Ni_2P/SiO_2 和Ni/SiO_2 催化剂甘油氢解反应性能比较：催化剂活性及产物选择性影响因素的探讨(英文)

Comparison of Ni_2P/SiO_2 and Ni/SiO_2 for Hydrogenolysis of Glycerol:A Consideration of Factors Influencing Catalyst Activity and Product Selectivity

采用浸渍法及程序升温还原法制备了Ni2P/SiO2和Ni/SiO2催化剂,利用N2吸附-脱附、X射线衍射、X射线荧光、CO化学吸附、氢气程序升温脱附及氨气程序升温脱附等手段对催化剂进行了表征并用于甘油氢解反应.结果表明,Ni2P/SiO2和Ni/SiO2具有相近的表面Ni密度,但前者表面酸中心和表面氢物种(包括吸附氢和溢流氢)密度明显更高,且在甘油氢解反应中的活性也更高,这与其酸性中心与金属中心之间的协同作用有关.Ni2P/SiO2催化剂上主要产物为1,2-丙二醇及1-丙醇,而Ni/SiO2催化剂上主要产物为1,2-丙二醇、乙二醇和乙醇.提高反应温度和H2压力不能促进Ni2P/SiO2上乙醇和乙二醇的生成,但促进了1,2-丙二醇进一步氢解转化为1-丙醇.由此可见,Ni2P/SiO2具有较强的C-O键断裂活性及较弱的C-C键断裂活性,这可能分别与其较多酸性中心和电子及几何结构性质密切相关.

Ni2P/SiO2 and Ni/SiO2 catalysts were prepared for the hydrogenolysis of glycerol,and their structural properties were characterized by N2 sorption,X-ray diffraction,X-ray fluorescence,CO chemisorption,H2 temperature-programmed desorption,and NH3 temperature-programmed desorption.It was found that Ni2P/SiO2 had a similar density of exposed Ni sites as Ni/SiO2,while Ni2P/SiO2 had much larger amount of acid sites and surface hydrogen species than Ni/SiO2.Ni2P/SiO2 was more active than Ni/SiO2 in the hydrogenolysis of glycerol.This is attributed to the synergism between acid and metal sites on Ni2P/SiO2.Glycerol was mainly converted to 1,2-propanediol over Ni2P/SiO2,while it was mostly converted to not only 1,2-propanediol but also ethylene glycol and ethanol over Ni/SiO2.The formation of ethylene glycol and ethanol on Ni/SiO2 is attributed to the C-C bond cleavage catalyzed by metallic Ni rather than weak acidity.In addition,temperature and H2 pressure increase did not promote the formation of ethylene glycol and ethanol on Ni2P/SiO2.Instead they mainly promoted the further conversion of 1,2-propanediol to form 1-propanol.Thus,Ni2P/SiO2 was more active for the cleavage of C-O bonds and less active for the cleavage of C-C bonds than Ni/SiO2.We suggest that the higher activity of Ni2P/SiO2 for the cleavage of C-O bonds can be ascribed to its acidity,while its lower activity for the cleavage of C-C bonds may be mainly related to its electronic and geometrical properties.