Oxidative conversion of C1-C3 alkanes by vanadium oxide catalysts. DFT results and their accuracy

Elementary steps in the oxidative conversion of methane, ethane, and propane by supported vanadium oxide species are studied by density functional theory, specifically B3LYP. Two models are adopted, namely O = V(OH)(3) and O = VSi7O12H7, which yield similar energy profiles. The initial and rate-determining step is hydrogen abstraction. Within the C1-C3 series, energy barriers and reaction energies follow the same trend as the C-H bond strength in the different alkanes. For methane, only methanol formation is possible whereas for ethane and propane, oxidative dehydrogenation yields the corresponding alkenes. Single point CCSD(T)/TZVP calculations are used to assess the B3LYP error. For the barrier of the initial hydrogen abstraction the B3LYP error is larger than usual, -40 to -60 kJ/mol. With the nonhybrid BP86 and PBE functionals even larger errors occur and the potential energy surface is qualitatively different. (c) 2008 Wiley Periodicals, Inc.