New Findings in Hydrothermal Deactivation Research on the Vanadia-Selective Catalytic Reduction Catalyst

Disposal of spent V2O5-WO3/TiO2 catalysts: A regeneration principle based on structure-activity relationships from carrier transformations

Characterization and evaluation of hazardous spent V2O5-WO3/TiO2 catalysts are critical to determining their treatment or final disposal. This study employs a thermal approach to simulate the preparation of spent catalysts derived from commercial V2O5-WO3/TiO2 catalysts and investigate the structure-activity relationship of the carrier changes during the deactivation process. The results indicate that the catalyst carrier undergoes two processes: an increase in grain size and a transformation in crystal structure. Both structural and catalytic investigations demonstrate that the grain size for catalyst deactivation is 24.62 nm, and the formation of CaWO4 occurs before the crystalline transformation. The specific surface area is susceptible to an increase in grain size. The reactions of selective catalytic reduction involve the participation of both Brønsted acid and Lewis acid sites. The deactivation process of the carrier initially affects Brønsted acid sites, followed by a reduction in Lewis acid sites, resulting in a decline in NH3 adsorption capacity and oxidation. Correlation analysis reveals that changes in the physicochemical properties of the catalyst reduce the NO conversion, with the order being The grain size > Total acid amount > The surface area. It is recommended to recycle the spent catalyst if the carrier grain size is less than 25 nm. The findings of this investigation contribute to expanding the database for evaluating and understanding the physicochemical properties of spent catalysts for disposal.

Hydrothermal Aging Mechanism and Modeling for SCR Catalysts

Based on the activity evaluation and characterization test, we explored the hydrothermal aging mechanism of a vanadium-based SCR catalyst and constructed a dual-site hydrothermal aging kinetic model in this study. The vanadium-based catalyst contains Brønsted acidic sites and Lewis acidic sites, which show different sensitivities to hydrothermal aging, and the reduction of active sites is the main reason for the NOx conversion efficiency reduction after hydrothermal aging. The ammonia storage capacities of both sites have a high correlation coefficient with the NOx conversion efficiency. Based on the method of NH₃-TPD curve peak resolution, we quantified the transformations of the two active sites and established the relationship between the site density, the aging temperature, and the duration to determine the aging factor. Then, a hydrothermal aging kinetic model was constructed, and the parameter identification and verification of the model were carried out through flow reactor experiments. The results show that the model constructed in this study can accurately reflect the catalyst activity after hydrothermal aging.