Selective Adsorption Processes in Mordenite-Catalysed Ethanol Dehydration

Ethanol dehydration offers a promising solution to improve the sustainability of ethene production, using biomass-derived feedstocks and a heavy-metal-free zeolite catalyst. To improve understanding of the key chemical steps in this reaction, the adsorption of key species in acid-catalysed ethanol dehydration have been investigated on Brønsted Acid (BA) sites in protonated mordenite (MOR). The strength of the BA sites has been characterised using adsorption enthalpies of NH 3 , revealing that the proximity of the zeolite framework at each BA site is important for stabilisation through van der Waals interactions. Ethanol is found to adsorb more exothermically to the BA sites than the reaction products of ethene and H 2 O, suggesting that reactant adsorption is not thermodynamically hindered. Reaction selectivity can be tuned by introduction of pyridine. Calculated pyridine adsorption enthalpies indicate that pyridine preferentially occupies specific BA sites, thereby influencing the distribution of active sites available for reaction. In particular, pyridine binds significantly stronger at 12-membered-ring BA sites, which are associated with lower ethene selectivity, than to the more selective 8-membered-ring side pocket BA sites. The results of this paper show that additives may increase reaction selectivity by controlling access to different BA sites, highlighting a potential strategy for improving the performance and versatility of zeolite catalysts.