Mono-atomically dispersed Pd on TiO2 as a catalyst for epoxidation of light olefins at low temperatures in the presence of H2 and O2

Palladium supported at extremely low loading on TiO2 catalyzed epoxidation of light olefins (except ethylene) in the presence of O2 and H2 at ambient temperature. Propylene oxide (PO) was obtained from propylene (1–2% yield; 30–60% selectivity) together with propane. Simple oxidation of H2 to water was slow, and the ratio of H2 used for PO formation in the reacted H2 was 10–25%. A Pd concentration of 0.005–0.01 atom-Pd/nm2–TiO2 was optimum for epoxidation, and the major product at 0.02 atom-Pd/nm2 was acetone. That the distributions for a Pd/TiO2 catalysts prepared from Pd nitrate and from a Pd-tetraphenylporphyrin complex at the same Pd loading were similar suggests that Pd was supported mono-atomically on TiO2. We propose that PO formed via reaction between propylene adsorbed on Pd and an active species derived from reaction of H2 and O2 on TiO2 (perhaps ·OOH).

Research highlights
► We prepared TiO2 catalyst on which Pd is mono-atomically well dispersed.
► This catalyst is effective for epoxidation of lower olefins at ambient temperature.
► Pd is zero valent and epoxidation requires the presence of H2 and O2.