Effects of calcination atmospheres on direct synthesis of DMC from CO2 and methanol catalyzed by rod-shaped CeO2
The direct synthesis of dimethyl carbonate(DMC)from carbon dioxide(CO2)and methanol(MeOH)is a DMC preparation route that meets the requirements of green chemistry and can realize the resource utilization of CO2.Cerium oxide(CeO2)based catalysts are widely used in this reaction.The current researches focus on the effects of morphology regulation and heteroatom doping on the catalytic performance of the catalysts.The rod-shaped CeO2 precursor was prepared by hydrothermal synthesis method,and then the corresponding catalysts were obtained by calcining the precursor in different atmospheres(H2,N2,air and O2,respectively).Then the catalysts were applied to the direct synthesis of DMC from CO2 and MeOH with 2-cyanopyridine(2-cp)as dehydrating agent(adding 0.10 mol MeOH,0.05 mol 2-cp and 0.32 g catalyst,reaction at the conditions of 120℃and 5 MPa for 2 h).The effects of calcination atmospheres on the catalytic performance of catalysts were studied.The crystal structures,texture properties and morphologies of the catalysts were characterized by XRD,N2 absorption/desorption,SEM,etc.The results show that the four catalysts show no significant differences in structural properties and morphologies,and the valence of Ce on the catalysts surface is closely related to acid-base sites.The abundant defect sites on the catalysts surface enable them to have large specific surface areas and average pore sizes(specific surface area and average pore size of CeO2-air are 65.44 m2/g and 30.06 nm,respectively).The main exposed CeO2(111)crystal surface of the catalysts can promote the formation of DMC.Compared with the other three catalysts,CeO2-air exhibits the best catalytic performance due to its highest concentration of medium and strong acid-base sites and total acid-base sites,as well as the enhancement of weak acid acidity.The DMC yield and DMC selectivity of CeO2-air are 83.2%and 99.3%,respectively.
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