Mechanistic insights on the promoting roles of IrFe alloy in selective hydrogenation of crotonaldehyde

Schematic diagram of the differences in crotonaldehyde adsorption/hydrogenation on Ir NPs and IrFe alloy and thus the catalytic performance. [Display omitted] •IrFe alloy was more active and selective than Ir NPs in the hydrogenation of crotonaldehyde.•Catalytic performance of the IrFe alloy was related to its electronic structure.•Ir-Fe pair provided adsorption site for C = O group in crotonaldehyde.•Adsorption of crotonaldehyde was much enhanced on IrFe alloy and thus improved activity.•Hydrogenation of C = O bond was easier on IrFe alloy and thus improved selectivity. IrFe alloy nanoparticles with different Ir/Fe molar ratios were synthesized and exhibited good performance in the gas phase selective hydrogenation of crotonaldehyde (CRAL). The IrFe alloy with an Ir/Fe ratio of 19/1 gave a turnover frequency (TOF) of 0.022 s−1 at 80 °C and a crotyl alcohol (CROL) selectivity of 91 %, while the bare Ir/BN catalyst gave a TOF of 0.0014 s−1 and a CROL selectivity of 74 %. Detailed characterizations, kinetic investigation, and in situ spectroscopic study revealed that the altered electronic structure of the IrFe alloy with transfer from Fe to Ir species was essential for its improved performance. Also, density functional theory calculations indicated that such an electronic structure resulted in strong CRAL interaction with the Ir-Fe entity, thus higher adsorption capacity and lower reaction barrier than that on the Ir-Ir counterpart, which accounted for the higher activity. Moreover, the hydrogenation of C = O bond required lower barrier on the Ir-Fe site than that on the Ir-Ir, which well explained the higher selectivity to CROL.