Li Peidong, Han Qiao, Zhang Xiaomin, Yuan Yangyang, Zhang Yanfei, Xu Li, Guo Hongchen, Xu Lei
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology Dalian 116024 People's Republic of China
National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian 116023 People's Republic of China
RSC Adv. 2019 Apr 30;9(23):13234-13242. doi: 10.1039/c9ra01798d. eCollection 2019 Apr 25.
The effect of the introduced base sites in CsX with alkali oxide modification towards side-chain alkylation of toluene with methanol was systematically investigated in the present work. A series of alkali oxide modified CsX with a base properties (base strength and amount) gradient were prepared by impregnating CsX with alkali metal hydroxide. Here, CsX with different base strengths were selected as the parent zeolite, which is favorable to clarify the different types of base site in the modified CsX. The base properties of the samples were elucidated based on the CO-TPD results as well as with characterization by XPS and FT-IR of adsorbed CO. It was revealed that the base strength of the oxygen atoms with negative charge (O ) in the zeolite framework can be strengthened by the electron donating function of the alkali oxides in the supercage of CsX. Detailed analysis of the correlation between the reaction behaviors of side-chain alkylation reaction and the base properties of the indicated catalysts was carried out. It was found that the dehydrogenation of methanol to formaldehyde step was promoted by the increasing base properties of O in the CsX framework and that was the main reason for the promotion of the whole side-chain alkylation reaction. However, it was also found that the stronger base properties of the alkali oxide modified CsX would enhance the formation of active hydrogen atoms, which aggravated the unwanted styrene conversion to ethylbenzene.
本工作系统研究了引入碱金属氧化物对CsX进行改性后的碱位对甲苯与甲醇侧链烷基化反应的影响。通过用碱金属氢氧化物浸渍CsX制备了一系列具有碱性质（碱强度和碱量）梯度的碱金属氧化物改性CsX。在此，选择具有不同碱强度的CsX作为母体沸石，这有利于阐明改性CsX中不同类型的碱位。基于CO-TPD结果以及通过吸附CO的XPS和FT-IR表征来阐明样品的碱性质。结果表明，CsX超笼中碱金属氧化物的给电子作用可增强沸石骨架中带负电荷的氧原子（O⁻）的碱强度。对侧链烷基化反应的反应行为与所示催化剂的碱性质之间的相关性进行了详细分析。发现CsX骨架中O⁻碱性质的增强促进了甲醇脱氢生成甲醛的步骤，这是促进整个侧链烷基化反应的主要原因。然而，还发现碱金属氧化物改性CsX较强的碱性质会增强活性氢原子的形成，这加剧了不需要的苯乙烯转化为乙苯的过程。
