The proximity of aluminium atoms influences the reaction pathway of ethanol transformation over zeolite ZSM-5

Abstract

The organization of aluminium atoms in zeolites affects their catalytic properties. Here we demonstrate that the aluminium distribution is a key parameter controlling the reaction pathway of acid catalysed reactions over ZSM-5 zeolites. We study ethanol transformation over two ZSM-5 samples with similar Si/Al ratios of~15, and with aluminium atoms located mainly at the channel intersections but differently distributed in the framework. One of the samples contains mostly isolated aluminium atoms while the other has a large fraction of two aluminium atoms located in one ring. The FT-IR time-resolved operando study, supported by catalytic results, reveals that the reaction pathway in ethanol transformation over ZSM-5 is controlled by the proximity of aluminium atoms in the framework. ZSM-5 containing mostly isolated Al atoms transforms ethanol in the associative pathway, and conversely ZSM-5 containing a dominating fraction of two aluminium atoms in one ring transforms ethanol in the dissociative pathway.

Identification of an efficient adsorbent for ethanol sensing at room temperature using quartz crystal microbalance

“…4 (c)). The occurrence of protonated ethanol dimers through ethanol dehydration on zeolitic catalysts was confirmed in previous reports [47][48][49].…”

“…Based on experimental investigation, an ethanol sensing mechanism is proposed and schematized in Fig. 7, where steps (i) to (iv) are devoted to the adsorption process and steps (v) to (vii) including The formation of protonated ethanol dimers was confirmed in previous studies during ethanol dehydration on zeolite catalysts [48,60,61]. The ethoxy group can transform whereas acid sites are regenerated and as a result can provide ethylene [62,63].…”

Analysis and control of acid sites in zeolites

“…The polarization ability of anions together with OHon the N atom charge decreases in the order OH -> Cl -> PO4 3-> NO3 -: the lower the positive charge on the N atom, the lesser population of Al pairs and higher incorporation of single Al atoms sited in the vicinity of TPA + . Two ZSM-5 samples of similar Si/Al ratio (≈ 15) were prepared from dry amorphous aluminosilicate precursors with the assistance of TPAOH as OSDA [184]. Silica sol was employed as the Si source, and in the sample ZSM-5(p) Al source was aluminium butoxide while in the ZSM-5(s) polyaluminium chloride PAX-18 was used.…”

“…Besides, the adjacent Brønsted sites facilitate the dimerization and hydrogen-transfer reactions. The data suggest that the regeneration of Brønsted acid sites at higher temperatures takes place via releasing of ethane [184]. Another study reports the synthesis of two series of ZSM-5 zeolite materials with silica sol and tetraethylorthosilicate (TEOS) as the silicon source.…”

Development of a New Ternary Al2O3–HAP–Pd Catalyst for Diethyl Ether and Ethylene Production Using the Preferential Dehydration of Ethanol

“…Besides, Sarve et al, reported that some of the ethylene molecules adsorbed on Lewis acid sites and metallic sites of the Al20-HAP80-Pd catalyst act as an intermediate for diethyl ether. According to the research works, ,, the dehydration of ethanol to diethyl ether is represented by two different pathways, termed the dissociative pathway and associative pathway (Scheme b). The dissociative pathway occurs by one ethanol molecule adsorbed on the catalyst and followed by water molecule elimination to obtain the adsorbed ethoxide.…”