Chapter 11 - Propylene Epoxidation by O2 + H2 over Au Nanoparticles on Ti-Nanoporous Supports

Abstract

Production of propylene oxide in a single step with no side products has been a long-sought industrial target. While a liquid-phase H2O2/TS-1-based route appears to be imminent, due to handling problems and cost associated with H2O2, researchers have also focused on propylene epoxidation using H2 and O2 over Au/Ti catalysts. Au nanoparticles on mesoporous and nanoporous Ti supports are promising due to their remarkable stability and commercially interesting activity, but significant improvements in H2 efficiency are desired for commercialization. This chapter summarizes the advances in propylene epoxidation using H2 and O2 over Au/TS-1 and Au/Ti-mesoporous supports. Implications of several interesting findings, such as Au particle size and support effects, effect of catalyst pretreatments, effect of gas-phase additives and catalyst promoters, reaction kinetics, and mechanistic insights from quantum chemical calculations, are discussed. A benefit of the catalysts discussed is that many of them delay the propylene oxide (PO) degradation until higher temperatures are reached, thus allowing higher temperatures to enhance PO desorption and avoiding fouling by PO oligomerization. The temperature at which the maximum PO rate occurs is, therefore, a characterization parameter that can be important in the search for higher performance.