The role of Mn and Li promoters in supported rhodium catalysts in the formation of acetic acid and acetaldehyde

Rh-Mn-Li/SiO2 catalysts consisting of 1 wt% Rh for the synthesis of C-2 oxygenates from syngas were studied by CO + H-2 reaction and characterized by TPR, H-2-TPD, ESR and IR techniques. The Rh-Mn-Li/SiO2 catalysts, which showed a good selectivity for the formation of acetic acid and acetaldehyde, have been found to be quite different from the Rh-V/SiO2 catalysts reported previously, which mainly promoted the formation of ethanol. Comparing with the Rh-V/SiO2 catalysts, the Rh-Mn-Li/SiO2 exhibited lower capacity of hydrogen adsorption, lower hydrogenation activity, more intense interaction of the manganese oxide with the Rh component, and more intense bands of twin-adsorbed CO (i.e. more Rh1+ ion). The good selectivity of the Rh-Mn-Li/SiO2 catalysts towards acetaldehyde and acetic acid formation were correlated to these features. (C) 1997 Elsevier Science B.V