Ethanol dehydrogenative reactions catalyzed by copper supported on porous Al–Mg mixed oxides†
Mixed aluminum and magnesium oxides (AlMgO) prepared by means of an emulsion-mediated sol–gel method was impregnated with copper nitrate solution and used in the ethanol dehydrogenative reactions to produce acetaldehyde and ethyl acetate. The emulsified system allowed to obtain a macro–mesoporous support that resulted in an outstanding dispersion of copper. The porous catalyst was about 3 times more active than the non-porous counterpart, due to the formation on the support's surface of Cu0 together with the more active Cu+ species. In fact, the simultaneous presence of Cu+ and Cu0 were advantageous for the catalytic performance, as the turnover frequencies, were 122 and 166 h−1 for the non-porous reference catalyst and for the porous one, respectively. Both catalysts deactivated due to copper particles sintering, however the porous one deactivated less, as a consequence of the better dispersion of the Cu species on the macro and mesoporous support. Acetaldehyde was the main product, however by increasing the contact time by 6.6 times, the conversion of ethanol on the non-porous catalyst reached about 90% with a selectivity to ethyl acetate of 20% by means of the coupling reaction of ethanol and acetaldehyde. The selectivity to ethyl acetate was favoured on an increased support/copper interface that is given by larger copper particles.