V/Ce-Al_(2)O_(3)催化甲醇选择性氧化制备二甲氧基甲烷

Selective Oxidation of Methanol to Dimethoxymethane over V/Ce⁃Al_(2)O_(3)Catalysts

为有效改善催化剂酸性,利用共沉淀法对20V_(2)O_(5)/Al_(2)O_(3)催化剂载体进行Ce改性制备了不同CeO_(2)质量分数的双功能催化剂,并对其催化甲醇选择性氧化制二甲氧基甲烷(DMM)的活性进行了研究。由X射线衍射(XRD)、扫描电子显微镜(SEM-EDS)、傅里叶红外光谱(FT-IR)、拉曼光谱(Raman)、H_(2)程序升温还原(H_(2)-TPR)及NH_(3)程序升温脱附(NH_(3)-TPD)表征结果证实,经Ce改性后在催化剂中有效引入了中强酸位点是DMM选择性提高的关键因素,同时也增强了钒氧化物与载体间的相互作用,降低了催化剂的氧化还原性。实验结果表明,当CeO_(2)质量分数为8%时,催化剂表现出最佳的催化性能,反应温度对甲醇氧化产物有较大影响,低温更有利于DMM的生成。在反应温度为170℃时,经20V/8Ce-Al_(2)O_(3)催化,甲醇转化率为23.6%,DMM选择性达99.9%。催化剂经循环反应5次后DMM选择性依然为99.9%,研究为改善催化剂酸性提供了有价值的参考。

Bifunctional 20V/Ce-Al_(2)O_(3)(mass percent 20%V_(2)O_(5))catalysts are prepared by simply co-precipitation of 20V_(2)O_(5)/Al_(2)O_(3)with Ce to improve the acidity of catalyst effectively,and tested for partial oxidation of methanol.The structural properties are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM-EDS),Ramanspectroscopy(Raman),H_(2) temperature-programmedreduction(H_(2)-TPR)and NH_(3) temperature-programmed desorption(NH_(3)-TPD)techniques,respectively.The characterization results confirm that the incorporation of Ce in catalyst enhances the surface acidity,which is the key factor to improve the selectivity of DMM,and the interaction between vanadium oxide and the support is enhanced and the redox ability of the catalysts is reduced at the same time.The experimental results show that the catalyst 20V/8Ce-Al_(2)O_(3)with mass percent 8%CeO_(2)exhibits the best catalytic performance and the reaction temperature has a great influence on the methanol oxidation products.Low temperature is more favourable for the formation of DMM.For the catalyst 20V_(2)O_(5)/8Ce-Al_(2)O_(3),the methanol conversion and the DMM selectivity are 23.6%and 99.9%at 170℃,respectively.The selectivity of DMM is 99.9%after 5 runs.The study provides valuable reference for improving the acidity of catalyst.