金属前躯体溶剂对Pt/ZSM-22催化剂临氢异构性能的影响

将Pt前驱体分别溶解于水、乙醇、丙酮、乙酸中,采用浸渍法制备了一系列成型Pt/ZSM-22催化剂。通过XRD、BET、TEM、CO-chemisorption、CO-FTIR和Py-FTIR等表征手段对催化剂的物相结构、织构性质、金属性质和酸性进行了系统地考察并以正十二烷为模型化合物,研究了前躯体溶剂对临氢异构反应性能的影响。结果表明,溶剂极性是造成Pt分散差异的主要原因;以乙醇、丙酮和乙酸为浸渍溶剂制备的催化剂,Pt多分布于ZSM-22分子筛上,并与酸性位相互作用造成Pt缺电子;而以水为溶剂则造成Pt多分布于氧化铝黏结剂上,对Pt的电子性质影响较小。在临氢异构反应中,与Pt落位于氧化铝相比,Pt分布于ZSM-22分子筛上表现出更高的活性和异构选择性,表明缩短酸性位与金属位间距可使反应物和异构中间体迅速扩散至金属位上发生脱氢和加氢反应。

Effect of metal precursor solvent on n-dodecane isomerization of Pt/ZSM-22

A series of Pt/ZSM-22 bifunctional catalysts were prepared by using different metal precursor solvents including water, methanol, acetone and acetic acid. The phase structure, texture properties, metal properties and acidity were systematically investigated by XRD, BET, TEM, CO-chemisorption, CO-FTIR and Py-FTIR. The effect of metal precursor solvents on n-dodecane isomerization was also studied. The results indicate that the solvents with different polarities lead to different locations of Pt particles. Part of Pt particles locate on ZSM-22 when methanol, acetone and acetic acid are used as solvents, and the interaction between Pt and acid sites lead to the electron-deficient of Pt. However, the Pt particles almost locate on the Al₂O₃ binders when water is used as solvent, and their electronic properties are little affected. Higher activity and selectivity are achieved when Pt particles locate on ZSM-22 in the n-dodecane isomerization reactions. These results indicate that shorten the distance between acid sites and metal sites can expedite the diffusion of reactants and isomerized intermediates to proceed dehydrogenation and hydrogenation reactions.