This paper gives a review of research work in the synthesis of higher alcohols over catalysts based on Cu/ZnO/Al,O,, emphasizing three main topics: (i) the effect on selectivity of the addition of several compounds to this catalyst, (ii) the effect on selectivity of the reaction conditions used, and (iii) the reaction network leading to the different products found. Although the use of aLkali compounds has been studied most extensively, other corn~un~, for example those containing manganese, also appear to be promising additives. The process conditions are rather critical and this may cause some practical difficulties in industrial plants. An extended aldol condensation mechanism is proposed which can explain the product distribution found.
The influence of different promoters (CeG2, MnoX, K2CO3) on various properties of a standatd coprecipitated CwZnG/Al203 catalyst has been examined. The catalysts pmpared were characterixed by Cu surface area, FTIR and TPR measurements. It was found that addition of K2C03reduoedtheCusurfactarcabyabout~,whenastheCusurface~didnotdecrease with addition of the other promoters. The reduction behaviour was affected by the addition of K2CO3 as well as by MnOx, but not by CeG2. The cause of these effects is possibly an electronic interaction between the promoter and Cu ions.The effect of the different promoters on the activity and selectivity has also been studied. The K2CG3 promoted catalyst has an optimum selectivity to higher alcohols at 280 "C; addition of Mn made the catalyst more selective towards methanol. At 300 OC, the Ce promoted catalyst had a high selectivity to methanol and isobutanol. The promoting effect of the additives may be caused by stabilization of the surface intermediates leading to alcohols. Inframd measurements of adsorbed CO or adsorbed methanol on materials with and without K did not, however, provide any evidence for a difference in reactionmechanism.
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