HYDROGEN ACTIVATION BY SOLUBLE METAL-OXIDE COMPLEXES

To better define the chemistry associated with nucleophilic oxide centers, the catalysis of the water-gas shift reaction was investigated in triethylene glycol solution (150-250-degrees-C and 1-300 atm) by employing alkali metal hydroxide catalysts. Under reaction conditions most of the sodium salt is in the form of the formate complex, which is produced through the carbonylation of hydroxide ion. The resultant water-gas shift reaction is first order in sodium formate over a concentration range from 0.01 to 1.0 M. Both formic and acetic acids have a beneficial effect on the rate of dihydrogen evolution within the sodium hydroxide-formate water-gas shift system. Deuterium, D2, is produced in 93% isotopic purity when the reaction is conducted in D2O-triethylene glycol-d2. it exhibits a substantial inverse kinetic isotope effect (k(H)/k(D) = 0.5) compared to the analogous water-gas shift reaction conducted in H2O-triethylene glycol. The kinetic results indicate that the sodium hydroxide-formate water-gas shift system proceeds through an intermediate (or transition state) with substantial H-H bond order. This activity contrasts with earlier proposals for nucleophilic dihydrogen activation, which focused on a free hydride ion intermediate.