Photocatalytic Reaction for Synthesis of Dimethyl Carbonate from CO_2 and CH_3OH over Cu/NiO-MoO_3/SiO_2 Catalyst

The Cu/NiO-MoO_3/SiO_2 catalyst was made by the methods of surface reaction modification and isometric impregnation.The structure,chemisorption and photoabsorption properties of Cu/NiO-MoO_3/SiO_2 were studied by XRD,Raman,IR,TPD and UV-Vis DRS techniques,and the reaction behavior for the photocatalytic reaction of CO_2 and CH_3OH to dimethyl carbonate(DMC) was studied by photo-stimulated reaction technique.The results showed that the addition of Cu and NiO greatly increased the dispersion of MoO_3 on SiO_2,and Cu and NiO could also disperse evenly on the support.The CO_2 horizontal state with high activity and the CH_3OH molecular and dissociative adsorption states formed on the surface of Cu/NiO-MoO_3/SiO_2 catalyst under the synergic action of metallic Cu sites and Lewis acid sites(Mo~(6+) or Ni~(2+)).The(Mo-O-Ni) bonds formed and the absorption intensity was enhanced through the coupling of MoO_3 and NiO.The absorption region was expanded to visible light after Cu was supported on the coupled semiconductor NiO-MoO_3/SiO_2.Compared with the thermal surface catalytic reaction,the photo-stimulated surface reaction for synthesis of DMC from CO_2 and CH_3OH over Cu/NiO-MoO_3/SiO_2 could proceed at lower reaction temperature and give higher reactant conversion.Under the proper conditions,the CH_3OH conversion was up to 13.9% with DMC selectivity of 90.1%.