Infrared study of the adsorption of acetone, acrolein, ethanoic acid and propene–NO mixtures on Rh/Al2O3 catalysts

Infrared spectra are reported of adsorbed products from exposure of Rh/Al2O3 at ca. 300 and 473 K to propene–NO mixtures, ethanoic acid, acetone and acrolein. Ethanoic acid was dissociatively adsorbed, giving ethanoate ions on alumina and a rhodium carbonyl species. The latter species was also formed from acrolein which was adsorbed on alumina in four ways: hydrogen bonding with hydroxyl groups, ligating to Al3+ sites and oxidation to acrylate or 2-formylethanoate anions. Acetone was associatively adsorbed via hydrogen bonding or coordinative interactions and was oxidised to ethanoate or methanoate anions on alumina. Carbonyl complexes were formed on rhodium. The oxidation of propene by NO over rhodium in Rh/Al2O3 catalysts specifically gave acrylate anions as the dominant adsorbed reaction product.