Ethanol is considered as an ideal and viable alternative for transportation fuel or as a potential source of hydrogen in fuel cells. Recently, a new synthetic route of ethanol from syngas has been proposed, consisting of carbonylation of dimethyl ether (DME) to methyl acetate (MA) and MA hydrogenation. H-MOR was found as an efficient catalyst in the carbonylation of DME, in which Brønsted acid sites (BAS) serve as active centers. Numerous efforts have been devoted to exploring the relationship between the amount of acid sites and reactivity. However, few reports focus on understanding the effect of acidic strength especially in different channels on the catalytic performance. In this work, we successfully modulated the Si/Al ratios by changing the oxalic acid concentrations and treatment time, which range from 8 to 26. The results of XRD patterns, SEM and TEM images showed that all the samples preserved well-defined MOR crystal structure after post-treatment. The heat of NH3-desorption from BAS in 8-MR (ΔHdes(NH3-8MR)), as a descriptor, was calculated by a new characterization method of FTIR-TPD of NH3. The good linear correlation between TOFMA and ΔHdes(NH3-8MR) indicates that the intrinsic acid strength plays an essential role in the DME carbonlylaion reaction. Furthermore, the activation barriers for DME carbonylation was calculated on the models with varying acid strength by tuning the length of terminal Si-H bond. A linear relationship between the deprotonation energy (EDPE) and activation barriers (Eact) indicates that the MA formation rate is proportionally dependent on the acid strength of BAS in 8-MR. In summary, the reactivity of DME carbonylation over BAS at 8-MR of H-MOR with varying acid strength has been systematically investigated. Both experimental and theoretical results demonstrated that stronger acidity could enhance the reactivity for DME carbonylation, which may provide inspiration for design of highly active zeolite for Brønsted acid catalyzed reactions.

Carbonylation of dimethyl ether over H-MOR: Towards elucidating the effects of acid strength

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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