Abstract: Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate (DMC) was carried out in a continuous flow fixed-bed reactor over MgO-modified MCM-22 molecular sieves．The MgO/MCM-22 catalysts were characterized by means of XRD，N2 adsorption-desorption and pyridine-IR．Effects of MgO loading and reaction conditions were investigated．Results indicated that a high toluene conversion can be achieved along with an obvious increase in the selectivity for p-xylene over MgO modified MCM-22 using Mg(AC)2 as precursor．The influence of various reaction conditions was studied over a 12% MgO/MCM-22 catalyst．Under the optimal conditions，i.e. reaction temperature of 653 K，n (toluene) ：n (DMC) of 4 and WHSV of 1 h－1，the conversion of toluene and the selectivity to p-xylene were 31.01% and 55.61%，respectively．

摘要： 在气相连续流动固定床反应器上，以改性的MCM-22为催化剂，对甲苯与碳酸二甲酯（DMC）的择形烷基化合成对二甲苯（PX）进行了研究。以乙酸镁为前体，采用等体积浸渍法制备了一系列MgO改性的MCM-22催化剂，并通过X射线衍射、低温N2吸附-脱附和吡啶红外光谱等手段对催化剂进行了表征。考察了MgO负载量、反应温度、甲苯与DMC摩尔配比及重时空速对甲苯与DMC烷基化反应的影响。结果显示，采用乙酸镁为前体盐，催化剂能在保持较高甲苯转化率的同时显著提高对二甲苯选择性。采用12% MgO/MCM-22为催化剂，在反应温度653 K、n(甲苯)∶n(DMC)= 4∶1，重时空速（WHSV）为1 h－1条件下，甲苯转化率为31.01%，对二甲苯选择性达55.61%。