Surface Characteristics Change of Zinc Modified H-ZSM-5 Zeolites in Methanol to Hydrocarbons Transformation Process

Abstract

The t-plot method is a well-known method for determining the volumes of micro- and/or mesoporous materials and the specific surface area of a sample by comparison with a reference adsorption isotherm of a non-porous material having a similar surface chemical composition. The article describes the applicability of the t-graph method to the analysis of the surface properties of zinc modified samples of zeolite H-ZSM-5 before and after the reactions of methanol transformation into hydrocarbons occur on them. Zeolites are widely used as catalysts in the petrochemical and refining industries. These materials contain active Bronsted acid sites, distributed within the microporous structure of zeolites, which leads to selective catalysis due to the difference in the pore shape of the zeolites used. The size, shape of the zeolite catalyst determines the catalytic performance in terms of both product selectivity and catalyst deactivation. In most zeolite catalyzed hydrocarbon conversion reactions, catalyst activity is lost due to carbon deposition. In this connection, the determination of the surface properties of zeolites is an important task that contributes to the disclosure of the physicochemical essence of the process of deactivation of zeolites. The recalculation of nitrogen adsorption isotherms using the t-plot model made it possible to determine the volume of micro and mesopores. Based on the t-graph data, it can be concluded that during the transformation of methanol into hydrocarbons, carbon accumulates on the surface of the zeolite. In this case, the predominant deposition of carbon on the surface of mesopores, due to the fact that in the process of decontamination, from 61 to 73% of the volume of mesopores is lost. The number of micropores also decreases, but the share of losses is 42–54%, which is 10–15% lower compared to the loss of mesopore volume.