Enhanced productivity toward propene oxide in the direct propene epoxidation with hydrogen and oxygen over gold nanoparticles supported on titanium‐grafted silica was achieved by adjusting the gold–titanium synergy. Highly isolated titanium sites were obtained by lowering the titanium loading grafted on silica. The tetrahedrally coordinated titanium sites were found to be favorable for attaining small gold nanoparticles and thus a high dispersion of gold. The improved productivity of propene oxide can be attributed to the increased amount of the interfacial AuTi sites. The active hydroperoxy intermediate is competitively consumed by epoxidation and hydrogenation at the AuTi interface. A higher propene concentration is favorable for a lower water formation rate and a higher formation rate of propene oxide. Propene hydrogenation, if occurring, can be switched off by a small amount of carbon monoxide.

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A study on the gas-phase epoxidation of propene with vapor hydrogen peroxide has been carried out. The main purpose was to understand the key factors in the reaction and the relationship between epoxidation of propene and decomposition of hydrogen peroxide, which is the main side reaction. The decomposition was highly influenced by the materials used, being higher in metals than in polytetrafluoroethylene (PTFE) and glass, and it was complete when the epoxidation catalyst, TS-1, was introduced in the system. However, when propene was added, the peroxide was preferentially used for the epoxidation, even with amounts of catalyst as small as 10 mg, reaching productivities of 10.5 kgPO·kgcat –1·h–1 for a gas hourly space velocity (GHSV) of 450 000 mL·gcat –1·h–1. The hydrogen peroxide was converted completely in all the experiments conducted, with a selectivity to PO of around 40% for all peroxide concentrations. Finally, if concentrations of propene higher than the stoichiometrically required amounts were used, the selectivity to PO increased to almost 90%.

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Gold nanoparticles supported on a MgCuCr2O4 spinel catalyze the aerobic oxidation of propylene to acrolein. At 200 °C, the selectivity is 83% at a propylene conversion of 1.6%. At temperatures above 220 °C, propylene combustion dominates. The good performance of Au/MgCuCr2O4 in selective propylene oxidation is due to the synergy between metallic Au and surface Cu+ sites. Kinetic experiments (H2 addition, N2O replacing O2) show that the reaction involves molecular oxygen. DFT calculations help to identify the reaction mechanism that leads to acrolein. Propylene adsorbs on a single Au atom. The adsorption of propylene via its π-bond on gold is very strong and can lead to the dissociation of the involved Au atom from the initial Au cluster. This is, however, not essential to the reaction mechanism. The oxidation of propylene to acrolein involves the oxidation of an allylic C–H bond in adsorbed propylene by adsorbed O2. It results in OOH formation. The resulting CH2–CH–CH2 intermediate coordinates to the Au atom and a support O atom. A second C–H oxidation step by a surface O atom yields adsorbed acrolein and an OH group. The hydrogen atom of the OH group recombines with OOH to form water and a lattice O atom. The desorption of acrolein is the most difficult step in the reaction mechanism. It results in a surface oxygen vacancy in which O2 can adsorb. The role of Cu in the support surface is to lower the desorption energy of acrolein.