Oxidized K-Mo catalysts supported on 7-A12O3 or SiO2 were prepared by impregnating the supports with KCl and ammonia heptamolybdate solutions and calcination at 500 ℃Unsupported oxidized K-Mo catalyst was prepared by mixing KCl and ammonia heptamolybdate compounds and calcination at 500 ℃ Both the supported and unsupported catalysts were recalcined at 800 ℃. These samples were sulfided for mixed alcohols synthesis from syngas. It is found that for 500 ℃ calcined samples, the selectivity to mixed alcohols is enhanced in the order of K-MoOa/γ-Al2O3<K-MoO3/SiO2 < K-Mo catalyst. So the chararterization of the support show obvious influence on the catalytic reaction for mixed alcohols synthesis. For 800 ℃ recalcined catalysts, the selectivity to mixed alcohols is similar for the three catalyst samples, the characterization of the support show much weak influence on the catalytic property.
The acidities of these catalysts were measured with ammonia adsorption and TPD. It is found that low selectivity to mixed alcohols for supported catalysts, by calcination 500 ℃, can be due to that part of acid sites on the supports are still existed, which decompose some of the alcohols during the reaction. With recalcination at 800 ℃, the selectivity to mixed alcohols for supported catalysts become increased, which is due to that stronger interaction between the potassium component and the support suppresses more acid sites. This idea is supported by the activities for ethanol decomposition over both the oxidized and the sulfided catalysts. It is concluded that the surface acidity of the catalysts is important for the reaction tendency to form alcohols or to form hydrocarbons from CO hydrogenation.