Carbon monoxide hydrogenation over alkali-promoted Rh/Al2O3, Rh/V2O3/SiO2 and Rh/ThO2/SiO2

Addition of Li, Na, K and Cs to a 1.5 wt% Rh/Al,O, catalyst resulted in a decrease of the hydrocarbon formation rate, while the methanol formation rate was almost unaffected. The overall result is an increased oxygenate selectivity at a decreased total activity. The oxo-selectivity increased in the order unpromoted < Li < Na< K < Cs. The results suggest that the main role of the alkali promoter is to decrease the carbon monoxide dissociation reaction. Rh/SiO, catalysts promoted with ThO, or V,O, had higher C&-oxygenate selectivities and a higher activity than a Rh/Si02 catalyst. Addition of Li, Na, K and Cs did not increase the oxoselectivity of the ThO,and V,O,-promoted Rh/SiO, catalysts. Independent of the kind of alkali added, it mainly decreased the activity and lowered the hydrogenation rate, suggesting that the added alkali blocked the special perimeter sites which are held responsible for the ThO, and V,O,, promotion effect or that the added alkali formed a mixed oxide with the promoter oxide. Alkali ions, therefore, did not improve the catalytic behaviour of the ThO,and V,O,-promoted Rh/SiO, catalysts.