GAS-PHASE REACTIONS BETWEEN HYDROCARBONS AND METAL-OXIDES - THE ALO+CH4 REACTION FROM 590 TO 1380 K

A recent ab inito study suggested that gaseous metal oxides can directly abstract H atoms from hydrocarbons, but with considerable barriers. To try to confirm the occurrence of such reactions, the title reaction has been studied in a high-temperature fast-flow reactor. The data are well described by the fitting expression k(590-1380 K) = 9.6 X 10(-39)(T/K)7.96 exp(2468 K/T) cm3 Molecule-1 s-1, with 2sigma precision limits varying with temperature from +/- 4% to +/- 12%. The corresponding 2sigma accuracy limits are about +/- 25%. Comparison of this result to further ab initio and conventional transition-state theory calculations suggests that direct abstraction indeed can occur at the higher temperatures but that one or more other channels, possibly involving AlO insertion into a C-H bond, dominate in the initial attack step. The potential implications of this work for catalytic conversion of methane to higher hydrocarbons are considered.