A Supramolecular View on the Cooperative Role of Brønsted and Lewis Acid Sites in Zeolites for Methanol Conversion.

Simon Bailleul, Irina Yarulina, Alexander E J Hoffman, Abhay Dokania, Edy Abou-Hamad, Abhishek Dutta Chowdhury, Giovanni Pieters, Julianna Hajek, Kristof De Wispelaere, Michel Waroquier, Jorge Gascon, Veronique Van Speybroeck

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80 Scopus citations


A systematic molecular level and spectroscopic investigation is presented to show the cooperative role of Brønsted acid and Lewis acid sites in zeolites for the conversion of methanol. Extra-framework alkaline-earth metal containing species and aluminum species decrease the number of Brønsted acid sites, as protonated metal clusters are formed. A combined experimental and theoretical effort shows that postsynthetically modified ZSM-5 zeolites, by incorporation of extra-framework alkaline-earth metals or by demetalation with dealuminating agents, contain both mononuclear [MOH]+ and double protonated binuclear metal clusters [M(μ-OH)2M]2+ (M = Mg, Ca, Sr, Ba, and HOAl). The metal in the extra-framework clusters has a Lewis acid character, which is confirmed experimentally and theoretically by IR spectra of adsorbed pyridine. The strength of the Lewis acid sites (Mg > Ca > Sr > Ba) was characterized by a blue shift of characteristic IR peaks, thus offering a tool to sample Lewis acidity experimentally. The incorporation of extra-framework Lewis acid sites has a substantial influence on the reactivity of propene and benzene methylations. Alkaline-earth Lewis acid sites yield increased benzene methylation barriers and destabilization of typical aromatic intermediates, whereas propene methylation routes are less affected. The effect on the catalytic function is especially induced by the double protonated binuclear species. Overall, the extra-framework metal clusters have a dual effect on the catalytic function. By reducing the number of Brønsted acid sites and suppressing typical catalytic reactions in which aromatics are involved, an optimal propene selectivity and increased lifetime for methanol conversion over zeolites is obtained. The combined experimental and theoretical approach gives a unique insight into the nature of the supramolecular zeolite catalyst for methanol conversion which can be meticulously tuned by subtle interplay of Brønsted and Lewis acid sites.
Original languageEnglish (US)
Pages (from-to)14823-14842
Number of pages20
JournalJournal of the American Chemical Society
Issue number37
StatePublished - Sep 9 2019

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We acknowledge the Research Foundation - Flanders (FWO), the Research Board of Ghent University (BOF), and funding from the European Union’s Horizon 2020 research and innovation program (consolidator ERC Grant Agreement No. 647755 – DYNPOR (2015–2020)). The computational resources and services used were provided by Ghent University (Stevin Supercomputer Infrastructure) and the VSC (Flemish Supercomputer Center), funded by the Research Foundation - Flanders (FWO).


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