Improved Catalytic Performance in Dimethyl Ether Carbonylation over Hierarchical Mordenite by Enhancing Mass Transfer

Abstract

Dimethyl ether (DME) carbonylation over mordenite (MOR) is a typical spatial confined reaction, but the superior shape selectivity is accompanied by a diffusion limitation of the microporous channel. Thus, enhancing mass transfer to improve the catalytic performance of MOR is important for its application. In this study, an unbiased chemical etching with a NH4F solution was employed to introduce secondary porosity into MOR. Through altering the etching temperature, a series of hierarchical MOR with different porosities were successfully prepared. XRD, Ar adsorption, and ICP together with the quantification of acid sites confirmed that the microporous structure and acidity of pristine zeolite were preserved after etching. The Weisz–Prater criterion was used to assess the internal diffusion limitation of DME and methyl acetate (MA). Moreover, toluene was chosen as a representative molecule in zero length column measurements, in order to explore the mass transfer of coke precursors in pristine and modified MOR. Combining the catalytic performance (i.e., TOFMA, selectivity, and deactivation rate constant) and diffusivity of molecules within MOR, we obtain insight into the influence of diffusion on zeolite-catalyzed DME carbonylation.