Synthesis Of Dimethyl Carbonate From Methanol And Carbon Dioxide By Ce Based Oxides

Dimethyl carbonate（DMC）is an important organic carbonate that has been widely used in polymer synthesis,fuel additives and organic solvents.The synthesis of DMC from CO₂ can not only realize resource utilization,but also be important for carbon emission reduction.It has been reported that various catalysts have been developed and evaluated for the synthesis of DMC,among which,the study of catalysts for effective activation of CO₂ is the key.Cerium-based oxide catalysts are thermally stable and poison resistant bifunctional catalyst,i.e.,showing both acidic and basic sites;thus its morphology,CeO₂crystalline size,and surface composition can markedly affect catalytic activity and selectivity.CeO₂ and its mixed oxides are the main active catalytic components,which exhibit superior catalytic performance in the direct synthesis of DMC from CO₂ and methanol.In this study,CeO₂ catalyst with different morphological structure were synthesized by hydrothermal method and a series of studies were carried out to investigate its catalytic performance.In addition,Fe and Zr were introduced to synthesize bimetallic mixed oxide nano-catalysts,and the samples were characterized with TEM,TPR,TPD,XRD,XPS and Raman,etc.,to study their effects on the catalytic activity of DMC.Systematic reaction parametric study was conducted to obtain the optimum process condition as 160℃,7.0 MPa and 4 h of reaction time.It was found that Fe doping had a significant contribution to the catalytic activity of CeO₂ nanorods,and the effect of Fe doping amount was further investigated.Among them,2%Fe-CeO₂ showed the best catalytic performance,and synergism between the moderate acid-base sites,specific surface area and surface composition generated by Fe doping was essential for DMC production.When Zr was impregnated,（111）crystalline facet became the popular surface CeO₂ crystalline structure and the catalytic activity depends largely on the compositional structure and properties of Zr-CeO₂.The doping of Zr facilitated the production of DMC significantly.Study of the effect of Zr loading on the catalytic performance of Zr-CeO₂ nanoparticles reveals that 5%Zr-CeO₂nanoparticles exhibited the best catalytic performance.It was found that the moderate number of acid-base sites,high specific surface area and properly small pore size were also among the important factors affecting the catalytic activity.The results suggest that the catalytic performance can be enhanced by modulating the morphology of the Cebased oxide catalysts and optimizing the reaction process conditions.And the relationship between properties such as morphology,acid-base sites,specific surface area and catalytic performance was determined to promote the activation of methanol to methoxy species as well as the activation of CO₂ adsorption.