Abstract: The Hβ zeolite was modified with different concentrations of citric acid. The textures of the modified Hβ zeolites were characterized by XRD and Ar adsorption, and the acid properties were characterized by NH3⁃TPD and Py⁃FTIR. In addition, the interaction between the pyridine molecules and the active constituent units of the Hβ zeolite was also analyzed by Py⁃FTIR. The results showed that several active sites, such as the Brønsted acid sites associated with the bridging hydroxyl groups (SiOHAl), the weak Lewis acid sites associated with EFAL hydroxyl groups and the strong Lewis acid sites associated with the three⁃coordinated Al hydroxyl species and AlO+ cations were existed in the Hβ zeolite. The synergistic effect between the EFAL and the adjacent bridging hydroxyl groups was found on the adsorption of pyridine. The pyridine molecule which adsorbed in the Lewis acid site and bonded with the adjacent B acid sites was less likely to desorb at high temperature. Pyridine molecules were preferentially adsorbed on the strong acidic bridging hydroxyls and defect sites associated with the three⁃coordinated Al hydroxyl species. It was only weakly interacted with EFAL hydroxyl groups. After citric acid treatment, EFAL hydroxyl groups were selectively removed while the framework aluminum was not severe damaged. The strong Lewis acid sites were preserved in the modified Hβ zeolite after citric acid treatment, and the strong Lewis acid sites may be related to AlO+ and the three⁃coordinated Al species of defect sites.

Key words: Hβ zeolite, Acidic modification, Active site, Cooperativity

摘要： 采用不同浓度柠檬酸对Hβ分子筛进行改性，运用XRD、Ar吸附等温线等方法对其织构性质进行表征,并通过NH3⁃TPD和Py⁃FTIR关联改性Hβ分子筛的酸性质，以吡啶为探针分子，分析吡啶分子与Hβ分子筛各活性组成单元的作用形式。结果发现，Hβ分子筛除存在与硅铝桥羟基相关的B酸中心外,还存在与非骨架铝羟基基团有关的弱L酸中心以及缺陷位处三配位的Al羟基物种和AlO+有关的强L酸中心。非骨架铝物种与临近的硅铝桥羟基间存在协同作用，吡啶分子可以吸附在其L酸中心并与临近B酸中心产生键合,在高温时不易脱附。吡啶分子会优先吸附在酸性较强的硅铝桥羟基和缺陷位处三配位的Al羟基活性位上，而与非骨架铝羟基基团作用较弱。经柠檬酸处理后，分子筛中部分非骨架铝羟基物种被选择性移除，且未对骨架铝造成严重破坏。Hβ分子筛经柠檬酸酸处理后仍存在强L酸中心，此强L酸中心的存在方式可能与AlO+和缺陷位的三配位的Al物种有关。

关键词: Hβ分子筛, 　酸性调变, 　活性位, 　协同效应