Promoting effect of Ir on the catalytic property of Ru/ZnO catalysts for selective hydrogenation of crotonaldehyde

•The addition of Ir in Ru/ZnO effectively enhances the catalyst stability.•The enhanced stability is due to RuIr alloy and weakened surface acidity.•Catalyst deactivation is due to deposition of organic compounds on the surface.•Strong CO chemisorption on metal surface also accounts for catalyst deactivation.