Infrared study of CO chemisorption on zeolite and alumina supported rhodium

Abstract

The chemisorption properties of supported rhodium with respect to carbon monoxide are investigated by infrared spectrometry. Zeolite and alumina supported rhodium is obtained following hydrogen reduction. Highly dispersed rhodium is prepared on the zeolite support whatever the temperature of reduction over the range 200–600°C. For rhodium supported on alumina, the dispersion is less good and decreases when the conditions of reduction become more drastic. For particles of larger diameter than 20 Å, chemisorption of CO leads mainly to gem dicarbonyl species, the site of adsorption being one rhodium atom in the oxidized state. These gem dicarbonyl complexes are not formed at low temperature, but develop on warming up to room temperature. Dissociation of carbon monoxide is then assumed, CO in excess adsorbs on the surface Rh–O species to give gem dicarbonyl complexes, probably of Rh^I, which interact with the lattice in the case of zeolite support.