Vapor-phase selective hydrogenation of crotonaldehyde was conducted over Ir/TiO2 catalysts to investigate the effect of reduction temperature on the catalytic behaviors. The catalyst reduced at 100 degrees C contained large amount of strong Lewis acid sites, which was detrimental to the activity because of the strong adsorption of crotonaldehyde molecules on the active sites. Also, the selectivity to crotyl alcohol was suppressed due to the interaction between C=C bond and the charge-deficient Ir species, which favored the formation of butanal. When the catalyst was reduced at high temperature, it was found that 300 degrees C was appropriate for high activity and selectivity, due to the moderate interaction between the C=O bond and the Ir species, as well as the weakened surface Lewis acid sites. However, higher reduction temperature (500 degrees C) led to a strong bonding of carbonyl carbon and the charge-rich Ir species and suppresses the activity, which may be related to a strong metal-support interaction (SMSI). (C) 2012 Elsevier B.V. All rights reserved.