焙烧气氛对棒状CeO_(2)催化CO_(2)和甲醇直接合成DMC的影响

Effects of calcination atmospheres on direct synthesis of DMC from CO_(2) and methanol catalyzed by rod-shaped CeO_(2)

二氧化碳(CO_(2))和甲醇(MeOH)直接合成碳酸二甲酯(DMC)是一条符合绿色化学要求的DMC制备路线,并可实现CO_(2)资源化利用。氧化铈(CeO_(2))基催化剂被广泛应用于该反应,目前研究主要集中在形貌调控与杂原子掺杂对催化剂催化性能的影响。采用水热合成法制备了棒状CeO_(2)前驱体,然后在不同的焙烧气氛(分别为H_(2)、N_(2)、air和O_(2))中处理前驱体得到相应催化剂,然后将催化剂应用于2-氰基吡啶(2-cp)作脱水剂的CO_(2)和MeOH直接合成DMC(加入0.10 mol MeOH、0.05 mol 2-cp和0.32 g催化剂,在120℃、5 MPa的条件下反应2 h)中,研究了焙烧气氛对催化剂催化性能的影响。采用XRD、N2吸/脱附和SEM等对催化剂的晶相结构、织构性质和形貌等进行了表征。结果表明,4种催化剂在结构性质和形貌方面没有表现出明显差异,而催化剂表面的Ce价态与酸碱位点密切相关。催化剂表面存在的丰富缺陷位点使其具有较大的比表面积和平均孔径(CeO_(2)-air的比表面积和平均孔径分别为65.44m^(2)/g和30.06nm),催化剂主要暴露的CeO_(2)(111)晶面能促进DMC的生成。与其他3种催化剂相比,CeO_(2)-air因表面含有最丰富的中强酸碱位点和总的酸碱位点,以及较强的弱酸酸性而表现出最好的催化性能,该催化剂作用下的DMC产率和DMC选择性分别为83.2%和99.3%。

The direct synthesis of dimethyl carbonate(DMC)from carbon dioxide(CO_(2))and methanol(MeOH)is a DMC preparation route that meets the requirements of green chemistry and can realize the resource utilization of CO_(2).Cerium oxide(CeO_(2))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 CeO_(2) precursor was prepared by hydrothermal synthesis method,and then the corresponding catalysts were obtained by calcining the precursor in different atmospheres(H_(2),N_(2),air and O_(2),respectively).Then the catalysts were applied to the direct synthesis of DMC from CO_(2) 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,N_(2) 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 CeO_(2)-air are 65.44 m^(2)/g and 30.06 nm,respectively).The main exposed CeO_(2)(111)crystal surface of the catalysts can promote the formation of DMC.Compared with the other three catalysts,CeO_(2)-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 CeO_(2)-air are 83.2%and 99.3%,respectively.