CO hydrogenation over RhVO4/SiO2, Rh/V2O3 and Rh/SiO2 catalysts:: reduction and regeneration of RhVO4

The CO hydrogenation over a RhVO4 catalyst on an SiO2 support (RhVO4/SiO2) has been investigated after H-2 reduction at 300degreesC, and the results are compared with those of Rh/V2O3 and unpromoted Rh/SiO2 catalysts. The RhVO4 compound was formed on the SiO2 support by calcination in air at 700degreesC with the atomic ratio of V/Rh = 1. The RhVO4 was decomposed to Rh metal particles (3.0 nm) and V2O3 particles (highly dispersed) by the H-2 reduction, where a strong metal-oxide (Rh-vanadia) interaction (SMOI) was induced. The RhVO4/SiO2 catalyst after the H-2 reduction exhibited higher activity in CO hydrogenation, compared with the other Rh catalysts. The selectivity to C-2 oxygenates of the RhVO4/SiO2 and RhN2O3 catalysts was higher than that of the unpromoted Rh/SiO2 catalyst, although the selectivity decreased with increasing CO conversion. The RhVO4 was also formed on the SiO2 surface by calcination in air even at 500degreesC, although the XRD study suggested that the formation was less perfect. After H-2 reduction at 300 degreesC, the catalytic activity of the catalyst calcined at 700 degreesC was higher than that of the one calcined at 500 degreesC, indicating a stronger Rh-vanadia interaction in the former catalyst. The RhVO4 can be regenerated by calcination in O-2 at 700 degreesC after an intentional sintering treatment (at 700 degreesC in He) of the RhVO4/SiO2 catalyst, and hence, the activity and the selectivity to C-2 oxygenates were restored. (C) 2002 Elsevier Science B.V. All rights reserved.