PREPARATION, PROPERTIES AND CATALYTIC ACTIVITY IN THE METHANOL SYNTHESIS OF SPINEL-TYPE CATALYSTS

Cu-containing non-stoichiometric spinel-type (NSS) catalysts can be obtained by calcination of coprecipitated precursors having a high Cr- or Al-content, with the formation also of CuO for high copper contents. In all cases, the Al-containing samples exhibit a higher surface area and a lower pore volume than those with chromium. TPR tests reveal the formation of 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, the Al-containing catalysts exhibit a lower catalytic activity than that of the corresponding Cr-catalysts, and, furthermore, a higher tendency towards hydrocarbon formation, which increases as temperature and the copper content increase, and which is favoured by reaction gas mixtures richer in hydrogen and not containing CO2.