| Dimethyl carbonate (DMC), as an environmentally eco-friendly non-toxicgreen chemical, has a broad application prospect as the carbonylating andmethylating agent, lithium battery electrolytes, and fuel additives, etc. Oxidativecarbonylation of methanol, which is related to its green chemical synthesis, lowcost and abundant raw materials, has been an important new coal chemicalindustry technology. At present, active carbon supported chloride-containingcatalysts, CuCl2-PdCl2bimetallic chlorides and chlorine-free zeolite-basedcatalysts are the main catalysts. Because of the corroisive problem, thedevelopment of a new kind of good performance and environmental catalysts forDMC synthesis is necessary. It has been found that CuY zeolite catalyst is oneof the main catalysts, which is applied in this DMC synthesis reaction.It is notable that zeolite porous structure plays a significant role in thesynthesis of DMC by oxidative carbonylation of methanol. However, Y zeoliteis a microporous zeolite which consists of the supercage, sodalite cages andhexagonal prisms of the microporous structure. And even though in manyreactions microporous structure provides excellent shape-selective property, butits smaller channel diameter of0.74nm not only hinders the large moleculesinto the internal pore of Y zeolite to catalytically react with active center, butalso hinders the diffusion of reactants and products. So the preparation of Yzeolite containing mesopores is of great significance to improve the effect of catalytic reaction. Because the mesopores can shorten the diffusion path andincrease interaction probability bettween the active center with reactantmolecules of methanol and CO, which improve the utilization rate of the activecenter and is advantageous to the reactants and products molecular diffusion inthe pore. The methods of preparing multistage aperture zeolite with microporousand mesoporous have been widely studied. Our preliminary investigations aboutpreparation methods of CuY catalyst showed that CuY catalyst prepared byliquid ion exchange exhibited highest catalytic activity. On this basis, this paperinvestigates the effects of acid treatment on porous structure and oxidationcarbonylation performance of CuY catalysts supported by NaY zeolites；thenfurther examines the effects of NaOH treatment on porous structure andoxidation carbonylation performance of CuY catalysts supported by NaYzeolites. Combined with N2adsorption-desorption, TEM, XRD,29Si MAS NMR,NH3-TPD, PyIR, H2-TPR and AAS, the porous structure and methanol oxidationcarbonylation performance of CuY catalysts are studied, and the mainconclusions are as follows:(1) The catalytic activity of CuY catalyst supported by NaY zeolite treatedwith oxalic acid were effectively improved in the oxidative carbonylation ofmethanol processes. Among the catalysts studied, the CuY-4-0.2catalystexhibits the highest catalytic activity that DMC space-time yield and methanolconversion rate have been higher78.4%and61.9%respectively than thecatalytic activity of untreatmented CuY catalysts.(2) In the process of oxalic acid treatment, about4nm mesopores havebeen found, and mesoporous volume increases to0.079cm3/g, and the specificsurface area increased from30m2/g to125m2/g simultaneously.(3) The catalytic activity of CuY catalyst supported by NaY zeolitetreatmented with NaOH were also effectively improved in the oxidativecarbonylation of methanol processes. Among the catalysts studied, the CuY-0.2catalyst exhibits the highest catalytic activity that DMC space-time yield, DMC molar selectivity and methanol conversion rate have been higher96.9%，7.4%and122.2%respectively than the catalytic activity of untreatmented CuYcatalysts.(5) The total acid amount of CuY catalysts supported by NaY zeolitestreated with oxalic acid significantly decreased a lot, but the total acid amount ofCuY catalysts supported by NaY zeolites treated with NaOH is slightly reduced.(6) About4nm mesopores formed by acid and alkali treatment can promotethe accessibility of active sites and the diffusion of reactants and productsmolecules, which help increase the catalytic activity of oxidative carbonylationof methanol reaction. |
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