Comparison of Ni2P/SiO2 and Ni/SiO2 for Hydrogenolysis of Glycerol: A Consideration of Factors Influencing Catalyst Activity and Product Selectivity

Abstract

Ni 2 P/SiO 2 and Ni/SiO 2 catalysts were prepared for the hydrogenolysis of glycerol, and their structural properties were characterized by N 2 sorption, X-ray diffraction, X-ray fluorescence, CO chemisorption, H 2 temperature-programmed desorption, and NH 3 temperature-programmed desorption. It was found that Ni 2 P/SiO 2 had a similar density of exposed Ni sites as Ni/SiO 2 , while Ni 2 P/SiO 2 had much larger amount of acid sites and surface hydrogen species than Ni/SiO 2 . Ni 2 P/SiO 2 was more active than Ni/SiO 2 in the hydrogenolysis of glycerol. This is attributed to the synergism between acid and metal sites on Ni 2 P/SiO 2 . Glycerol was mainly converted to 1,2-propanediol over Ni 2 P/SiO 2 , while it was mostly converted to not only 1,2-propanediol but also ethylene glycol and ethanol over Ni/SiO 2 . The formation of ethylene glycol and ethanol on Ni/SiO 2 is attributed to the C–C bond cleavage catalyzed by metallic Ni rather than weak acidity. In addition, temperature and H 2 pressure increase did not promote the formation of ethylene glycol and ethanol on Ni 2 P/SiO 2 . Instead they mainly promoted the further conversion of 1,2-propanediol to form 1-propanol. Thus, Ni 2 P/SiO 2 was more active for the cleavage of C–O bonds and less active for the cleavage of C–C bonds than Ni/SiO 2 . We suggest that the higher activity of Ni 2 P/SiO 2 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. 采用浸渍法及程序升温还原法制备了 Ni 2 P/SiO 2 和 Ni/SiO 2 催化剂, 利用 N 2 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, Ni 2 P/SiO 2 和 Ni/SiO 2 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. Ni 2 P/SiO 2 催化剂上主要产物为 1,2-丙二醇及 1-丙醇, 而 Ni/SiO 2 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 H 2 压力不能促进 Ni 2 P/SiO 2 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, Ni 2 P/SiO 2 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. Glycerol was mainly converted to 1,2-propanediol and 1-propanol over Ni 2 P/SiO 2 , while it was mainly converted to 1,2-propanediol, ethylene glycol, ethanol, and methane over Ni/SiO 2 .