The extent of Rh-niobia interaction in niobia-supported Rh (Rh/Nb2O5), niobia-promoted Rh/SiO2 (Nb2O5-Rh/SiO2) and RhNbO4/SiO2 catalyst after H-2 reduction has been investigated by H-2 and CO chemisorption measurements. These catalysts have been applied to selective CO oxidation in Hz (CO+H-2+O-2) and CO hydrogenation (CO+H-2), and the results are compared with those of unpromoted Rh/SiO2 catalysts. It has been found that niobia (NbOx) increases the activity and selectivity for both the reactions. (C)2000 Elsevier Science B.V. All rights reserved.