甘油氢解制1,2-丙二醇Cu/ZrO_2催化剂的稀土改性

Modification of Cu/ZrO_2 Catalysts by Rare Earth Elements for Catalytic Hydrogenolysis of Glycerol to 1,2-Propanediol

用等体积浸渍法制备了稀土改性的Zr O2负载铜催化剂,考察其在质量分数40%甘油水溶液进料时气相氢解制1,2-丙二醇反应的性能,并用比表面积及孔径分析仪(BET)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和氢气程序升温还原(H2-TPR)表征了催化剂的孔结构、形貌、晶相和还原性。典型的氢解反应条件为220℃、1MPa、氢与甘油的摩尔比值为100,液时空速为0.25 g甘油/(g催化剂·h)。首先在预实验中对Al2O3、Si O2和Zr O23种载体进行对比实验,发现未改性的负载铜催化剂均不稳定。浸渍Ce改性的Cu/Si O2催化剂稳定性有较大改善,但只维持700 h左右。接着考察用共沉淀法在Zr O2载体中添加稀土元素铈(Ce)、镧(La)和钇(Y)的改性效果,发现均能显著提高催化活性和选择性,而加Y稳定的氧化锆(YSZ)载体性能最佳。最后浸渍Ce对Cu/YSZ催化剂进行改性,并对Ce的含量进行了优化,结果证明,18%Cu^4%Ce O2/YSZ(均为质量分数)催化剂活性和选择性最佳,1,2-丙二醇得率超过93%。该催化剂具有开放性孔结构,比表面积达到107 m2/g,前躯体中Cu O晶粒最小,还原温度最低。对最优条件下制备的催化剂进行了长运转考察,稳定运行超过1 600 h,1,2-丙二醇收率维持在94%以上。

A series of rare earth elements promoted Cu/ZrO2 catalysts were prepared by impregnation of incipient wetness method and tested in gas-phase hydrogenolysis of glycerol to 1,2-propanediol where the 40% glycerol aqueous solution was adopted as the feed. The pore structure, morphology, crystalline phase and reducibility of the catalysts were characterized by BET, TEM, XRD and H2-TPR, respectively. The typical reaction conditions of hydrogenolysis were selected as 220 ℃, 1 MPa, molar ratio of hydrogen to glycerol 100, and liquid space velocity 0. 25 g-glycerol/（ g-catalyst · h）. Three kinds of supports, namely SiOz, A1203 and ZrO2 were screened in the preliminary tests, but all these unprompted catalysts deactivated quickly under the tested reaction conditions. The stability of Cu/SiO2 promoted by impregnation of Ce was substantially improved, but still lasted only for around 700 h. For purpose of modification, the elements of rare earths La, Ce, Y were added in ZrO2 by coprecipitation method. The performance of catalysts was obviously improved after doping of La, Ce and Y in ZrO2 support, among which, yttria stabilized ZrO2 （YSZ） was the best in activity and selectivity. Then, Ce was introduced as a promoter by successive impregnation of Cu and Ce precursors. The best catalyst was found to be 18% Cu ~ 4% CeO/YSZ, with the yield of 1,2-propanediol over 93%. Instrumental characterization revealed that this catalyst contained an open pore structure and BET specific surface area 107 m2/g, while its CuO crystal was also the smallest in size and easiest to reduce. Time-on-stream test was carried out with the thoroughly optimized catalyst, a 1,2-propanediol yield over 94% was maintained over 1600h, foreseeing a prospect of industrial application.