Hydrocarbon formation upon gamma radiolysis of H 2CO mixtures in the presence of activated alumina surfaces

Abstract

The formation of hydrocarbon products in the gamma radiolysis of a 3:1 hydrogen-carbon monoxide mixture in the presence of a gamma alumina catalyst has been investigated at 250 torr (33.32 kPa) pressure over a temperature range of 196–363 K where no thermally initiated reaction was detected. The yields of all products were substantially increased over those in homogeneous radiolysis with alkane yields being increased about one order of magnitude while alkene yields increased 3–4 orders of magnitude. Yields for both alkane and alkene production decreased with increasing carbon number. The predominant products were carbon dioxide, ethylene, and propylene with G-values of 59, 11, and 3.8 at room temperature. Smaller yields ( G<1) of butenes, pentenes, ethane, propane, butanes, and pentanes were found. As temperature was increased, yields of all hydrocarbon products increased, while the carbon dioxide yield diminished. The results suggest formation of higher hydrocarbon products via a stepwise mechanism with an incremental energy requirement for each additional CH 2 group. The mechanism may involve the formation of formate structures on the alumina surfaces; carbon monoxide disproportionation to CO 2 and C is not believed to be involved.