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 of the catalyst can effectively overcome these drawbacks. Unfortunately, the co-precipitation and milling methods that have been widely studied allow the addition of aluminum with low content, as high aluminum content negatively affects the catalytic performance. In this work, a novel series of high-aluminum-content Al2O3@SO42-/ZrO2 catalysts were synthesized by coating sulfated zirconia on γ-Al2O3 and applied in alkylation for removing trace olefins from reforming aromatics. Various synthesis variables, such as sulfonation concentration, sulfonation time, calcination temperature and zirconia loading, were concerned and systematically optimized. The as-synthesized Al2O3@SO42-/ZrO2 catalysts were characterized by XRD, HR-TEM equipped with EDX, N2 adsorption-desorption isotherms, EA, FT-IR, NH3-TPD and Py-FTIR technologies to determine the structural and acidic properties of the catalyst. The results further revealed the structure constructed by sulfated zirconia coated on the surface of γ-Al2O3 and the stabilization of favorable tetragonal zirconia phase even at exceedingly high aluminum content, overcoming the limitation of the co-precipitation and milling methods. Meanwhile, the synergistic effect of Al species and Zr species could promote the improvement of Brønsted acid sites. Based on these, the optimal Al2O3@SO42-/ZrO2-50% performed outstanding catalytic activity and stability, given the olefins conversion of 98%-75% during the continuous reaction experiment. The excellent regeneration performance, with olefins conversion only slightly declining after 4 consecutive reaction-regeneration cycles, was also obtained over such the catalyst, which could be due to Al promoting effects on stabilizing tetragonal zirconia phase and surface sulfur species. Besides, the mechanistic pathway for the alkylation of olefins with aromatics over Al2O3@SO42-/ZrO2 was investigated and proposed by model reaction and GC-MS characterization.

Keywords: Sulfated zirconia, Al2O3@SO42-/ZrO2, Coating structure, Alkylation, Aromatics, Olefins removal