FTIR STUDIES OF CO CHEMISORPTION AND REACTIVITY ON RH/SIO2 CATALYSTS PROMOTED BY NIOBIUM OXIDE

(Rh + Nb)/SiO2 catalysts were obtained by anchoring of nanometer size Rh particles on surface low-valent Nb(n+) ions. These materials exhibit the following specific features compared to Rh/SiO2: a low Rh surface coverage by chemisorbed hydrogen and carbon oxide; a high-frequency shift of linear CO absorption band and appearance of two absorption bands of a C- and 0-bonded CO at 1704 and 1652 cm-1. On exposure to H-2, the stability of surface carbonyls increases in the sequence: Rh-CO-Nb(n+) <Rh-CO less-than-or-equal-to Rh2 (CO) < Rh + (CO)2. The possible role of C- and 0-bonded CO complexes in the conversion of syngas on supported rhodium catalysts promoted by transition element oxides is discussed.