Towards selective catalytic oxidations using in situ generated H2O2

Abstract

A series of Ti-modified mesoporous SiO2 materials (SBA-15 and MCF) are prepared, characterised and used as catalysts in the selective epoxidation of a probe alkene (cyclohexene) using H2O2 as an oxidising agent. Similarly, a series of mesoporous SiO2-supported monometallic and bimetallic DMAP-stabilised Au and Pd nanoparticles were prepared, characterised and used as catalysts in the production of H2O2 from dilute H2(g)+O2(g) mixtures.The metallic nanoparticles were then supported on the Ti-modified mesoporous SiO2 and these hybrid materials were characterised and their activities in the selective epoxidation of alkenes in the presence of H2(g)+O2(g) mixtures (where H2O2 would be formed in situ) were studied. The bimetallic Au/Pd nanoparticles (which were most active in the production of H2O2 from H2 and O2) were not the most active or selective in the combined reaction. This was ascribed to the Pd component of the nanoparticles promoting hydrogenation of the probe alkene more rapidly than the formation of H2O2. The selectivity of Au nanoparticles in the presence of H2(g)+O2(g) was higher than that of the same catalysts in the presence of H2O2(aq).