Home – Home – Jornals – Chemistry for Sustainable Development 2021 number 2

The physicochemical and catalytic properties of Mo/ZSM-5 catalysts for methane dehydroaromatization prepared using different (NН₄- and H-) zeolite forms and nanosized Mo powder are studied. It is shown that the properties of the samples under study depend on the initial form of the zeolite used for their preparation. According to the data of electron microscopy and EDS analysis, the morphology and elemental composition of particles in the Mo/H-ZSM-5 and Mo/NH₄-ZSM-5 samples are practically similar, and molybdenum is stabilized in the zeolite matrix in the form of the aggregates of atoms. The distribution profiles of silicon and molybdenum in the catalysts indicate that a more uniform distribution of molybdenum in the zeolite is observed for the Mo/NH₄-ZSM-5 sample. Changes in molybdenum localization after methane dehydroaromatization were revealed. Molybdenum migration to the zeolite surface was observed, with the formation of MoC _x particles up to 100 nm in size, coated with a carbon layer about 3 nm thick. It was established by means of the thermal desorption of ammonia that the concentration of strong acid sites in the catalyst prepared using the hydrogen form of the zeolite was lower than that for the catalyst prepared on the basis of the ammonium form of the zeolite. This difference in the acidic characteristics of the obtained Mo/ZSM-5 catalysts depends on the conditions of their preparation. The number of thermal treatments increased in the course of catalyst preparation using the hydrogen form of the zeolite, which resulted in the partial destruction of the zeolite crystal lattice with the formation of the Al₂(MoO₄)₃ phase. Studies of the catalytic properties of the samples showed that the Mo/ZSM-5 catalyst prepared on the basis of ammonium zeolite exhibited the highest activity in the course of the nonoxidative conversion of methane to aromatic hydrocarbons.