Alumina-platinum catalyst in the reductive dehydration of ethanol and diethyl ether to alkanes

Mechanism of the reductive dehydration of ethanol into C3+ alkanes over the commercial alumina—platinum catalyst AP-64

“…As was demonstrated in an earlier study [11], diethyl ether in the presence of the reduced catalyst turns into a mixture of hydrocarbons whose composi tion is similar to the composition of the ethanol con version products. It is doubtful that diethyl ether forms on platinum-aluminum clusters.…”

“…3), hydroxyl groups appear on Al atoms as well. Thus, in both cases there are favorable condi tions for the formation of a strong protonic acid site, and this was indeed demonstrated experimentally [11,22]. It can be hypothesized that these protonic acid sites, which form in the course of the reaction, are the places where the olefin chain grows [23,24].…”

“…In this case, ethanol turns into an C 3 -C 12 alkane fraction, while ethylene turns into a C 3 -C 12 olefin fraction (Table 1). It was observed earlier that the hydrogen that is neces sary for alkane formation results from parallel ethanol dehydrogenation reactions [11]: С 2 Н 5 ОН → СН 4 + СО + Н 2 , СО + Н 2 О → СО 2 + Н 2 , С 2 Н 5 ОН + Н 2 О → 2СО + 4Н 2 .…”

“…The addition of hypothetical intermedi ate products of the reaction to ethanol demonstrated that a noticeable increase in the hydrocarbon fraction yield is observed upon the addition of ethylene and diethyl ether [4,9,10]. Note that diethyl ether under the same conditions turns into an alkane fraction that is similar in hydrocarbon composition to the fraction obtained from ethanol [11]. The addition of acetalde hyde does not increase the alkane yield.…”

“…These results suggest the fol lowing general scheme for ethanol conversion [13]: XAFS studies of the catalyst structure and mor phology demonstrated that, upon prolonged reductive activation of the catalyst followed by steam treatment, the Pt atoms interact with Al atoms to the point of the formation of 0.257 nm long Pt-Al bonds, which are characteristic of the Pt 2 Al intermetallide [11,14]. It was found by temperature programmed ammonia desorption that the prolonged reduction and subse quent treatment of the catalyst with steam radically change the nature of the active sites of the γ alumina support: the desorption peaks of the most common probe molecules shift to 600-650°С [11], indicating the conversion of aprotic acid sites into strong Brøn sted acid sites that are as strong as the sites of zeolite catalysts [15]. These earlier results stimulated us to carry out a theoretical study of the most likely steps of ethanol conversion into an alkane fraction, which is referred to as reductive dehydration.…”