Manganese-promoted Rh/Al2O3 for C2-oxygenates synthesis from syngas -: Effect of manganese loading

The effect of manganese promoter loading on the catalytic properties of Rh/Al2O3 catalysts (Mn/Rh = 0, 0.5, 1 and 2, atomic ratio) for the synthesis of oxygenated compounds from synthesis gas was investigated. Catalysts were characterized by means of TPR, XPS, H-2 chemisorption, FT-IR, and TPSR of chemisorbed CO. It is suggested that manganese oxide promotes CO conversion as a result of the change in the relative surface coverage of H* and C* (theta(H)/theta(C)). The manganese oxide promoter also affected the selectivity to oxygenated compounds, mainly to ethanol. The manganese promoter behaved as an electron-withdrawing, partially oxidizing the rhodium atoms at the Rh-MnO interface and thus creating new sites for CO insertion. The amount of promoter seemed to be an important parameter to achieve the highest yield of the desired reaction products. For oxygenates formation, the optimum Mn/Rh atomic ratio was found to be around 1. (C) 2003 Elsevier B.V. All rights reserved.