金属改性对多环芳烃选择性开环Pt/Beta催化剂性能的影响

以离子交换法对Beta分子筛进行Mg、Ce、Ga金属改性，并制得不同金属改性的Pt/Beta催化剂。本文采用XRD、XRF、NH₃-TPD、Py-IR、H₂-O₂、TEM、H₂-TPR、H₂-TPD及XPS等手段表征了改性前后样品的物化性质，并考察了改性前后样品的多环芳烃选择性开环性能。结果表明，改性金属对B酸中心的取代效应和对L酸中心的补偿效应，可显著调控分子筛酸性位的类型与强度。改性金属可增强金属-载体强相互作用（SMSI），一方面促进贵金属铂的分散，提高铂纳米颗粒的热稳定性；另一方面产生铂纳米颗粒向载体的电子偏移或离域，影响H₂在铂纳米颗粒上的活化与脱附。此外，金属Ga可以选择性毒化铂纳米颗粒的活性位。改性金属显著影响Pt/Beta催化剂转化甲基萘的活性、稳定性及轻芳烃选择性，金属Ga、Ce改性可显著提高催化剂的稳定性，Ga改性催化剂的轻芳烃选择性最优。

Effects of metal modification on the performance of Pt/Beta catalysts for selective ring opening of polycyclic aromatics

Beta zeolites were modified by Mg, Ce and Ga metals using ion exchange method, and Pt/Beta bimetallic catalysts were prepared by impregnation method. The physicochemical properties of these catalysts were characterized by XRD, XRF, NH₃-TPD, Py-IR, H₂-O₂, TEM, H₂-TPR, H₂-TPD and XPS, and their performances on selective ring opening of polycyclic aromatics were investigated. The results showed that the acidities of the Beta zeolites could be regulated by the metal's substitution effects on Br?nsted acid and compensation effects on Lewis acid. The strong metal-support interaction (SMSI) was enhanced by metal modification, which could promote the dispersion of platinum and improve the thermal stability of platinum nanoparticles. The migration or delocalization of electron between platinum nanoparticles and supports caused by the strong metal-support interaction (SMSI), could affect the activation and desorption of H₂ by platinum nanoparticles. In addition, the active sites of Pt nanoparticles could be selectively poisoned by the modification of Ga. Metal modification had great influence on the catalytic performance of the Pt/Beta catalysts in selective ring opening of methylnaphthalene. The stability of the Pt/Beta catalysts could be significantly improved by the modification of Ga and Ce. Besides, the Pt/Beta catalysts modified by Ga had the best selectivity.