沉淀剂对CuZnAl催化剂糠醛气相加氢制糠醇选择性的影响

采用共沉淀法制得分别以NaOH、Na_2CO_3和Na_2CO_3/NaOH为沉淀剂的CuZnAl-1、CuZnAl-2和CuZnAl-3催化剂,采用X射线衍射(XRD)、N2吸附-脱附、H_2-程序升温还原(H_2-TPR)、热重和NH_3-程序升温脱附(NH3-TPD)等方法对催化剂进行了表征,并在固定床反应器上研究了沉淀剂对CuZnAl催化剂糠醛气相加氢制糠醇选择性的影响。结果表明,糠醛加氢在三种催化剂上均有较高转化率,而CuZnAl-3催化剂对糠醇有较高选择性。沉淀剂对CuZnAl催化剂的物相结构、比表面积、酸性和氧化还原性均有较大影响。以Na_2CO_3/NaOH为沉淀剂得到的CuZnAl-3催化剂具有适宜的比表面积、CuO晶相、较弱的酸性位,且表面CuO易于还原,这些因素有利于催化反应生成糠醇。CuZnAl-3催化剂上糠醛气相加氢制糠醇优化工艺参数为:常压、反应温度180℃、氢醛物质的量比为5∶1、糠醛体积空速0.3h~(-1);糠醛转化率为99.4%,糠醇选择性为98.3%。

Effect of precipitant on the performance of CuZnAl catalysts in the gas phase selective hydrogenation of furfural to furfuryl alcohol

The catalysts of CuZnAl-1, CuZnAl-2 and CuZnAl-3 were prepared by the co-precipitation method using NaOH, Na₂CO₃ and Na₂CO₃/NaOH, respectively, as the precipitant. They were characterized by X-ray diffraction (XRD), N₂ adsorption-desorption, H₂-temperature programmed reduction (H₂-TPR), TGA, and NH₃-temperature programmed desorption (NH₃-TPD);the effect of precipitant on the performance of CuZnAl catalysts in the gas phase selective hydrogenation of furfural to furfuryl alcohol was then investigated in a fixed bed reactor. The results illustrate that all three catalysts exhibit high furfural conversion, whereas the CuZnAl-3 catalyst gives the highest selectivity to furfuryl alcohol. The precipitant has a great impact on the phase structure, surface area, acidity and redox property of the resultant CuZnAl catalysts. The CuZnAl-3 catalyst prepared with Na₂CO₃/NaOH precipitant exhibits proper specific surface area, CuO crystalline phase, weak acid sites and easily reducible CuO on the catalyst surface, which are conducive to produce furfuryl alcohol for the hydrogenation of furfural. Under the optimizing reaction condition, viz., atmospheric pressure, 180℃, hydrogen to furfural molar ratio of 5 and furfural volume space velocity of 0.3h^-1, the conversion of furfural over the CuZnAl-3 catalyst reaches 99.4%, with a selectivity of 98.3% to furfuryl alcohol.