INFLUENCE OF THE SECONDARY MESOPOROUS STRUCTURE OF ZEOLITE ON THE PROPERTIES OF Mo/ZSM-5 CATALYSTS FOR NON-OXIDATIVE METHANE CONVERSION

The influence of the method of forming a secondary mesoporous structure in zeolites of the ZSM-5 type on the physicochemical and catalytic properties during the non-oxidative conversion of methane into aromatic hydrocarbons (benzene and naphthalene) of 4%Mo/ZSM-5 catalysts prepared on their basis was investigated. Catalysts of 4%Mo/ZSM-5 were obtained using granular zeolite without the use of a binder with a micro-mesoporous structure, zeolite treated with an aqueous solution of citric acid, and zeolite synthesized with the addition of carbon black. The obtained zeolite catalysts were studied by IR spectroscopy, X-ray diffraction analysis, low-temperature nitrogen adsorption, thermoprogrammable desorption of ammonia, high-resolution transmission electron microscopy. It is shown that the modification of zeolites with a micro-mesoporous structure by molybdenum, regardless of the method of their synthesis, leads to a decrease mainly strength and concentration of strong acid centers responsible for the process of methane aromatization. The strongest decrease in the content of strong acid centers is observed for zeolite treated with citric acid, which is associated with the dealuminization of zeolite. The study of textural characteristics showed that zeolites ZSM-5mmm and ZSM-5mmm/CA have the largest volume of mesopores than zeolite synthesized with carbon black. The morphology, particle size and the distribution of particles of the catalysts were determined by high-resolution transmission electron microscopy. Catalytic tests of the samples showed that the creation of an additional mesoporous structure in zeolites of the ZSM-5 type leads not only to an increase in the activity of 4%Mo/ZSM-5 catalysts obtained on their basis, but also to the stability of their operation. It has been found that the most effective in the process of methane dehydroaromatization is a 4%Mo/ZSM-5mmm catalyst treated with 0.3 N citric acid solution.