Theoretical and Experimental Study of Light Hydrocarbon Ammoxidation and Oxidative Dehydrogenation on (110)-VSbO₄ Surfaces

Abstract

Density Functional Theory (DFT) calculations have been performed for ethane, ethylene, propane, and propylene adsorption on the rutile VSbO4 structure to uncover the reaction mechanism during both ODH and ammoxidation reactions. This study is complementary to a previous paper in which the adsorption of ammonia on this structure was deeply analyzed, and in addition, experimental activity results for both reactions are shown to complete the theoretical DFT calculations. These results show that ammonia, ethane, and ethylene compete for the same active sites, the former adsorbing strongly. This explains why this catalytic system is not active for ethane ammoxidation; the presence of ammonia blocks the other molecule adsorption sites and prevents ethane oxidative dehydrogenation to ethylene. Such competition does not occur with propane or propene since the adsorption of both ammonia and hydrocarbon is possible at different sites, explaining why this catalytic system is active for propane ODH reaction. During ammoxidation, molecularly dispersed VOx species are able to transform the propane molecule into propylene. Then, intermediate propylene can coadsorb along with ammonia on the trirutile VSbO4, inserting the nitrogen atom that forms acrylonitrile. Calculations show that the adsorptions studied are more favored when the rutile structure presents a cationic vacancy.

Investigations on the Antimony Promotional Effect on CeO2–WO3/TiO2 for Selective Catalytic Reduction of NOx with NH3

“…[29][30][31] It has been demonstrated that antimony-doped catalysts are active and selective for several partial oxidation processes. [32] For example, doping SnO 2 oxide with Sb 3 + decreased the conductivity, whereas doping with SbV enhanced the n-type conductivity. [33,34] However, investigations of antimony-doped de-NO x catalysts are rare and the promotional effect of the antimony on the de-NO x catalysts is still unclear.…”

Propylene Adsorption On a Nonstoichiometric VSbO4(110) Surface

“…43 Metal-cation defects also facilitates the formation of redox couples V 4+ /V 3+ , enhancing the catalytic activity of antimonate in hydrocarbon selective oxidation reactions. 31 41 In our calculations, we have selected the (110) plane because it appears to be one of the most stable crystal face of rutile oxides, 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 7 The atom projected density of states (PDOS) was calculated by projecting one-electron states onto spherical harmonic atomic orbitals centered on atomic sites. A qualitative study of the bonding between different atoms was also performed using the Overlap Population (OP) concept, 47 as implemented in the SIESTA code.…”

“…[27][28][29][30][31] In addition, the adsorption of NH 3 on this solid has been analyzed. 32,33 On the other hand, there are no extensive DFT studies about propylene adsorption on a cation-deficient VSbO 4 (110) surface.…”

“…While configurations 5 and 6correspond to a parallel approach to the surface via the double bond C 2 =C 3 , to V and Sb atoms, respectively. A study using similar approaches was performed by Rojas et al31 …”

Chapter 2. Theoretical studies of selective propane oxidation and ammoxidation over vanadium-based multi-metal oxides

“…56,57 It was demonstrated that the lowering of vanadium concentration in this mixed oxide lattice was important for improving its selectivity towards propene. 58 Rojas et al 59,60 recently conducted DFT and experimental study of light hydrocarbon (ethane, ethylene, propane, and propylene) ammoxidation and on VSbO 4 . Their theoretical study of this catalytic system was based on the bulk (110) surface of VSbO 4 .…”