High-performance Pt/CeO2-ZrO2 catalysts for selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols under mild reaction conditions: “Giant” hydrogen spillover behind the activity enhancement

Abstract

Pt supported on CeO2-ZrO2 mixed oxide showed unusually high activity and regioselectivity compared to common commercial hydrogenation catalysts in hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols. DRIFTS-CO, TEM, XPS, TPR-H2 studies demonstrated that the CeO2-ZrO2 support stabilizes Pt as small clusters, especially for the catalysts with ultra-low Pt loadings < 0.1 % wt. Interaction of Pt clusters with the easily reducible CeO2-ZrO2 mixed oxide leads to intense low-temperature hydrogen spillover effect, which in turn is responsible for active hydrogen species generation on Pt and their transfer to the support leading to reduction of CeO2 with the formation of Ce3+, where the carbonyl bond can be adsorbed and activated. According to the results of EPR studies of hydrogen species generated on the catalyst surface, we assume that hydrogen on a Pt/CeO2-ZrO2 catalyst can undergo heterolytic dissociation with the formation of hydride ions, which provide selective carbonyl bond hydrogenation, but not with the predominant formation of radical type (H●) species that lead to unselective hydrogenation of both C = O and C = C bonds. A careful 1H magic angle spinning solid-state NMR (1H MAS SS NMR) study of hydrogen adsorbed on Pt/CeO2-ZrO2 and Pt supported on non-reducible oxide (SiO2) confirmed the formation of hydride on Pt/CeO2-ZrO2, whilst only molecular hydrogen was detected on the Pt/SiO2 sample.