Preparation Of Carbon Supported Copper Catalyst And Its Performance For Synthesis Of Dimethyl Carbonate

Dimethyl carbonate（DMC）is an important intermediate in organic synthesis,due primarily to a variety of reaction properties caused by the structure of carbonyl,methyl and methoxy groups.Oxidative carbonylation of methanol to DMC has important research value and wide application prospect in alleviating the current overproduction of methanol and developing new coal chemical industry owing to its abundant raw materials,high atomic economy,mild reaction conditions and no harmful by-products.For this reaction,carbon supported copper catalysts have attracted much attention due to their various supports and excellent catalytic performance.In the previous work,the copper-based catalysts with different supports,including activated carbon,carbon aerogels,graphene,hollow carbon spheres and carbon nanotubes,showed a significant size effect in the oxidative carbonylation of methanol,that was,the smaller the grain size of the copper nanoparticles,the higher the activity of the reaction.Therefore,how to effectively improve the dispersion of copper species and accurately control the grain size of copper is crucial for enhancing the catalytic performance of the methanol oxidative carbonylation reaction,and it is also the current research focus in this field.Based on the above,the excellent support with high specific surface area and novel preparation method were studied respectively and two series of catalysts were designed,aiming at promoting the oxidative carbonylation of methanol to prepare DMC in this paper.High-activity super activated carbon-supported copper catalysts（Cu/SAC）and carbon nanotube supported copper catalyst（Cu/CNT-ALD）were designed and synthesized by impregnation method and atomic layer deposition technology,respectively.Then,the catalytic activity of these catalyst for DMC synthesis was systematically studied.Furthermore,the effective strategies to control the size effect of the active components were proposed,as well as the structure-activity relationships was revealed.The main research contents and results are as follow:（1）Cu/AC and x Cu/SAC catalysts were prepared by impregnation method using commercial activated carbon and pitch-based super activated carbon as supports,respectively.The effects of supports and Cu loading on the catalytic performance of methanol oxidative carbonylation were investigated.As compared with Cu/AC,x Cu/SAC catalysts displayed the better catalytic performance.It is mainly due to the presence of more defect sites in SAC and the strong interaction between the active component Cu and the support in x Cu/SAC,which improves the dispersion of copper nanoparticles.Especially,0.5Cu/SAC exhibited the highest catalytic performance,which was 1035 mg·g^-1·h^-1 of the DMC selectivity(S_DMC)and 146.2 h^-1 of conversion frequency（TOF）.（2）Using carbon nanotubes treated with nitric acid as supports,Cu/CNT-IMP and Cuy/CNT-ALD catalysts were prepared by impregnation method and atomic layer deposition technology respectively,and used for the methanol oxidative carbonylation reaction.The effect of the preparation method of the catalyst on the catalytic performance of the oxidative carbonylation of methanol was investigated.The results show that compared with Cu/CNT-IMP,Cuy/CNT-ALD has better catalytic performance,attributing to the presence of active species in Cuy/CNT-ALD with highly dispersion as well as smaller size of atomic clusters with narrow distribution.（3）Cuy/CNT-ALD catalysts with different Cu loading,prepared by changing the number of deposition cycles,which were employed for the methanol oxidative carbonylation reaction.Interestingly,a volcanic curve appeared the reaction performance with the number of cycles.When 10 cycles（Cu loading of 0.21 wt.%）were deposited,the catalyst has the best reaction performance,and the S_DMC and TOF are 99.3%and 186.0 h^-1,respectively,which is significantly higher than that of Cu/CNT catalyst reported in literature.This may be because as the cycles increases（>10）,the surface active sites on the CNT will decrease due to the overlap between the Cu nanoparticles,which is not conducive to the increase in activity.