Density Functional Theory Calculations of the Oxidative Dehydrogenation of Propane on the (010) Surface of V₂O₅^†

Abstract

Density functional theory and the calculations of oxygen nucleophilicity have been applied to an analysis of the oxidative dehydrogenation (ODH) of propane on the (010) surface of V 2 O 5 . These calculations show that the energetically preferred initial step is the dissociative adsorption of propane to form i-propoxide and hydroxyl species. Two VdO groups [O(1)] bonded by a V-O-V bridge are required. One of the vanadyl groups attacks the -C atom of propane and is converted to a V-OCH 2 (CH 3 ) 2 species, whereas the other vanadyl group is converted into a V-OH group. The activation barrier for this process is 9.4 kcal/mol. Dissociative adsorption to form an n-propoxide can also occur, but the activation barrier for this process is 14.5 kcal/mol. Propene and water are formed via a concerted process in which an H atom of one of the methyl groups of i-propoxide reacts with an O(3)H group. Exploration of alternative pathways for this step reveals that neither O(1, 2, 3), O(1)H, nor O(2)H are sufficiently reactive. These findings are in good qualitative agreement with experimental observations concerning the mechanism and kinetics of propane ODH.

Oxidative dehydrogenation of propane over low-loaded vanadia catalysts: Impact of the support material on kinetics and selectivity

“…On the basis of DFT calculations, Rozanska et al [26] find the vanadyl oxygen to be responsible for the selective dehydrogenation of propane over silica supported vanadia catalysts. Although similar calculations have not been done so far for other support materials, a study of Bell et al [27] for unsupported V 2 O 5 also assign the V=O as the crucial active site for the first C-H bond abstraction as the rate determining, though the second hydrogen abstraction may involve a V-O-V bond. In order to obtain additional information to enable discrimination between these models, we determined the dependence of ODP TOFs and activation energies on the EN of the cation of the respective support material.…”

“…For V-O-support bonds being the active site, the calculations revealed much higher activation energies (~ 200 kJ mol -1 ) [26]. For an unsupported V 2 O 5 cluster a value of about 160 kJ mol -1 was calculated [27].…”

“…For silica supported vanadia catalysts calculations considered monomeric and dimeric vanadium oxide surface species to take part in ODP [26]. It is suggested that for a model (010) surface of V 2 O 5 system at least two V=O goups bonded by a V-O-V bond are required for the dissociative adsorption of propane [27].…”

Potential of High-Frequency EPR for Investigation of Supported Vanadium Oxide Catalysts

“…Many experimental and theoretical approaches to this subject have been performed in the past decades. [1][2][3][4][5][6] However, the key factors for control of the catalytic performance of this reaction are still not fully understood. Supported vanadia catalysts offer a high catalytic activity, but in the case of ODP the similarity of reactants and products leads to poor selectivity.…”

Transient kinetics of toluene interaction with V/Ti-oxides in anaerobic conditions

“…The concentration of benzyl, benzyloxide species and hydroxyl groups should be negligible in the studied conditions in accordance with the transient response data. The necessity of two oxygen sites in the first step of alkanes interaction with V 2 O 5 was shown by the density functional theory calculations [26,27]. In the Step (2), BA reacts with the YO site with the benzoate (YC 6 H 5 COO) formation.…”