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

The CO hydrogenation over a RhVO4 catalyst on an SiO2 support (RhVO4/SiO2) has been investigated after H2 reduction at 300 °C, 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 700 °C 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 H2 reduction, where a strong metal–oxide (Rh–vanadia) interaction (SMOI) was induced. The RhVO4/SiO2 catalyst after the H2 reduction exhibited higher activity in CO hydrogenation, compared with the other Rh catalysts. The selectivity to C2 oxygenates of the RhVO4/SiO2 and Rh/V2O3 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 500 °C, although the XRD study suggested that the formation was less perfect. After H2 reduction at 300 °C, the catalytic activity of the catalyst calcined at 700 °C was higher than that of the one calcined at 500 °C, indicating a stronger Rh–vanadia interaction in the former catalyst. The RhVO4 can be regenerated by calcination in O2 at 700 °C after an intentional sintering treatment (at 700 °C in He) of the RhVO4/SiO2 catalyst, and hence, the activity and the selectivity to C2 oxygenates were restored.