Infrared studies of propene and propene oxide adsorption on nanoparticulate Au/TiO₂

Direct gas-phase epoxidation of propene to propene oxide over a heterogeneous catalyst holds the potential to revolutionize production of one of the world's major commodity chemicals. New research into fundamental aspects of propene chemistry on nanoparticulate catalysts will help guide strategies for materials development. In the current study, Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) have been employed to explore the molecular-level details of propene and propene oxide binding at a Au/TiO₂ catalyst. Competitive binding studies for propene and carbon monoxide reveal that propene readily displaces CO from: first, interfacial Au ||TiO₂ sites, then low coordinated Au sites at particulate corners and edges, and finally terrace regions of the particles. DFT calculations show that the [Formula presented] bond of propene weakens upon coordination to Au, which suggests that these sites may activate the molecule for epoxidation. Like propene, propene oxide adsorbs on both Au sites and Ti sites. In addition, Ti-OH sites also readily bind the oxide. However, competitive binding experiments show that the propene oxide adsorption is favored relative to propene on all sites, which would likely passivate the catalyst at room temperature.