Formation of carboxylic acids from small alkanes in zeolite H-ZSM-5

The activation of propane and isobutane in acidic zeolite H-ZSM-5 in the pr esence of both CO and H2O has been studied by in situ solid-state NMR and G C analysis. Evidence was provided for the conversion of propane to isobutyr ic acid at 373-473K by cleavage of the C-C bond; methane and ethane are als o produced. Isobutane is transformed into pivalic acid with simultaneous pr oduction of hydrogen. The low conversion (1-2%) at this temperature was rat ionalized by the existence of a small number of sites that are capable of g enerating carbenium ions which are trapped by CO at this temperature. A for mate species was observed when CO and H2O were present on H-ZSM-5. This spe cies disappeared in the presence of the alkane. At 573K, the generation of large amounts of CO2 indicates a much higher conversion of the alkanes into carboxylic acids which, however, decompose under the reaction conditions.