Hydrogenation of Dimethyl Malonate to 1,3-Propanediol Catalyzed by Cu/SiO2 Catalyst: Reaction Network and Effect of Cu+/ Cu0 on Selectivity
1,3-propanediol, a vital monomer for the manufacture of commodity poly trimethylene-terephthalate, is commercially produced nowadays through either hydration of acrolein or hydroformylation of ethylene oxide. Herein, for the first time, we present the investigation of an alternative route for 1,3-propanediol production from vapor-phase catalytic hydrogenation of syngas-derived dimethyl malonate on Cu/SiO2 catalyst. The catalytic reaction network has been disclosed for Cu/SiO2 catalyst, the reaction proceeds through sequential hydrogenation with methyl 3-hydroxypropionate as the primary product, which can be further converted into 1,3-propanediol or methyl propionate. Excessive hydrogenation of 1,3-propanediol or methyl propionate leads to the formation of n-propanol. Meanwhile, a small amount of dimethyl malonate cracks into methyl acetate. The structural and textural properties of Cu/SiO2 catalysts with varied copper loadings were extensively characterized by X-ray diffraction, Fourier transform infrared spectroscopy, H2-temperature programmed reduction, X-ray photoelectron spectroscopy, N2 physisoprtion, CO chemisorption, N2O titration, and transmission electron microscopy. A correlation of areal activity to copper components suggests that metallic copper modified by the co-present Cu+ specie may be the active site for the hydrogenation. The highest 1,3-propanediol selectivity was achieved on a catalyst with maxima Cu+/(Cu0+Cu+) ratio of 0.41. The revelation of catalytic network and insight into the active species can provide guidance for future rational design of catalysts for regioselevtive hydrogenation of C=O bonds in dimethyl malonate.