Effect of reduction temperature on selective hydrogenation of crotonaldehyde over Ir/TiO2 catalysts

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 °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 CC 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 °C was appropriate for high activity and selectivity, due to the moderate interaction between the CO bond and the Ir species, as well as the weakened surface Lewis acid sites. However, higher reduction temperature (500 °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).

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► The charge-deficient Ir species reduced at 100 °C favor CC bond hydrogenation.
► Strong Lewis acid sites are detrimental to catalytic behaviors.
► Ir/TiO2 catalysts reduced at 300 °C have the highest activity and selectivity.
► Moderate electron density and Lewis acidity are the virtues for high selectivity.
► The charge-rich Ir species reduced at 500 °C suppress activity and selectivity.