Effects of water vapor on the radiolysis of methane over molecular sieve 5A

Effects of the addition of H2O on the radiation-induced chemical reaction of methane over molecular sieve 5A at 4600C have been studied by product analysis. Hydrogen, carbon monoxide, carbon dioxide and hydrocarbons consisting mainly of C2 and C3 alkanes and alkenes were produced from CH4 + H2O mixtures at high conversion levels. The yields of hydrocarbons from 3:1 and 3:2 CH4 + H2O mixtures decreased slightly with time but those from 3:4 mixture showed no decrease with time. When the molecular sieve 5A that had been irradiated in flowing methane was reirradiated in the presence of H2O, carbonaceous solid produced from methane on molecular sieve 5A was readily decomposed to carbon dioxide, carbon monoxide, hydrogen and hydrocarbons, mainly alkanes. Therefore, it is concluded that the suppression of decrease of product yields with time by the addition of H2O is mainly ascribed to decomposition of the carbonaceous solid by H2O under electron beam irradiation. The role of added H2O is also discussed in connection with the conventional methane-steam reforming reaction. (author)