Preparation Of Heteroatomic MCM-48 Catalyst And The Research Of Catalytic Performance

The synthesis of dimethyl carbonate by methanol and carbon dioxide is an attracting route, which addresses the goes of carbon dioxide and the problemof methanol overcapacity. Ia3d cubic structure MCM-48 with two independent and inter-connected higher passable channels has a promising prospect in catalysts, but is catalytic inert. The author combined the the advantages of the reaction system and the material, applied the MCM-48 doped with copper or/and nickel as catalysts of the direct synthesis dimethyl carbonate by methanol and carbon dioxide.MCM-48 was synthesized successfully by hydrothermal synthesis in the presence of fluoride ion F- which can enhance hydrothermal stability of mesoporous silica, the effects of template agent, water and the crystallization temperature on molecular sieve structure was scrutinized. The samples were characterized by X-ray diffraction(XRD), Scanning Electron Microscope(SEM), Transmission Electron Microscope(TEM), N2 adsorption-desorption measurements, the results manifested that the optimal synthetic conditions of molecular sieve MCM-48 were as followed:n(Si):n(CTAB)=1:0.20, n(Si):n(H2O)=1:70, T(crystallization temperature)=150 ?.At the optimal synthetic conditions, copper or/and nickel was/were incorporated into/onto MCM-48 by direct hydrothermal synthesis and traditional impregnation, the effects of metal contents, single/double metal, metal molar ratio on molecular sieve structure was scrutinized. The samples were characterized by X-ray diffraction(XRD), Inductively Coupled Plasma Atomic Emission Spectrum (ICP-AES),Infrared Spectroscopy(IR),N2 adsorption-desorption measurements, the results manifested that the MCM-48 retained its orderly three-dimensional structure when doped with certain metal. The most contents of metal can reach n(Si):n(Cu)=1:0.025, n(Si):n(Ni)=1:0.030,n(Si):n(Cu):n(Ni)=1:0.02:0.01 respectively by direct hydrothermal synthesis, the mass fraction of copper oxide and nickel oxide can reach 12%by traditional impregnation.The CO2 adsorption capacity of samples by direct hydrothermal synthesis was measured by Cahn-2000 high vacuum electronic balance testing system, the results manifested that the CO2 adsorption capacity increased with the adding of metal contents at the beginning and then decreased with the adding of metal contents when doped with single metal, and the CO2 adsorption capacity was highest when n(Si):n(Cu)=0.015 and n(Si):n(Ni)=0.015 respectively. The CO2 adsorption capacity decreased with the adding of metal contents when doped with double metals and n(Cu):n(Ni)=2:1. The variation tendency of CO2 adsorption capacity when doped with equivalent metal amount and different molar ratio was as followed:Vab(doped with double metals and n(Cu):n(Ni)=2:1)> Vab(doped with single metal Cu)> Vab(doped with single metal Ni)> Vab(doped with double metals and n(Cu):n(Ni)=0.5 or 1).The catalytic performance of samples was scrutinized at the condition of 150 ?,10 mL methano1,7.5 bar CO2,9 h and the reaction conditions were optimized, the results manifested that Cu-Ni-MCM-48-0.010-0.005 showed the best performance, the optimal reaction temperature was 160 ? and the optimal reaction pressure was 10 bar among the range of investigated.