Abstract: Syngas conversion to ethanol by supported catalysts is an important progress in C_1 chemistry. It has been reported by our laboratory that Rh sites and niobia sites coexisted on Rh-Nb_2O_5/SiO_2 catalysts as detected by means of reaction chemi- stry involving the catalytic aromatization and polymerization of acetylene on such catalysts. This paper reports a further study consisting of the following three parts: (1)The probable existence of Nb-H bonds on hydrogen-reduced Rh-Nb_2O_5/ SiO_2 was deduced from the catalytic activity toward polymerization of acetylene to polyacetylene and the loss of catalytic activity toward cyclotrimerization of acetylene of such catalysts. (2) The FTIR spectra of the above mentioned catalysts were studied. The peak at 1740 cm~(-1) (vw) may be assigned to v_(Ph-H), that at 1560 cm~(-1) (m, broad) to v_(Nh-H), while that at 1269 cm~(-1) (s) most probably to a bridging species, Rh—H—Nb. (3) The existence of Ph~0, Rh~Ⅰ, Nb~Ⅴ, Nb~Ⅳ and two types of carboneceous deposits on syngas treated Rh-Nb_2O5/SiO_2 catalysts was detected by XPS; A model of active center, A (cf. Fig.3) (abbr. B), formed by partial reduction of niobia through hydrogen spillover and “wetting” or partial coating of the surfaces of rhodium particles (Rh_x~0Rh_y~I) by the partially reduced niobia, has been proposed. By analogy with known organometallic chemistry, the major reaction pathway might involve migratory insertion of chemisorbed species C to form E, hydrogenation to F cis-coupling with CO to form coordinated ketene, and further hydrogenation to ethanol or aldehyde with simultaneous regeneration of the active site by hydrogenation and elimination of H_2O; while methane CH_4 was produced by hydrogenation of the coordinated carbene CH_2 in a secondary reaction pathway. The true nature of SMPI in the present system has also been discussed.