焙烧温度对Cu/Mg/Al催化剂催化纤维素转移加氢液化的影响

固定Cu/Mg/Al物质的量比15∶60∶25,采用共沉淀法制备Cu/Mg/Al水滑石前驱体,经过不同温度焙烧制得一系列用于纤维素在高温高压甲醇中转移加氢液化的催化剂.采用XRD、TG/DTG、BET、H2-TPR和FT-IR等表征手段研究了焙烧温度对Cu/Mg/Al水滑石衍生催化剂性能的影响.结果表明水滑石经过450 ℃焙烧后,热分解较为完全,CuO与载体MgO之间相互作用良好,具有优异的稳定结构,且CuO易还原,催化性能好.当焙烧温度450 ℃,催化剂结晶效果差,稳定性差,导致催化剂活性低.而焙烧温度450 ℃时,催化剂中CuO因为高温发生团聚,并且高温(≥650 ℃)焙烧后起隔离分散作用的尖晶石MgAl2O4稳定性较差,在参与纤维素液化的高温高压反应过程中会发生分解,导致CuO发生二次团聚;此外催化剂还会发生烧结现象使催化剂活性降低.

Effect of calcination temperature on the transfer hydrogenation liquefaction of cellulose over Cu/Mg/Al catalysts

A series of Cu/Mg/Al based catalysts were prepared by calcination of the Cu/Mg/Al hydrotalcite precursor which was synthesized by the co-precipitation method with the same Cu/Mg/Al molar ratio of 15∶60∶25 at various temperatures.The catalysts were characterized by XRD,TG/DTG,BET,H2-TPR and FT-IR to explore the effect of calcination temperature on the transfer hydrogenation liquefaction of cellulose over Cu/Mg/Al catalysts.The results showed that Cu/Mg/Al hydrotalcite was almost completely decomposed at 450 ℃.It has a good stability because of the proper force between CuO and MgO and an excellent catalytic activity because of the uniformity of CuO at such a temperature.Poor crystallization and stability were the reasons which lead to the decrease of the catalyst activity when the calcination temperature is less than 450 ℃. Higher calcination temperature (450 ℃) resulted in the agglomeration of CuO.MgAl2O4 which produced at high calcination temperature(≥650 ℃) and played a role in separating CuO decomposed in the high temperature and pressure reaction of liquefaction of cellulose,thus causing a second agglomeration.High calcination temperature also resulted in the sintering of metal oxides,thereby decreasing the catalyst activity.