Effect of surface hydroxyl groups on the reactions of i-propyl radicals adsorbed on silica at 77 K

Abstract

The reaction of propylene adsorbed on silica gel with gaseous hydrogen atoms has been studied. Product selectivity [C₃H₈]/[C₆H₁₄], is a function of surface coverage, hydrogen atom concentration and out-gassing temperatures. Selectivity decreases as out-gassing temperatures are increased. This is interpreted in terms of increased surface diffusion due to decreased radical hydroxyl interactions. Exposure to saturated water vapour shows that surface dehydration is irreversible at high out-gassing temperatures. When propylene is diluted with ethane or propane to monolayer coverage product selectivity increases. The order of effectiveness in limiting surface diffusion is C₃H₈ > C₂H₆.