The effect of hydrothermal pretreatment on the catalytic performance of Zn/HZSM-5 catalysts for ethylene aromatization reaction

To address the issue of coking and deactivation of Zn/HZSM-5 catalysts used for light olefins aromatization, a high-temperature hydrothermal method was employed for catalyst pretreatment. The catalysts were characterized using XRD, N₂ physical adsorption-desorption, NH₃-TPD, Py-FTIR, XPS and TG techniques. The effect of high-temperature hydrothermal pretreatment on the catalytic performance and stability of the catalyst was investigated using ethylene aromatization as a probe reaction. The results showed that the Zn/HZSM-5 catalyst exhibited excellent catalytic performance after 48 h of high-temperature hydrothermal pretreatment. Although the conversion of ethylene slightly decreased, the catalyst lifetime was significantly extended, increasing from 72 to 216 h, while the aromatics selectivity remained above 60%. It was suggested that the hydrothermal treatment enhanced the interaction between ZnO species and Brønsted acid sites, promoting the generation of ZnOH⁺ species. This not only suppressed the hydrogen transfer reaction but also significantly enhanced the dehydrogenation performance of the catalyst, improving the selectivity towards hydrogen. Additionally, the catalyst exhibited increased carbon capacity and reduced carbon deposition rate after hydrothermal treatment, demonstrating excellent anti-coking properties.