| CO2is the main gas causing the greenhouse effect and is also a kind of potential carbon resources.If CO2is synthesized the dimethyl carbonate(DMC) which is a chemical raw material,it can solve the problem of CO2going and effective utilization.At present,the direct synthesis of DMC from CO2and CH3OH has been paid more attention, but CO2conversion radio is lower.Therefore,the main problem which needs to be settled is looking for the high efficiency catalyst and good technology system.MCM-48mesoporous molecular sieve has a two independent of each other three-dimensional channel structure,so it is favorable for the diffusion of molecular and has advantages in field of macromolecular catalysis. However, MCM-48has few catalytic active sites and lower hydrothermal stability,so it can’t be directly used in catalytic reaction.In this paper,the excellent catalyst is synthesized,namely,Cu or Ni is doped into MCM-48with better hydrothermal stability;The catalytic performance is analyzed by the method of the system pressure variation,and the reaction process system is done some exploring research.In this paper,MCM-48was synthesized by the directly hydrothermal method under the condition of fluorine ion,then,the copper or/and nickel was/were doped in MCM-48.And the structural performance of these samples was characterized by XRD、SEM、ICP-AES、FTIR、 Py-IR、TEM and so on.The results showed that (1)when n(KF)/n(Si)=0.10,the structural performance of MCM-48was the best,and it had uniform size and spherical particles,besides,that F-could make MCM-48skeleton more perfect could improve hydrothermal stability of MCM-48;(2)when the molar ration of n(M)/n(Si)(M=Cu or Ni) was in0-0.03, MCM-48doped cu or ni could be prepared,which had the cubic structure of MCM-48(Ia3d) and had the higher content of copper and Nicker.These reuslts indicated that when copper or nicker could replace part of the silicion, MCM-48containing active center also could be synthesized.Besides,when n(Cu)/n(Si)=0.015, structural performance of the sample was considered the best.But MCM-48doped nickel didn’t have the optimal value.At the same time,when n(Cu+Ni)/n(Si)=0.01-0.02, MCM-48doped Cu and Ni had also been synthesised.(3) The cubic structure of Cu-MCM-48could be effected by F-and the molar ratio of n(CTAB)/n(Si),however,copper salts with different anions almost had no effect on Cu-MCM-48. MCM-48/ZSM-5mesoporous/microporous composite molecular,whose cell wall had MFI structure, was synthesized by the two-crystallization method,and the structural performance of the samples was characterized by XRD、SEM、Py-IR、TEM.The results showed that (1) when n(NaOH)/n(Si)=0.3,the reaction time t=4h and the mole ratio of n(Na2SO4/n(Si) was0.005-0.015in the first step crystallization process, the excellent structural performance of MCM-48/ZSM-5composite molecular could be synthesized,and the sample had uniform size and spherical particles.Besides,SO42-can promote the growth of microporous structure;(2)On the basis of the above conditions,when n(M2+)/n(Si)=0.005-0.015, Cu(Ni)-MCM-48/ZSM-5could be synthesized successfully,and when n(M2+)/n(Si)=0.01, Cu(Ni)-ZM-3-0.01had the excellent structure performance.(3)Other acid radical ions such as Cl-、NO3-、CH3COO-also could contribute to the formation of microporous structure.By using the method of the system pressure change,under the proper reaction condition (temperature120℃, CO2pressure6.5bar and reaction time13h),according to the pressure variation trend,the catalyst Cu-Ni-MCM-48-0.010-0.005had better effect. Besides, the catalyst Cu-Ni-MCM-48-0.010-0.005(n(Cu2+)/n(Si)=0.010, n(Ni2+)/n(Si)=0.005) which had been responsed also remained good mesoporous structure of MCM-48. The reactor with removing the water and increasing the disturbance was designed.These improvements could effectively increase the disturbance of reactants,strengthen mass transfer and make the contact of the reactants better.Besides, water could be removed timely,it could promote the reaction to the positive direction. |
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