Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5

Abstract

The reaction mechanism of the decomposition of ethoxy species to ethene and acidic OH groups on H-ZSM-5 was studied by IR spectroscopy using isotope-labeled ethanol. The concerted mechanism occurring on both the ethoxy (acid) site and the counterpart lattice oxygen was suggested by GC-MS analysis of evolved d2-ethene and IR observation of the recovery of OH s groups on acid sites from the decomposition of CH3CD2O- ethoxy species. The concerted mechanism was further confirmed by the estimation of activation energy for decomposition of CH3CH2O-, CH3CD2O-, and CD3CD2O- ethoxy species, 122 ± 3, 125 ± 3, and 140 ± 5 kJ mol(-1), respectively, where the kinetic isotope effect was observed for the cleavage of the CH or CD bond of the methyl group of the ethoxy species.

Electrophilic aromatic substitution over zeolites generates Wheland-type reaction intermediates

“…This ethanol dehydration process does not involve the formation of any carbocation, as was computationally and spectroscopically verified by Kim et al 46 and Kondo et al 47 , respectively. However, ethylene could react further with ZeOH to form an SES (cycle A, Fig.…”

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

“…Mechanism of ethanol dehydration over ZSM-5. According to the research reports, the dehydration of ethanol to diethyl ether is represented by two different pathways, termed the associative pathway and the dissociative pathway 7,18,19 . In the associative pathway, an ethanol molecule is adsorbed at a proton site to form a hydrogen-bonded ethanol monomer ( Fig.…”

“…Besides, the rapid hydrogenation of C 4= to C 4 observed in substantial extent in the presence of paired protons on ZSM-5 (p) (C 4= /C 4 0.33 and 0.06 for ZSM-5 (s) and ZSM-5 (p) , respectively) and the formation of aromatic intermediate species (m-xylene: the 1605 cm -1 band and 1,2,4-trimethylbenzene: the 1505 cm -1 band) 36,37 (Fig. 7) points to exceptional activity for hydrogentransfer processes 7,18 . Enhanced oligomerization was also reported in 1-butene 18 and propene 4,7 reactions on ZSM-5 with Al pairs.…”

Unraveling the Homologation Reaction Sequence of the Zeolite‐Catalyzed Ethanol‐to‐Hydrocarbons Process

“…Only the first step of the ETH reaction (that is, dehydration) is relatively better understood in the literature. [8,[22][23][24][25] Unfortunately,t he rest of the reaction sequences (that is,homologation, cyclization, aromatization, and cracking) have yet to be unraveled. In particular,t he exact mechanistic routes to the origin of > C 2 even-numbered (that is,homologated products such as C 4 -butylene) and > C 2 odd-numbered (that is,n on-homologated products such as C 3 -propylene) carbon-containing hydrocarbon pool (HCP) species from C 2 -ethanol are still under scrutiny within the ETH process.T he importance of the mechanistic understanding of this industrial reaction should not be underestimated;assuch, information is crucial to maximizing yields and developing new and/or improved heterogeneous catalysts.…”