVEads(C2H4) = -0.4 eV

Pd-Pb

Pd-HHDMA

▶ Classical MD simulations

▶ DFT calculations over Pd(111)

-4

-3

-2

-1

0

1

Reaction coordinate

E /

eV

Pt-HHDMA in nitroarene hydrogenation

Facile -NO2 adsorption and H2 activation enhance the activity of Pt-HHDMA

ACS Catal. 2015, 5, 3767

reactant product

Pt-Pb

Pt-HHDMA

Pt-HHDMA Pt-Pb

4

5

TOF(4-chloronitrobenzene hydrogenation) / 103 h-1

1

23

45

Wcat = 0.1 g, F(H2) = 18 cm3 min-1, F(C6H10+solv.) = 0.3 cm3 min-1

All strategies are based on

Large amount of Pd

Poisoned in some way

Is it possible to use the minimum ensemble without poisoning

mpg-C3N4 support

G. Vilé, D. Albani, M. Nachtegaal, Z. Chen, D. Dontsova, M. Antonietti, N. López, J. Pérez-RamírezAngew. Chem., Int. Ed. 2015, doi: 10.1002/anie.201505073R1

Single site hydrogenation catalyst


Active 1-hexyne

Selective

Stable

Single site hydrogenation catalyst


Active 1-hexyne•mechanism as homogeneous PdSelective•thermodynamic selectivityStable•low Pd concentration in pores

Conclusions

•Integration of DFT and experiments is crucial tounderstand the chemistry

•The strategies in Pd chemistry for hydrogenationare the same independently application

•Reduction of the catalyst to smallest ensemble ispossible

AcknowledgementsM. Garcia-MotaG. Novell-LeruthC. Vargas-FuentesL. BellarosaN. Almora-Barrios

Experimental Collaborations

Prof. J. Pérez-Ramírez (ETH)G. Vilé

CeO2: Oxygen Vacancy formation

CeO2 is able to reversible adsorb O2 in volume

Bulk vacancies more stable than surface ones

Huang et al. Sol. State. Sci. (2005)Lindemer and Brynestad, J. Am. Ceram. Soc. (1986)

CeO2: STM images localization and islanding

Annealing 900ºC 5 min

Esch et al. Science (2005)

CeO2 vs. RuO2

RuO2 CeO2

↑↑↑↑ ↑↑2D 2D-3D

Cl*+Cl*→Cl2+2* Cl# +Cl*→Cl2+#+*

O2 adsorption O2 adsorption

> 1 Hydride Pd


Role of the molecular modifier

Continuous CO feeding (50 < CO < 500 ppm)

pictures

Rose, et al. Surf. Sci. 512, 48 (2002)

Reaction paths: Thermodynamic factor

Segura, Lopez and Pérez-Ramírez, J. Catal. 247, 383 (2007); Lopez et al. JPCC 112, 9346 (2008); Studt et al., Science, 320, 1320 (2008)

X

BEP-relationships

Activation and reaction energiesare linked by a BEP-likerelationship

Activity of Colloidal Pd, Pt nanoparticles

66

Chemical applications

Pd Pd-CO Ni Au Cu0.0

0.2

0.4

0.6

0.8

1.0

X,Y

/ -

Catalytic systems

Y(C3H6)

Y(C3H8)Y(oligomers)

Alternative systems

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

M-C 3H 6TS 2TS 1

M-H-C 3H 5

M-2H-C 3H 4

M-2H+C 3H 4TS H2

M+H 2+C 3H 4

C3H4

E, e

V

Au Cu Pd Ni

C3H6

Cu can be attractive under some conditions but … requires higher T and generates more oligomers

Bridier, et al. J. Catal 269, 80 (2010); Dalton Transac. 39, 8412 (2010)

Carbide exclusion area


carbide

p alkynes


•Large exclusion areasaround C species

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