柠檬酸复合改性对多环芳烃选择性开环铂/Beta催化剂性能的影响

通过水热处理、柠檬酸处理及其复合处理对Beta分子筛进行后改性,并以改性后的载体制得铂/Beta催化剂。采用X射线衍射（XRD）、X射线荧光光谱仪（XRF）、程序升温脱附（NH₃-TPD）、红外吡啶吸附（Py-IR）、骨架铝核磁共振技术（²⁷Al MAS NMR）及骨架硅核磁共振技术（²⁹Si MAS NMR）等表征了改性前后Beta分子筛的物化性质,并考察了改性前后铂/Beta的多环芳烃选择性开环性能。结果表明,Beta分子筛在柠檬酸处理过程中可同时发生络合脱铝与骨架补铝,实现骨架铝的再分布;Beta分子筛在水热处理过程中优先脱除稳定性相对较低的Si（2 Al）处骨架铝,产生骨架缺陷的同时生成一定比例的二次介孔结构;水热-柠檬酸复合处理影响Beta分子筛骨架补铝及骨架铝再分布的效果,水热处理后Beta分子筛中存在更多的骨架缺陷,促进活性Al（OH）₂⁺物种的骨架补铝作用。当Beta分子筛采用水热-柠檬酸复合处理顺序时,骨架补铝及骨架铝再分布效果显著,样品以中强酸为主,且具有较高的B酸量与L酸量的比值,所制备催化剂的多环芳烃选择性开环活性及稳定性最优。

Effect of citric acid assisted hydrothermal dealumination on performance of Pt/Beta catalysts for selective ring opening of polycyclic aromatic hydrocarbons

Beta zeolites were post modified by hydrothermal treatment,citric acid treatment and duplex treatment,and the Pt/beta catalyst was prepared with the modified support.The physicochemical properties of the the modified and unmodified beta zeolites were characterized by X-ray diffraction（XRD）,X-ray fluorescence spectrometry（XRF）,temperature programmed desorption（NH₃-TPD）,infrared pyridine adsorption（Py-IR）,framework aluminum nuclear magnetic resonance（²⁷Al MAS NMR） and framework silicon nuclear magnetic resonance（²⁹Si MAS NMR）,and the performance of the modified and unmod-ified Pt/beta on selective ring opening of polycyclic aromatic were investigated.The results showed that dealumination and re-alumination of Beta zeolite performed in citric acid treatment,leading to framework Al redistribution.In the process of hydro-thermal treatment,beta zeolite preferentially removed the framework aluminum at Si（2Al）,which had relatively low stability,and produced framework defects and a certain proportion of secondary mesoporous structure.The hydrothermal-citric acid du-plex treatment made a difference to framework aluminum addition and redistribution of beta zeolite.After hydrothermal treat-ment,there were more framework defects in beta molecular sieves,which could promote the framework supplement of active Al（OH）₂⁺ species.When the hydrothermal-citric acid duplex treatment sequence was used for beta zeolite,the effect of frame-work aluminum supplement and framework aluminum redistribution was significant.The sample was mainly medium strong acid with a high ratio of B acid content to L acid content.The as-prepared catalyst had the best selective ring opening activity and stability for polycyclic aromatic hydrocarbons.