Synthesis of C_<2+> Alcohols from Syngas over Supported Metal Catalysts Containing Small Amounts or Rh

铱、钼等钼系催化剂活性极低，主要产物为烃类。而Ir-Mo双金属催化剂具有较高的活性，其C2+醇的选择性明显提高。在钼氧化物催化剂中形成二氧化钼，而在Ir-Mo催化剂中形成Mo金属。这表明Mo被从Ir金属迁移的氢物种还原。TPR实验表明，CO在Ir上的吸附也迁移到Mo上，CO和H2在金属Mo上发生反应，发现负载在含有少量Rh的SiO2上的Ir-Mo-Rh催化剂具有比Ir-Mo-Rh催化剂高得多的CO加氢活性。加入Rh后，对各种醇的选择性没有太大变化。催化剂制备过程中金属的浸渍方式对催化剂的活性有很大影响。考察了负载型金属催化剂对C2+醇选择性的影响，发现负载型金属催化剂中添加Li和负载型金属载体可以提高C2+醇选择性。结果表明，用该方法制备的二氧化硅负载铑催化剂具有极小的铑颗粒，并且它们的尺寸分布相当窄。该催化剂对CO加氢反应的活性远高于浸渍法制备的催化剂，对C2+醇的选择性也高于浸渍法制备的催化剂。

Monometallic catalysts, Ir and Mo, were extremely low in activity and yielded hydrocarbon as main products. On the other hand, Ir-Mo bimetallic catalyst exhibited an high activity, and an increase in the selectivity to the C_<2+> alcohols was observed on the bimetallic catalyst. Mo dioxide was formed in the Mo monometallic catalyst while Mo metal was formed in the Ir-Mo catalyst. This suggests that Mo was reduced with hydrogen species migrated from Ir metal. From the TPR experiment, it was suggested that CO adsorbed on Ir also migrates onto Mo, and that CO and hydrogen reacted over Mo metal.It was found that Ir-Mo-Rh supported on silica containing small amounts of Rh exhibited much higher activity for Co hydrogenation than Ir-Mo bimetallic catalyst. The selectivity to various alcohols did not change very much upon the addition of Rh. The activity was greatly affected by the impregnation procedure of the metals in the catalyst preparation. The increase of selectivity to C_<2+> alcohols was investigated, and it was found that use of zirconia support and the addition of Li enhanced the selectivity of C_<2+> alcohols.We proposed a novel preparation method of supported metal catalysts using microemulsions. It was found that silica-supported Rh catalyst prepared by this method had extremely small rhodium particles, and that their size distribution was appreciably narrow. This catalyst exhibited much higher activity for the CO hydrogenation than the conventional catalysts prepared by impregnation, and showed high selectivity to C_<2+> alcohols as well as the conventional catalysts.