Vapor-phase methanol and ethanol coupling reactions on CuMgAl mixed metal oxides

Authors:  Juan J. Bravo-Suárez, Bala Subramaniam, Raghunath V. Chaudhari

Abstract:
The effects of catalyst composition on methanol and ethanol coupling reactions were studied on CuMgAlO_x mixed metal oxides (MMOs). CuMgAlO_x samples with Cu contents between 4 and 38 at.% were prepared by thermal decomposition of layered double hydroxides. These MMOs contained highly dispersed CuO consisting of isolated and oligomeric CuO (number of CuO nearest neighbors between 2 and 4.5) species as determined by ultraviolet–visible spectroscopy and temperature programmed reduction techniques. The catalysts were tested at 448–523K, 0.1 MPa, alcohols gas-hourly space velocities (GHSVs) of 1000–3000 std cm³ gcat⁻¹ h⁻¹, and a feed MeOH/EtOH molar ratio of 4. Incorporation of Cu in MgAlOx solid solutions drastically changed product selectivity, formation rates, and catalyst stability. The main products on CuMgAlOx included C C coupling (e.g., C³⁺ alcohols, aldehydes, and esters), non-C C coupling (e.g., acetaldehyde, methyl formate, methyl acetate), and methanol decomposition (i.e., CO_x) products as a result of C C coupling reactions on M Al (M = Mg, Cu) and dehydrogenation, esterification, reverse methanol synthesis, and the water–gas shift reactions on Cu, respectively. The highest space-time yield of C C coupling products was 300 g kgcat⁻¹ h⁻¹, obtained with CuMgAlO_x containing 21 at.% Cu at 523K and an alcohols GHSV of 3000 std cm3 gcat⁻¹ h⁻¹. In situ Fourier transform infrared spectroscopy during MeOH + EtOH, EtOH, and MeOH reactions on CuMgAlO_x and MgAlO_x suggested that surface carboxylates (formate and acetate) are spectator species whereas oligomeric forms of formaldehyde and acetaldehyde may be responsible for the deactivation of MgAlO_x.

Keywords:
Alcohol coupling
Esterification
Layered double hydroxides
Mixed metal oxides
Infrared spectroscopy

Published in: Applied catalysis A: General  (Volume 455, Pages 1-266, 30 March 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Vapor-phase methanol and ethanol coupling reactions on CuMgAl mixed metal oxides

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