SYNTHESIS AND REACTIVITY OF COPPER-CONTAINING NONSTOICHIOMETRIC SPINEL-TYPE CATALYSTS

Copper-containing nonstoichiometric spinel-type (NSS) catalysts can be obtained by the calcination of coprecipitated precursors, having a high Cr or Al content. TPR tests indicate the formation of very stable Cu2+ ions up to a Cu/Cu + Zn ratio of 0.5 and 0.2 for Cr- and Al-containing samples, respectively. These ions may be identified as Cu2+ ions present in the spinel-type phase or strongly interacting with it. However, increasing the copper content seems to kinetically hinder the reduction of Al-containing samples. Furthermore, traces of either chromate or carbonate phases were found. The NSS catalysts have a very high catalytic activity in ethanol conversion, mainly to acetaldehyde, however, consistent fractions of other products (acetone, methylethyl ketone and ethylacetate) were also observed, especially for the catalysts with higher copper contents. The trivalent element influences the selectivity in these products, chromium favouring the formation of ketones and aluminum that of esters.