Deep UV photocatlytic activation of ethane on silica surfaces

Abstract

Deep UV photolysis (165 or 185 nm) of surface silanol groups leads to the homolytic Osingle bondH bond breaking, generating silyloxyl radicals and hydrogen atoms. Silyloxyl radicals are able to activate ethane through hydrogen abstraction, whereby ethyl radicals are formed. Coupling of these ethyl radicals with silyloxyl radicals forms surface bound ethoxysilane that eventually will form ethanol. The product distribution of this radical process depends on the absence or presence of oxygen and may lead to the formation of ethanol together with light alkanes (methane, propane, butane and hexane) accompanied by C2 (acetaldehyde and acetic acid) and C1 (methanol, formaldehyde and formic acid) oxygenates. The presence of oxygen enhances ethane conversion and quenches the formation of alkanes by trapping alkyl radicals. It was found that micro and mesoporous silicas behave qualitatively similar with some differences in the product distribution. The most efficient material (higher conversion and higher percentage of products in the solid) was found to be Al-MCM 41. The energy consumption estimated based on a conversion of 6% on commercial beta zeolite was 2.0 Gcal per mol of ethane converted that is about 3.6 times smaller than the energy consumed form methane activation through an analogous process.