Study of the Effect of the Template Nature on the Physicochemical and Catalytic Properties of ZSM-5 Zeolites and Mo/ZSM-5 Catalysts

Abstract

We studied the effect of the nature of the structure-forming additive on the physicochemical and catalytic properties of the synthesized zeolites and catalysts prepared on their basis during the nonoxidative conversion of methane to aromatic hydrocarbons. Zeolites were synthesized by hydrothermal crystallization from alkaline alumosilica gels using hexamethylenediamine (HMDA) and ammonium bicarbonate (ABC) as templates. To create a mesoporous structure in zeolites, grade P354 carbon black was added to the reaction mixtures during synthesis. The synthesized zeolites were studied by IR spectroscopy, X-ray diffraction analysis, low-temperature nitrogen adsorption, scanning electron microscopy, and temperature-programmed desorption of ammonia. The catalytic properties of the samples were studied during the nonoxidative conversion of methane to aromatic compounds. All the synthesized samples are ZSM-5 zeolites; the addition of carbon black during their synthesis slightly affects their textural properties, increasing the volume of mesopores. The modification of zeolites with molybdenum results in a lower specific surface area and porosity. Zeolites obtained using HMDA are characterized by greater strength and a lower concentration of high-temperature acid sites compared to samples synthesized with ABC. The addition of molybdenum to zeolites lowers the strength and concentration of both types of acid sites. Mo-containing catalysts obtained from zeolites with a micro-mesoporous structure show higher activity and stability in the reaction of methane dehydroaromatization compared to microporous systems.