Selective hydrogenation of crotonaldehyde over Ir/BN catalysts: kinetic investigation and Ir particle size effect

A series of Ir/BN catalysts with same Ir contents (2 wt%) were calcined at different temperatures and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the thermal treatment exerted significant impacts on the structural and electronic properties of the 2Ir/BN catalysts. The catalyst calcined at 500 °C (2Ir/BN-5) showed the best performance, with a steady state of conversion of ca. 21% and a crotyl alcohol selectivity of ca. 83% at reaction temperature of 80 °C. Kinetic analysis indicated that the enhanced activity on the 2Ir/BN-5 catalyst was related to its higher surface coverage of crotonaldehyde because of the presence of small Ir particles (with a mean diameter of 3.4 nm) compared to those in the catalyst calcined at 600 °C (2Ir/BN-6, with a mean diameter of 4.4 nm). Also, the surface of the Ir species in the 2Ir/BN-5 catalyst are more electron-enriched compared to that in the 2Ir/BN-6, which suppressed the adsorption of C=C bond and thus improves the selectivity to CROL.