Catalysis of the water gas shift reaction by polymer-immobilized rhodium complexes

Abstract

Catalysts for the water gas shift prepared from RhCl 3·3H 2O immobilized on several porous aminated polymers in neutral aqueous and aqueous organic solvent media are described. Those using poly(4-vinylpyridine) as the support proved to be the most active among those surveyed, and the effects of varying different experimental parameters were investigated. The turnover frequencies for the production of H 2 displayed a nonlinear dependence on the partial pressure of CO in the 0–1.5 atm range but were independent of the polymer loading in the range 0.5 to 1.5 × 10 −4 mol RHCl 3H 2O/ g of polymer. An activation energy of 18.4 ± 0.9 kcal/mol was obtained from a linear Arrhenius plot based on H 2 production over the temperature range 80–110°C. The activity of the poly(4-vinylpyridine)-anchored catalyst was found to be insensitive to pH in the 3–5 zone but to fall off sharply outside this range. A catalysis mechanism consistent with the quantitative behavior is proposed. This species also catalyzes the Reppe-type transformations (hydrogenation and hydroformylation) of alkenes as well as the reduction of nitrobenzene to aniline.