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

Resumo

The mechanism of the reductive dehydration of ethanol (RDE) into C₃₊ alkanes over the commercial alumina—platinum catalyst AP-64 has been investigated. The catalyst pre-reduction time has an effect on the conversion of ethanol and on that of ethylene, a possible intermediate compound in the RDE reaction. Over the catalyst reduced for 12 h, ethanol turns into a C₃-C₁₂ alkane fraction and ethylene turns into a C₃-C₁₂ olefin fraction, whose yields are 39.0 and 31.4%, respectively. Energetic parameters of ethanol chemisorption and conversion on a Pt₆Al₄ cluster have been determined by the density functional theory method using the PRIRODA 13 program. Ethanol dehydration into ethylene proceeds via the successive breaking of C-H and C-O bonds, and the rate-determining step of the process depends on the atom (Pt or Al) to which the OH group of the alcohol is coordinated. Hydroxyl group transfer from the Pt atom to the nearest Al atom is energetically favorable here. It is hypothesized that the main role of the metal-containing cluster is donation of chemisorbed ethylene to the nearest acid sites, on which the ethylene oligomerizes into a C₃-C₁₀ hydrocarbon fraction.