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用红外光谱法研究了C_6—C_8芳烃在HZSM-5,PHZSM-5及REY催化剂表面上的吸附物种。间二甲苯室温吸附在HZSM-5上几乎见不到表征苯环的C—C键伸缩振动吸收蜂,但出现一条很强的表征对二甲苯苯环C—C键的伸缩振动吸收峰,表明吸附的间二甲苯基本上都转化为对二甲苯。反之,室温吸附在HZSM-5上的对二甲苯也部分地转化为间二甲苯(或邻二甲苯)。吸附在HZSM-5上的邻二甲苯则部分地转化为对二甲苯。REY催化剂上的吸附,也有类似的异构化现象。甲苯室温吸附在PHZSM-5上时,却观察到对二甲苯的吸附物种,表明发生了歧化作用。甲苯室温吸附在预吸附CD_3OD的REY催化剂上发生烷基化生成了对二甲苯。此外,还观测到吸附态的C_6D_6分子的D原子与沸石催化剂表面结构的OH基发生D—H交换作用。苯在HZSM-5,PHZSM-5及REY上吸附时,其结构对称性均有不同程度的降低。
The adsorption species of C_6-C_8 aromatics on the surface of HZSM-5, PHZSM-5 and REY catalysts were studied by infrared spectroscopy. At room temperature, m-xylene adsorbed on HZSM-5 shows almost no absorption of the C-C stretching vibration of the benzene ring, but there is a strong absorption peak showing the stretching vibration of the C-C bond of p-xylene benzene ring The adsorbed m-xylene is essentially converted to p-xylene. Conversely, p-xylene adsorbed on HZSM-5 at room temperature is also partially converted to m-xylene (or o-xylene). Orthoxylene adsorbed on HZSM-5 is partially converted to para-xylene. REY catalyst adsorption, there are similar isomerization phenomenon. When toluene was adsorbed on PHZSM-5 at room temperature, paraxylene adsorbed species were observed indicating disproportionation occurred. Toluene adsorption at room temperature on the pre-adsorption of CD_3OD REY catalyst alkylation generated p-xylene. In addition, it was also observed that the D atom of the adsorbed C 6 D 6 molecule interacted with the OH group of the zeolite surface structure to generate D-H exchange. When benzene is adsorbed on HZSM-5, PHZSM-5 and REY, the structural symmetry of benzene decreases to some extent.