Hydrogenation of crotonaldehyde over ligand-capped Ir catalysts: Metal-organic interface boosts both activity and selectivity

ABSTRACT Ir nanoparticles (NPs) were synthesized via a colloidal method using tetradecyltrimethyl ammonium bromide (TTAB) as the ligand, and the supported Ir/BN catalysts were employed for selective hydrogenation of crotonaldehyde (CRAL). It was found that by proper thermal treatments, the TTAB-capped Ir NPs were very active and selective for the reaction. The Ir/BN catalyst calcined at 300 °C with surface TTAB residue gave a quasi-steady state turnover frequency (TOF) for crotyl alcohol (CROL) formation of 0.02 s −1 and a CROL selectivity of 94.4%, while that calcined at 500 °C with clean surface gave a TOF of 0.004 s −1 and a CROL selectivity of 56.2%. The Ir-TTAB interface was essential for the enhanced performance. In-situ IR spectra along with kinetic investigation revealed that TTAB improved CRAL adsorption and strengthened C=O adsorption, which accounted for high activity and selectivity. However, high coverage of TTAB on the Ir surface suppressed the H 2 adsorption and consequently lowered the activity. Thus the findings provided useful information on the design of efficient catalysts for selective hydrogenation.