NbO x -modified Ir/SiO 2 catalyst (Ir-NbO x /SiO 2 ) showed high activity and selectivity for gas-phase hydrogenation of crotonaldehyde, and Ir-NbO x /SiO 2 with Nb/Ir molar ratio of 0.5 (Ir-NbO x /SiO 2 (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 g cat •h•mol −1 ) and high conversion level (97%, W/F = 2.2 g cat •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 NbO x species. Based on the spectroscopic and kinetic studies, the high activity and high selectivity are attributed to strong adsorption of crotonaldehyde on NbO x species by the high Lewis acidity, and suppression of over-hydrogenation of the produced crotyl alcohol at high conversion level. It is suggested that the formation of hydride species at the interface between Ir metal and NbO x species can promote the selective hydrogenation considering the reaction order with respect to hydrogen pressure. High yield and high activity of Ir-NbO x /SiO 2 can contribute to energy saving, cost reduction, and waste reduction, which are directly connected to realization of sustainability.