Geometric effect in the highly selective hydrogenation of 3-methylcrotonaldehyde over Pt@ZIF-8 core–shell catalysts

Abstract

ZIF-8 encapsulated Pt nanoparticles (NPs) were investigated for the hydrogenation of 3-methylcrotonaldehyde to prenol using the geometric effect. HR-TEM, HAADF-STEM, XRD, nitrogen adsorption isotherm characterization and size-selective reaction evaluation demonstrated that the Pt NPs were encapsulated in the inner space of ZIF-8. The Pt NPs in the Pt@ZIF-8 catalyst were surrounded by apertures with sizes commensurate with 3-methylcrotonaldehyde molecules. These narrow apertures forced the 3-methylcrotonaldehyde molecules to linearly approach the active sites. The CC bond in the middle of the 3-methylcrotonaldehyde molecule was prevented from interacting with the Pt active sites by the narrow apertures around the Pt NPs, while the CO bond at the tail-end was easily adsorbed and further hydrogenated to prenol. Using this geometric effect, the Pt@ZIF-8 catalyst exhibited a high selectivity to prenol (>84%) even at a high conversion (>90%).