Infrared study of the adsorption of ethanoic acid, acrylic acid, acetone, acrolein and propene–NO mixtures on Rh/SiO2 catalysts

Abstract

Infrared spectra of the adsorbed products of reaction of propene and NO over Rh/SiO₂ are compared with spectra of adsorbed acetone, acrolein, acrylic acid and ethanoic acid. Acetone and acrolein formed hydrogen bonds with surface silanol groups and underwent decomposition on rhodium to give rhodium carbonyl species. The carboxylic acids also gave rhodium carbonyl species, but for ethanoic acid this only occurred at high temperature. Both acids were adsorbed on silica either through chemisorption giving a surface ester or as a weakly held dimer. Heat treatment of Rh/SiO₂ in propene/NO mixtures gave acrylic acid as the dominant partial oxidation product. However, addition of propene before NO to the reaction system led to the generation of a surface poison which inhibited the oxidation of propene.