金属修饰的Mg-Al复合氧化物催化氨基甲酸甲酯和甲醇合成碳酸二甲酯

Synthesis of Dimethyl Carbonate From Methyl Carbamate and Methanol Over Metal-Modified Mg-Al Mixed Oxides

以共沉淀法制备了一系列金属改性的Mg-Al类水滑石(HTlc),经500℃煅烧,获得各种金属修饰的Mg-Al复合氧化物(CHT-0.3M-500,M=Mn、Ni、Zn、Y或La)催化剂,借助XRD、SEM、N_2吸/脱附和CO_2-TPD等手段对其物理化学性质进行表征,在釜式反应器中考察其催化氨基甲酸甲酯(MC)和甲醇合成碳酸二甲酯(DMC)的反应性能。以Y修饰的Mg-Al复合氧化物为模板催化剂,考察了Y掺杂量和前驱体煅烧温度对催化性能的影响,并优化了反应条件。结果表明:CHT-0.3M-500样品表面碱性质与所掺杂金属的种类有关,催化剂活性与其表面碱性位的总数目成正比;在各种催化剂中,CHT-0.3Y-500具有最大的碱密度,因而其催化能力最高,在反应温度为200℃、反应时间为6 h、催化剂用量为0.5 g的条件下DMC收率最高可达58.3%;此外, CHT-0.3Y-500催化剂具有良好的重复使用性和催化稳定性。

A series of metal-modified Mg-Al hydrotalcite-like compounds (HTlc) were synthesized via co-precipitation method.Through calcination of the above HTlc precursors at 500 ℃,different metal-modified Mg-Al mixed oxide catalysts (i.e.,CHT-0.3M-500,where M=Mn,Ni,Zn,Y or La) were obtained.Then,their physicochemical properties were characterized by different techniques,i.e.,XRD,SEM,N2 adsorption/desorption and CO 2-TPD.Furthermore,their catalytic performances were evaluated in an autoclave reactor for the synthesis reaction of dimethyl carbonate (DMC) from methyl carbamate and methanol.The impact of Y content and precursor calcination temperature on the catalytic performance was studied over Y-modified Mg-Al mixed oxide,and the optimal reaction conditions were also determined.It was observed that the surface basic property of CHT-0.3M-500 is closely related to the type of metal element that is incorporated in the catalysts.The experimental results also showed that the catalytic activities are proportional with the total amounts of surface basic sites.Among all the catalysts,CHT-0.3Y-500 exhibits the best catalytic performance due to its high basic density.Under the following reaction conditions,i.e.,reaction temperature 200 ℃,reaction time 6 h and catalyst amount 0.5 g,the DMC yield can reach the maximum value of 58.3%.Furthermore,experimental results indicate that the CHT-0.3Y-500 catalyst exhibits good catalytic reusability and stability.