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

Selective hydrogenation of α,β-unsaturated ketones to α,β-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 α,β-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 α,β-unsaturated secondary alcohols. The activity is high (initial TOF = 12 min^-1 and TOF_s (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 TOF_s 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 O^2- 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 α,β-unsaturated aldehydes, providing the corresponding α,β-unsaturated primary alcohols quantitatively (yield >99%).