In Situ Formed Fe Cation Modified Ir/MgO Catalyst for Selective Hydrogenation of Unsaturated Carbonyl Compounds

Selective hydrogenation of alpha,beta-unsaturated ketones to alpha,beta-unsaturated secondary alcohols is a challenging reaction for heterogeneous catalysts because of the nonuniformity of their surface active sites, and high-yield synthesis of the target alpha,beta-unsaturated secondary alcohols has not been achieved by heterogeneous catalysts. Herein, we found that Fe cation modified Ir/MgO acted as an effective heterogeneous catalyst for the reaction, providing high yield (up to 90%) of alpha,beta-unsaturated secondary alcohols. The activity is high (initial TOF = 12 min(-1) and TOFS (TOF per surface Ir site) = 84 min(-1)), and the TOF is more than 10 times higher than those of the reported heterogeneous catalysts. To the best of our knowledge, the TOFS is the highest among the reported homogeneous and heterogeneous catalysts under additional base-free conditions. The catalyst was easily fabricated by only mixing Ir/MgO and Fe cation precursor in the reaction media, and the active sites were proposed to be the interface among Ir metal, Ir4+, and Fe2+ species over MgO support based on kinetic studies and catalyst characterizations such as XPS, TPR, XRD, TEM, and ICP. The cation anion pair sites of Fe2+ and O2- formed at the active sites will bring about formation of active hydrogen species (H- and H+), leading to high selectivity and activity. The catalyst was also applicable to selective hydrogenation of alpha,beta-unsaturated aldehydes, providing the corresponding alpha,beta-unsaturated primary alcohols quantitatively (yield >99%).