Syngas conversion to ethanol by supported catalysts is an important progress in C, chemistry. It has been reported by our laboratory that Rh sites and niobia sites coexisted on Rh-Nb(2)O(5)/SiO(2) catalysts as detected by means of reaction chemistry 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(2)O(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 FUR spectra of the above mentioned catalysts were studied. The peak at 1740 cm(-1) (vw) may be assigned to that at 1560 cm(-1) (m, broad) to while that at 1269 cm-1 (s) most probably to a bridging species, [GRAPHICS] (3) The existence of Rh(0), Rh(1), Nb(v), Nb(IV) and two types of carbonoceous deposits on syngas treated Rh-Nb(2)O(5)/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 Rh ) 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) under bar to form coordinated ketene, and further hydrogenation to ethanol or aldehyde with simultaneous regeneration of the active site by hydrogenation and elimination of H(2)O(3) while r_ethane CH , was produced by hydrogenation of the coordinated carbene (CH(3)) under bar, in a secondary reaction pathway. The true nature of SMPI in the present system been discussed
