Homogeneous water-gas shift reaction

Mechanistic Aspects of the Homogeneous Water Gas Shift Reaction... 

It now appears that at least two mechanisms exist for the base-promoted homogeneous water gas shift reaction, differing in the method of hydride formation. The "associative mechanism", first proposed by Pettit and co-workers (1,4), involves nucleophilic attack on a carbonyl ligand and it has two variations. 

Base-catalyzed homogeneous water-gas shift reaction... 

Pettit and coworkers—metal hydride intermediates by weak base attack over Fe carbonyl catalysts. Pettit et al.ls approached the use of metal carbonyl catalysts for the homogeneous water-gas shift reaction from the standpoint of hydroformyla-tion by the Reppe modification.7 In the typical hydroformylation reaction, an alkene is converted to the next higher aldehyde or alcohol through reaction of CO and H2 with the use of a cobalt or rhodium carbonyl catalyst. However, in the Reppe modification, the reduction is carried out with CO and H20 in lieu of H2 (Scheme 6) ... 

Fachinetti and coworkers—acid cocatalyzed water-gas shift over Rh and Ru carbonyl catalysts. Fachinetti and coworkers133 145 published research on the acid cocatalyzed homogeneous water-gas shift reaction by Rh4(CO)12 and Ru3(CO)12 precursors in aqueous pyridine solution. For Rh carbonyl, experiments were carried out at 80 °C, PCo = 1 atm, and [Rh] = 0.02 mol/L in a solution of pyridine containing 3% H20. They observed the following reaction in anhydrous pyridine ... 

Rice, S.F., Steeper, R. R. Aiken, J. D. Water Density Effects on Homogeneous Water-Gas Shift Reaction Kinetics J. Phys. Chem. A, 102(16) (1998), 2673-2678. 

The main byproduct forming reactions in the BASF and Monsanto processes are different. In the former it is the liquid phase Fischer-Tropsch-type reaction, that leads to the formation of products such as such as alkyl acetates, methane etc. In the Monsanto process it is the homogeneous water-gas shift reaction that produces C02 and H2 as byproducts. Also note that the Monsanto process is superior in terms of selectivity, metal usage and operating conditions. 

DBU is an effective cocatalyst for the homogeneous water gas shift reaction catalyzed by Ru3(CO),2 or by Os3(CO),2 under basic conditions (83CL1837 85NKK503). 

At a stoichiometric ratio, the conversion rate to the right-hand side is maximal for high temperatures and relatively low pressures. However, excess steam of 300 % away from the stoichiometric mixture is generally injected to move the equilibrium towards more CO2 in the homogeneous water-gas shift reaction... 

D. J. Cole-Hamilton, Photocatalysis of the homogeneous water-gas shift reaction, J. Chem. Soc. Chem. Commun. (24) (1980) 1213-1215. 

Studies on the uncatalyzed water-gas-shift reaction are most likely influenced by the surface-catalyzed reactions [47]. The experiments reported here were carried out in a reactor seasoned (or aged ) under reaction conditions [116]. The relatively low reaction rate of the methanol oxidation in SCW compared to other studies and the relatively high ignition temperature leads to the assumption that the catalytic activity of the surface was relative low [124], probably because the surface is covered by an oxide layer. This also means that the catalytic activity concerning the surface-catalyzed water-gas-shift reaction is low. And this leads to the assumption that the homogeneous water-gas-shift reaction - as mentioned above - is of major importance and should be considered in models for SCWO. 

Rice, S. F., Steeper, R.R. and Aiken, J.D. (1998) Water density effects on homogeneous water-gas shift reaction kinetics, J. Phys. Chem. A 102,2673-2678... 

Enick, R., Bustamante, F., lyoha, O., Howard, B., Killmeyer, R., Morreale, B., et al. (2004). Conducting the homogenous water-gas shift reaction in a palladium-copper alloy membrane reactor at high temperature and pressure. NETL report. 

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