Homogeneous catalysis of water-gas shift reaction in emulsions

Abstract

The homogeneous catalysis of the water-gas shift reaction, H 2O + COH 2 + CO 2,has been demonstrated for a number of metal carbonyl complexes under alkaline conditions in toluene-water emulsions. Mo(CO) 6, W(CO) 6 and Ru 3(CO) 12 were found to be effective catalysts at temperatures below 200 °C. Activity of Ru 3(CO) 12 is about 20 times higher than Mo(CO) 6 and W(CO) 6. The effect of process parameters on hydrogen production catalysed by Mo(CO) 6 was studied in some detail. Hydrogen production was found to increase with increasing KOH concentration. Also, hydrogen production increased with increasing Mo(CO) 6 concentration up to 0.04 M and then decreased. Hydrogen turnover number increased with increasing CO loading pressure in the range of 1–3.1 MPa, remained practically constant in the range of 3.1–4.1 MPa and decreased with increasing CO loading pressure from 4.1 to 6.2 MPa. The effect of CO on hydrogen production could be explained by a postulated mechanism involving equilibrium formation of formate ion which reacts with Mo(CO) 5 in a rate determining step to generate a metalloformate, Mo(CO) 5HCOO −. Hydrogen production increased with increasing solvent polarity. Solvent effect is attributed to the stabilization of charged intermediate species.