Rh/SiO2-, Rh/La2O3-, and La2O3-promoted Rh/SiO2 catalysts were investigated by temperature-programmed reduction (TPR) and CO hydrogenation. When the La2O3-Rh/SiO2 catalysts were prepared by sequential impregnation with La impregnation as the final step, the Rh particles were partly covered by La2O3. When the impregnation sequence was reversed, and also when coimpregnation was applied, well dispersed Rh particles were formed, which showed a distinct interaction with the promoter but no covering. The presence of La2O3 shifted the TPR reduction of Rh2O3 to higher temperatures and enhanced the oxygenate selectivity in the CO hydrogenation. Catalysts exposed to air showed different TPR results and higher H2 consumptions than in situ calcined catalysts due to the presence of La carbonate. After removal of carbonate, no H2 consumption other than for the reduction of Rh3+ to Rh0 was observed, demonstrating that no reduction of La2O3 takes place. © 1993 Academic Press, Inc.
