Effective NbOx-Modified Ir/SiO2 Catalyst for Selective Gas-Phase Hydrogenation of Crotonaldehyde to Crotyl Alcohol

Abstract

NbOx-modified Ir/SiO2 catalyst (Ir-NbOx/SiO2) showed high activity and selectivity for gas-phase hydrogenation of crotonaldehyde, and Ir-NbOx/SiO2 with Nb/Ir molar ratio of 0.5 (Ir-NbOx/SiO2 (Nb/Ir = 0.5)) provided high crotyl alcohol yield of 87%. This is the highest crotyl alcohol yield among those in gas-phase over reported heterogeneous catalysts. The activities (TOF per surface Ir atom) at low conversion level (40%, W/F = 0.37 gcat·h·mol–1) and high conversion level (97%, W/F = 2.2 gcat·h·mol–1) were calculated to be 0.21 and 0.08 s–1, which are more than 3 times higher than those over reported heterogeneous catalysts. High activity and high yield are derived from the combination of Ir metal with NbOx species. Based on the spectroscopic and kinetic studies, the high activity and high selectivity are attributed to strong adsorption of crotonaldehyde on NbOx species by the high Lewis acidity, and suppression of over-hydrogenation of the produced crotyl alcohol at high conversion level. It is suggested ...