(532b) Selective Adsorption of Manganese Onto Rhodium for Optimized Mn/Rh/SiO2 Alcohol Synthesis Catalysts

Using supported rhodium-based catalysts to produce alcohols from syngas provides an alternative route to conventional fermentation methods. When left unpromoted, Rh catalysts have a strong selectivity towards methane. However, promotion with early transition metal elements has been shown to be effective to increase alcohol selectivity. Therefore, a key design objective is to increase the promoter-metal interaction to maximize their effectiveness. This can be achieved by the use of the Strong Electrostatic Adsorption (SEA) synthesis method, which utilizes pH control to steer the promoter precursor (in this case MnO₄^-) onto Rh oxide supported on SiO₂. Mn promoted catalysts were created using both SEA and traditional dry impregnation (DI) and subsequently characterized by STEM and EXAFS.  The reduction behavior of the catalysts was also obtained by XANES and TPR. Reactivity results for CO hydrogenation showed significant improvement of ethanol selectivity is achieved when the promoter was prepared by SEA in comparison of promoter prepared by DI, suggesting that intimate interaction between the promoter and the active metal is critical for high selectivity.