ammoxidation of propane over v-sb and v-sb-nb mixed oxides

www.elsevier.com/locate/apcata

Applied Catalysis A: General 298 (2006) 1–7

Ammoxidation of propane over V-Sb and V-Sb-Nb mixed oxides

M.O. Guerrero-Perez 1, M.V. Martınez-Huerta 2, J.L.G. Fierro, M.A. Banares *

Instituto de Catalisis y Petroleoquimica, CSIC, Marie Curie 2, E-28049-Madrid, Spain

Received 15 July 2005; received in revised form 7 September 2005; accepted 15 September 2005

Available online 3 November 2005

Abstract

Pure VSbO4 phase is not active for propane ammoxidation, unless some segregated a-Sb2O4 is present on its surface. Surface vanadium may be

necessary to activate propane. For the ternary Sb-V-Nb oxide catalysts: Sb-V-O, Nb-V-O and Sb-Nb-O phases may form. SbNbO4 is inert and forms

at the expense of efficient Sb-V-O and V-Nb-O phases. The extent of formation of these phases strongly depends on the preparation method. The Sb

precursor determines if V-Sb or Nb-Sb is the preferred interaction. Tuning the interaction of Sb with the other elements affects the catalyst structure

and performance.

# 2005 Elsevier B.V. All rights reserved.

Keywords: V-Sb-Nb-O; V-Sb-O; Oxidation; Ammoxidation; Propane; Acrylonitrile; Structure–activity relationship; In situ Raman; XRD

1. Introduction

Acrylonitrile has been industrially produced from propylene

as an important intermediate for the preparation of fibers,

important polymers as styrene–acrylonitrile, acrylonitrile–

butadiene–styrene, and other valuables chemicals [1]. The

direct conversion of propane into acrylonitrile by reaction with

oxygen and ammonia is an alternative route to the conventional

propylene ammoxidation since propylene is typically more

expensive than propane. The economic implications of this new

route are very important, but the activation of propane is the

limiting step [2]. Since the adsorption rate of propane is near ten

times smaller than that of propylene [3] the conversion of

propane is at least ten times smaller than propylene [4]. In

addition, the reaction conditions to activate the C–H bond in

propane are more energy demanding, which has a negative

effect on selectivity.

There are several studies about the catalysts used for

propane ammoxidation, but most of the works concentrate on

two types of catalysts [1,5]: the antimonates with rutile

* Corresponding author. Tel.: +34 91 585 4788; fax: +34 91 585 4760.

E-mail address: [email protected] (M.A. Banares).1 Actual address: Departamento de Ingenierıa Quımica, Universidad de

Malaga, Campus de Teatinos, E-29071-Malaga, Spain.2 Actual address: Departamento de Quımica Fısica, Universidad de La

Laguna, c/Astrofısico Francisco Sanchez s/n, E-38071 La Laguna, Tenerife,

Spain.

0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcata.2005.09.013

structure [6,7] and the molybdates [1–18]. Both catalyst

systems usually incorporate vanadium as an essential ingre-

dient. Mo-V catalysts modified with Nb and Te may afford near

50% yield to acrylonitrile [2] and acrylonitrile yields of 60%

have been reported for the antimonates system [9]. Despite the

large relevance of these catalysts, the nature of the active site is

still not fully understood. Sb-V-O catalysts with an excess of V

are highly active and selective for propane oxidative

dehydrogenation (ODH) while an excess of Sb affords Sb-V-

O catalysts that are more efficient for propane ammoxidation

[19].

Several preparation methods have been reported for the Sb-V-

O-based catalysts and it is concluded that the preparation method

has an important effect on the structure and on the performance

[12,20,21]. The methods most usually studied correspond to

patents filed in 1988 by Standard Oil Co. [9–11] and it consists on

keeping in reflux during several hours an aqueous suspension of

NH4VO3 or V2O5 and Sb2O3. Others studies use solutions of V4+

in oxalic acid to which antimonic acid is added [22] or even

prepare catalysts with a solution of VCl3 and SbCl5 on HCI

[8,23]. Brazdil et al. have also developed a sol–gel method for

this kind of catalysts [21]. The aim of all these preparation

methods is to provide an intimate contact between Sb5+ and V4+

in order to improve their redox reaction to form VSbO4 phase

[24], which is directly related to acrylonitrile formation

[2,13,19–24], and provides the catalyst with a high specific

area. More recently, mechanical activation has also proved to be

an interesting method to prepare VSbO4 phases [25].

M.O. Guerrero-Perez et al. / Applied Catalysis A: General 298 (2006) 1–72

Grasselli [1,5] reports on ternary mixed metal oxide

catalysts with the formula VSbxMyOz, where M stands for

W [13,26], Te [9,13], Ni [13,27], Mg [13], Nb [13], Sn [28,29],

Bi [30], Al [26,32,33], Fe [34], and Ti [35], among others.

Usually the metal M forms a solid solution with the rutile

structure of VSbO4 forming mixed phases with Sb and V, like

Al1�xSbVxOx [32] or Sb0.9V0.9�xWxO4 [26] or V-Sb-Ti-O [58].

Niobium compounds and materials such as niobium pentoxide,

niobic acid, niobium phosphate, and mixed oxides containing

niobia are shown to be useful on catalysis as supports and as

promoters for different reactions [37–41]. Specially, catalysts

containing niobium have been found active in dehydrogenation

reactions [42–44] and the dehydrogenation of propane is

commonly proposed as the first step in propane ammoxidation

[23,45–47], so Nb seems to be a key element on propane

ammoxidation to acrylonitrile, specially mixed oxides contain-

ing Nb (Mo-V-Nb-Te catalysts) have been found active and

selective propane ammoxidation [13,48–50].

A third element may also be present as the cation of an oxide

support. The use of an oxide to support/promote VSbO4 is

particularly interesting, for instance, alumina-supported VSbO4

[31]; it performs like bulk VSbO4 with a more economic

composition [51]. Other supports, like niobia, significantly

promote the performance of VSbO4 [52]. These catalysts are

prepared by impregnation of the oxide support. It would be

desirable to assess direct synthesis of efficient V-Sb-Nb oxide

catalysts for propane ammoxidation. However, the use of

niobia, vanadia and antimony supports may lead to efficient

Nb-promoted Sb-V-O phases or to inert SbNbO4 phases. This

manuscript evaluates the relevance of different precursors on

the preparation of V-Sb-Nb oxide catalysts.

2. Experimental

Bulk Sb-V-O catalysts (SV series) were prepared drying in a

rotatory evaporator at 80 8C NH4VO3 (Sigma) and antimony that

was kept in solution according to a method developed in our

laboratory [49]. The resulting solid was dried at 115 8C for 24 h

and then calcined in air at 660 8C for 12 h and at 750 8C for 24 h.

Four catalysts were prepared SV1, SV3, SV5, and SV7 with Sb/V

molar ratios of 1, 3, 5, and 7, respectively.

Table 1

Precursors used during synthesis, composition and BET area of catalysts

Catalysts Compositiona BET surface area (m2 g�

Sb-V-O catalysts

SV1 VSb 0.6

SV3 VSb3 0.5

SV5 VSb5 0.8

SV7 VSb7 0.6

Sb-V-Nb-O catalysts

SVN1A V0.1Sb0.3Nb0.3 72

SVN1B V0.1Sb0.3Nb0.1 19

SVN2 V0.2Sb0.3Nb0.5 8

SVN3 V0.2Sb0.1Nb0.4 12

a Based on the ICP element analyses.

Sb-V-Nb-O catalysts (SVN series) were prepared with three

different methods. The Method 1 uses an aqueous solution with

SbCb, NH4VO3, and Nb2(C2O4)5 and two catalysts were

prepared SVN1A and SVN1B (Table 1), with different molar

ratios. In this method a solution of Nb2(C2O4)5 [50] was added

to an aqueous solution of an appropriate amount of NH4VO3

and SbCl3 at 60 8C. The solution was kept under stirring for 2 h

at this temperature, and then was separated by centrifugation.

The samples were dried at 120 8C for 12 h and calcined in air at

400 8C for 5 h. The Method 2 uses an organic solution and was

used for the preparation of SVN2 catalyst, a suspension of

Nb2(C2O4)5 in CH2Cl2 was added to a solution of SbCl5 and

(C5O2H8)2VO in CH2Cl2. The solution was stirred at 60 8C for

2 h and the solvent was evaporated. The catalyst powder was

dried at 120 8C for 16 h and calcined in air at 500 8C for 5 h.

Method 3 uses the same molar ratio and methodology than 2,

but Nb2O5 is used as the precursor of Nb, catalyst SVN3 was

prepared according this method.

Raman spectra were run with a single-monochromator

Renishaw System 1000 equipped with a thermoelectrically

cooled CCD detector (�73 8C) and holographic super-Notch

filter. The holographic Notch filter rejects the elastic scattering.

The samples were excited with the 514 nm Ar line; spectral

resolution was ca. 3 cm�1 and the spectrum acquisition time was

300 s. The spectra were obtained under dehydrated conditions

(ca. 390 K) in a hot stage (Linkam TS-1500). Raman spectro-

scopy provides information about the bulk of the material.

X-ray diffraction patterns were recorded on a Siemens

Krystalloflex D-500 diffractometer using Cu Ka radiation

(l = 0.15418 nm) and a graphite monochromator. Working

conditions were 40 kV, 30 mA, and scanning rate of 28 min�1

for Bragg’s angles (2u) from 5 to 708. Nitrogen adsorption

isotherms (�196 8C) were recorded on an automatic Micro-

meritics ASAP-2000 apparatus. Prior to the adsorption

experiments, samples were outgassed at 413 K for 2 h. BET

areas were computed from the adsorption isotherms (0.05 < P/

Po < 0.27), taking a value of 0.164 nm2 for the cross-section of

the adsorbed N2 molecule at �196 8C. ICP analyses were

performed in a 3300 Perkin-Elmer apparatus. Around 100 mg

of sample were dissolved with nitric, chloride, and fluoride

acids in a microware oven.

1) Method Precursors

– NH4VO3, Sb soluble complex




1 SbCl3, NH4VO3, Nb2(C2O4)5

1 SbCl3, NH4VO3, Nb2(C2O4)5

2 SbCl5, (C5O2H8)2VO, Nb2(C2O4)

3 SbCl5, (C5O2H8)2VO, Nb2O5

5

M.O. Guerrero-Perez et al. / Applied Catalysis A: General 298 (2006) 1–7 3

Fig. 1. XRD patterns of fresh Sb-V-O catalysts.

Activity measurements were performed using a conven-

tional microreactor with on-line gas chromatograph equipped

with a flame ionization and thermal conductivity detector. The

correctness of the analytical determinations was checked for

each test by verification that the carbon balance (based on the

propane converted) was within the cumulative mean error of the

determinations (�10%). Tests were made using 0.2 g of sample

with particle dimensions in the 0.25–0.125 mm range. The axial

temperature profile was monitored by a thermocouple sliding

inside a tube inserted into the catalytic bed. Tests were made

using the following feedstock: 25% O2, 9.8% propane, 8.6%

ammonia, and helium balance. The total flow rate was

20 ml min�1 corresponding to a gas-space velocity (GHSV)

near 3000 h�1. The quantity of catalyst and total flow were

determined in order to avoid internal and external diffusion

contributions. Yield and selectivity values were determined on

the basis of the moles of propane feed and products, considering

the number of carbon atoms in each molecule.

3. Results

3.1. Sb-V-O system

Table 1 represents the composition and BET area values for

the Sb-V-O catalysts. The BET area values are quite low for

these catalysts, probably due to the high calcination tempera-

ture. The XRD patterns of the fresh catalyst are displayed in

Fig. 1. SV1 pattern (Sb/V = 1) corresponds to the VSbO4 phase

(JCPDS file 16-0600), the patterns of SV3, SV5, and SV7

catalysts (Sb/V = 3, 5, and 7, respectively) correspond to

VSbO4 and a-Sb2O4 phases (JCPDS file 11-0694 and 32-0042).

The Raman spectra of the fresh and used catalyst are rep-

resented in Fig. 2. The spectrum of the fresh SV1 catalyst pre-

sents a band centered at 880 cm�1, which has been assigned to the

Sb0.92V0.92O4 phase [19]. Theweak Raman band near 1020 cm�1

is not sensitive to humidity, so this band must correspond to

Fig. 2. (A) Raman spectra of fresh and used Sb-V-O catalysts. (B) Sp

the VSbO4 phase and not to surface vanadium oxide species.

However, this band is quite broad, and it is not possible to provide

a conclusive absence of surface vanadium oxide species.

The Raman spectra of catalysts with antimony excess (SV3,

SV5, and SV7) present modes at 190, 255, 372, 451, and

716 cm�1 that correspond to the a-Sb2O4 phase [51], these

bands are very strong while VSbO4 possesses a low Raman

section; therefore, Fig. 2B blows-up the 530–1030 cm�1

window. The weak bands at 610, 650, 710, 749, and

820 cm�1 that correspond to the a-Sb2O4 phase are evident.

Raman spectra of all catalysts with antimony excess show the

bands that correspond to the a-Sb2O4 phase. The SV1, SV3,

and SV5 catalysts exhibit the bands of VSbO4 phase; these

bands are particularly weak for catalyst SV7. The Raman

spectra show no appreciable changes for the used catalysts.

These catalysts exhibit a steady-state operation for at least

20 h. Fig. 3 represents the yields to different products for

ectra between 530 and 1030 cm�1 with a-Sb2O4 reference phase.


Fig. 3. Yields (%) to different products at 500 8C for catalysts SV1, SV3, SV5,

and SV7. Reaction conditions: 20 h time-on-stream, total flow 20 ml min�1,

feed composition (vol.%): C3H8/O2/NH3 (9.8:25:8.6), 200 mg of catalysts.

Fig. 5. Raman spectra of fresh and used Sb-V-Nb-O catalysts.

catalysts SV1, SV3, SV5, and SV7 at 500 8C. The catalyst with

the highest vanadium content (SV1, with Sb/V = 1) is the most

active and presents the highest yield to acrylonitrile; however,

selectivity to acrylonitrile is rather low. Sb excess leads to less

active, but more acrylonitrile selective, catalysts. The catalysts

SV5 is most selective towards acrylonitrile.

3.2. Sb-V-Nb-O system

XRD patterns of fresh and used Sb-V-Nb-O catalysts are

represented in Fig. 4. The catalyst SVN2 presents a diffraction

pattern that corresponds to the phases Nb2O5 (JCPDS 30-0873),

a-Sb2O4 (JCPDS 11-0694), and VSbO4 (JCPDS file 16-0600).

After reaction, the diffraction peaks of VSbO4 become more

intense. Catalyst SVN3 exhibits a pattern quite similar to that of

SVN2, it presents the pattern of Nb2O5 (JCPDS file 7-0061),

while after reaction it presents those of Nb2O5 and a-Sb2O4.

SVN1A is amorphous but it exhibits the pattern of SbNbO4

phase after reaction (Fig. 4) (JCPDS 16-0907). Fresh and used

SVN1B catalyst present the pattern of SbNbO4 and a-Sb2O4

phases, and the diffraction peaks of SbNbO4 become more

intense for the used sample.

Fig. 4. XRD patterns of fresh and used Sb-V-Nb-O catalysts.

Fig. 5 shows the Raman spectra of fresh and used dehydrated

Sb-V-Nb-O catalysts. The Raman spectra of fresh and used

SVN2 and SVN3 are very similar with broad bands near 900,

700, and 200 cm�1, typical of Nb2O5 TT crystalline phase

[52,53]. The Raman spectrum of the fresh SVN1A catalyst

(Fig. 5) shows broad Raman bands that correspond to Nb2O5

phase but after reaction it exhibits Raman bands at 190, 255,

372, and 451 cm�1, typical of a-Sb2O4 phase [51] and features

near 845, 686, and 621 cm�1 that correspond to SbNbO4 phase

[52,53]. Spectra of fresh and used SVN1B catalyst show Raman

bands that correspond to a-Sb2O4 and SbNbO4 phases. Mixed

V-Nb-O phases, if present, could not be observed. These

possess weak Raman bands [54].

Fig. 6. Yields (%) to different products at 500 8C for catalysts SVN2, SVN1A,

SVN1B, and SVN3. Reaction conditions: total flow 20 ml min�1, feed com-

position (vol.%): C3H8/O2/NH3 (9.8:25:8.6), 200 mg of catalysts.


Fig. 6 represents the yields to the different products for

catalysts SVN2, SVN1A, SVN1B, and SVN3, at 500 8C.

Catalyst SVN3 is much more active than SVN2, SVN1A, and

SVN1B, but at 500 8C it is very selective towards propylene

while catalysts SVN2 is the most selective towards acrylonitrile.

4. Discussion

Sb-V-based oxide structures are directly related to propane

ammoxidation reaction. In particular, VSbO4 appears closely

related to efficient catalysts [55]. In excess of Sb, the VSbO4/a-

Sb2O4 system is more selective to acrylonitrile formation. SV1

is active (Fig. 3), to the production of carbon oxides, propylene

and acrylonitrile; the higher activity at lower Sb/Vatomic ratios

is probably related to the higher vanadium content [55–57].

Bulk Sb-V-O samples with Sb/V > 1 are more selective to the

formation of acrylonitrile [1,2,19,55]. Our results are consistent

with those works: samples possessing VSbO4 and a-Sb2O4

phases, like SV3, SV5, and SV7, are more selective to

acrylonitrile formation than the pure VSbO4 phase, as can be

observed in Fig. 3. The excess of Sb renders the Sb-V-O system

more selective; however, total conversion is much lower.

Surface vanadium oxide species, on the other hand, appear

critical to activate propane [49,58]. Surface vanadium oxide

species also activate conversion of propane towards oxidative

dehydrogenation reaction, even in the presence of Sb [58,59].

The effect of Sb/V atomic ratio is not clearly understood yet.

Nilsson et al. [19] have found that the best rate for formation of

acrylonitrile is achieved with catalysts with Sb/V = 2. Centi and

Mazzoli [8] reported catalysts with Sb/V > 1 as the most active

on acrylonitrile formation and Chiang and Lee [60] concluded

that the best activity results are achieved with catalysts with Sb/

V = 1. In general, mixed a-Sb2O4/VSbO4 phases are selective

to acrylonitrile formation; the results presented are in

accordance with this point. However, the origin of these

differences on the Sb/V values may be due to the fact that

surface composition does not usually correspond to the bulk

composition. Obviously, catalytic performance is directly

affected by the surface composition of the catalysts, where

the molecules react. There appears to be a delicate interaction

between segregated Sb oxide, surface vanadium oxide species,

and VSbO4 that renders the system efficient for propane

ammoxidation [49]. It may be due to a cooperative effect

between these phases, as it has been pointed out previously

[19,26]. Operando Raman-GC studies during propane ammox-

idation on supported Sb-V systems suggest that such

cooperation may be due to a migration cycle of Sb5+ species

that facilitate the redox cycle of vanadium species [49,58],

which involves surface V5+ species and lattice V3+ sites in

VSbO4 [49,55].

The interplay between Sb and V for propane ammoxidation

is strongly affected by the presence of a third element

[1,5,9,13,26–36]. Niobia is particularly interesting since many

possible interactions may take place, leading to V-Nb-O, V-Sb-

O, and Sb-Nb-O phases [52,53], some of which are present in

catalysts developed by Mitsubishi [17,18] and by bp [21]. The

V-Nb-O phases are efficient for propane ammoxidation in

niobia-supported vanadia catalysts [52] and SbNbO4 does not

appear active for propane ammoxidation [53].

The bulk V-Sb-Nb-O catalysts have been prepared follow-

ing different preparation methods to differently affect their

structures.

SVN2 and SVN3 are prepared by interaction between

vanadium acetyl acetonate and SbCl5 with different niobium

precursors. They possess similar structures; according to

combined XRD and Raman spectroscopy: VSbO4 and Nb2O5

phases are present, but not SbNbO4. The absence of the VSbO4

diffraction pattern for SVN3, visible to Raman spectroscopy,

must be due to the small size of its domains. Some antimony

remains segregated as a-Sb2O4; which becomes more evident

in used samples. Thus, the trend of antimony to migrate to the

catalysts surface observed with supported Sb-V-O catalysts

[45,51], is also observed in the present work for bulk Sb-V-Nb-

O catalysts. These catalysts perform propane ammoxidation

better that the SV series and the other SVN catalysts. This is

consistent with the beneficial effect of niobia on the

performance reported for VSbO4 [52]. Thus, the presence of

both VSbO4 and Nb2O5 account for the better performance,

compared to SV series.

SVN1A and SVN1B are prepared by interaction between

NH4VO3 and SbCl3 and niobium oxalate. They possess similar

structures, both possess SbNbO4 but not VSbO4 or Nb2O5,

according to Raman spectroscopy (Fig. 5) and XRD patterns

(Fig. 4). The formation of VSbO4 is not observed for SVN1A or

SVN1B (from SbCl3); in these catalysts; antimony reacts

preferentially with niobium. SbNbO4 phase is inert for propane

ammoxidation [52,53]. The presence of SbNbO4 and absence

of VSbO4 accounts for their poor ammoxidation performance.

Apparently, niobia precursor is not critical for Sb-V-Nb

interactions since niobia oxalate may result in either Nb2O5 or

SbNbO4. However, the oxidation state of the antimony chloride

follows a trend: SbCl5 interacts preferentially with vanadia;

SbCl3, with niobia. Using SbCl5, Sb, and V interact forming

mixed phases like VSbO4 and Nb2O5 crystalline phase,

regardless of niobium precursor (SVN2, SVN3). Such interac-

tion is consistent with the redox reaction between Sb5+ and V4+ to

form VSbO4 [21,24]. In these catalysts, the VSbO4 phase

becomes more evident after propane ammoxidation, so this phase

is further formed during reaction. The in situ formation of this

phase during propane ammoxidation has been reported for

alumina-supported Sb-V-O catalysts using operando Raman-GC

methodology [24].

The interaction between Sb, V, and Nb can be tuned by the

oxidation state of antimony chloride. SbCl3 promotes the Sb-

Nb interaction, which leads to SbNbO4. This phase is not active

for propane ammoxidation; but, in addition, the interaction

between Sb and Nb prevents Sb-Vor Nb-V interactions. VSbO4

and V-Nb-O phases are efficient for propane ammoxidation.

Therefore, this system would not be efficient. On the other

hand, SbCl5 promotes the Sb-V interaction, forming VSbO4 and

segregating niobia as Nb2O5 on calcination. Niobia-promoted

VSbO4 performs better than VSbO4 [52]. The exact nature of

these catalysts if not fully understood, the promotion could be

due to the acidic sites of niobia and to the combination of Vand


Nb into V-Nb-O phases, which are efficient for propane

ammoxidation [52], along with VSbO4. Therefore, it is possible

to prepare Nb-promoted Sb-V-O catalysts in a single step by

appropriate control of the precursors.

SVN1 A, SVN1 B, and SVN2 use niobium oxalates, SVN3

uses Nb2O5 suspension. All the catalysts prepared with SbCl3possess SbNbO4. For a given niobium precursor (oxalate),

SVN1A and SVN1B possess SbNbO4, but SVN2 does not.

The interaction between Sb and V is stronger with SbCl5,

while the interaction between Nb and Sb appears stronger with

SbCl3.

5. Conclusions

Pure VSbO4 phase does not appear to be efficient for

propane ammoxidation to acrylonitrile. It appears that some

segregated Sb oxide is necessary for the catalytic cycle. The

combination of VSbO4 with a-Sb2O4 enhances the selectivity

to acrylonitrile, especially when Sb/V is near 5. The presence of

surface vanadium species cannot be determined in detail, but it

maybe important, since it would be at the surface, which is

directly exposed to the reactants.

For V-Sb-Nb oxide catalysts, the niobium precursor does not

appear to have a critical effect; however, the antimony

precursor shows a trend:

(a) S
bCl3 precursor results in preferential antimony–niobium
interaction; the formation of the SbNbO4 phase is observed

and the catalyst is neither active nor selective to

acrylonitrile formation. Antimony interacts with niobium

at the expense of the VSbO4 and a-Sb2O4active phases.

(b) S
bCl5 precursor favors the redox reaction with vanadium to
form the VSbO4 active phase. Nb improves the catalytic

behavior with respect to the Sb-V-O mixed oxide catalysts.

The presence of Nb-V-O phases could not be detected but its

presence may not be ruled out either.

Acknowledgments

This research was partially funded by the Ministry of

Education and Science, Spain (Project MAT-2002-04000-C02-

01). M.O.G.-P. thanks the Ministry of Science and Technology

of Spain, for a doctorate studies fellowship. M.V.M.-H.

acknowledges the Juan de la Cierva program of the Ministry

of Science and Technology of Spain for financial support. The

authors thank Dr. M.A. Vicente at the University of Salamanca

for his help with the XRD analysis and his helpful discussions.

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ammoxidation of propane over v-sb and v-sb-nb mixed oxides

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