Effect of foreign ion additives on ceria surface reactivity towards isopropanol adsorption and decomposition: An infrared investigation

Infrared spectroscopy was employed to investigate reactions of isopropanol vapour on pure and doped ceria catalysts. The results obtained reveal that isopropanol is irreversibly adsorbed (at 298 K) on strongly dehydroxylated pure ceria surfaces in the form of coordinated molecules and, probably, two different types of isopropoxide ions (terminal and bridge-bonded). The coordinated molecules are suggested to be of importance in the alcohol dehydration (at > / 573 K) to give propene, whereas the bridging isopropoxides to be the surface intermediate of the dehydrogenation (at > /423 K) to give acetone. At > 573 K, the acetone takes part in a surface-mediated bimolecular reaction to produce isobutene and methane, and acetate surface species. The dehydration and dehydrogenation activities of ceria are seen to reside at eus Ce⁴⁺-²⁻ pair sites. The secondary reaction of acetone, however, is suggested to occur on Ce⁴⁺-OH⁻ surface sites. Doping of ceria with Na⁺ ions suppresses alcohol dehydration as well as further reactions of acetone. Cr³⁺- and Al³⁺-doping improve the surface selectivity towards dehydrogenation and dehydration reactions respectively.