Influence of Ni species on the structural evolution of Cu/SiO2 catalyst for the chemoselective hydrogenation of dimethyl oxalate

A novel family of heterogeneous Cu–Ni/SiO2 catalysts with appropriate metal ratios displayed outstanding selectivity to methyl glycolate (96%) and to ethylene glycol (98%) in the chemoselective gas-phase hydrogenation of dimethyloxalate. The chemical states of nickel species were found to have a strong influence on the structural evolution of the catalysts and correspondent catalytic behaviors. The selectivity to the two products could be tuned by modulating the chemical states of nickel species. It is shown that oxidative nickel species are helpful in improving the dispersion of copper species because of the enrichment of copper on the surface of the nickel species, thus enhancing the catalytic activity and selectivity to ethylene glycol. The selectivity to methyl glycolate could be greatly improved by the Cu–Ni bimetallic catalyst. An 83% yield of methyl glycolate and a 98% yield of ethylene glycol could be obtained over the bimetallic Cu–Ni catalyst and the NiO-modified catalyst, respectively.