Alkylation for removing trace olefins from reforming aromatics over novel Al2O3@SO42-/ZrO2 catalysts derived from the ZrO2-coated γ-Al2O3 strategy

Abstract

Sulfated zirconia, as a promising catalyst in various acid-catalytic reactions, still suffer from unsatisfactory catalytic stability and regeneration performance due to severe leaching of sulfur species, while aluminum modification can effectively overcome these drawbacks. Unfortunately, the limited acceptability of aluminum content by co-precipitation and milling methods remains a critical issue. Herein, an effective strategy of coating sulfated zirconia on the surface of γ-Al2O3 was developed to synthesize the novel Al2O3@SO42-/ZrO2 catalyst with high aluminum content. The synthesis variables were investigated and systematically optimized. The structural and acidic properties of Al2O3@SO42-/ZrO2 were determined by XRD, HR-TEM equipped with EDX, N2 adsorption-desorption isotherms, EA, FT-IR, NH3-TPD and Py-FTIR. Results indicated that the unique structure constructed by sulfated zirconia coated on γ-Al2O3 not only realized the stabilization of favorable tetragonal zirconia phase even at exceedingly high aluminum content but also promoted Brønsted acid sites. Accordingly, the optimal Al2O3@SO42-/ZrO2-50% performed outstanding catalytic activity and stability, given the olefins conversion of 98%-75% during the continuous reaction experiment. Owing to the alleviation of sulfur loss by Al-promoting effects, excellent regeneration performance, with olefins conversion only slightly declining after 4 consecutive reaction-regeneration cycles, was also obtained. The mechanistic pathway for the alkylation of olefins with aromatics over Al2O3@SO42-/ZrO2 was also investigated and proposed by GC–MS analysis.