The effect of the concentration of lanthanum introduced into high-silica TsVN zeolite (the zeolite with HZSM-5 structure of MFI type) in methanol conversion into С2-С4 olefins and p-xylene has been investigated. Lanthanum-modified zeolite catalysts with La content 1.0-5.0 wt% were characterised by X-ray diffraction, low-temperature nitrogen adsorption, and temperature-programmed ammonia desorption. It has been shown that an increase in lanthanum content in the catalyst causes a decrease in specific surface area, total pore volume and mean pore diameter. As a result of La interaction with acidic OH groups of zeolite, the strength and amount of strong Brønsted acid sites decrease, while new stronger Lewis acid sites are formed. It has been determined that the yield of С2-С4 olefins and selectivity to p-xylene depend on the ratio of acid sites of different types, the volume and mean diameter of pores in zeolite, which are controlled by lanthanum content variation. The maxim um yield of С2-С4 olefins (33.7 wt%) from methanol at 400 °C is achieved over the catalyst modified with 5.0 wt% lanthanum. The maximum yield of xylenes (21.7-22.6 wt%) with p-xylene selectivity equal to 71.6-79.3 % is achieved over the catalyst modified with 3.0-4.0 wt% lanthanum.
Babaeva et al. (Fri,) studied this question.