The effects of the nature of TiO2 supports on the catalytic performance of Rh–Mn/TiO2 catalysts in the synthesis of C2 oxygenates from syngas

Abstract

The effects of TiO2 phase composition on the catalytic and physico-chemical properties of supported Rh catalysts in the synthesis of C2 oxygenates from syngas were studied. The catalysts supported on anatase containing TiO2 were more active than those supported on rutile containing TiO2. Meanwhile, the catalyst supported on pure rutile TiO2 exhibited a greatly higher C2 oxygenate selectivity than that supported on anatase TiO2, and the TiO2 with mixed phase composition could further improve the C2 oxygenate selectivity compared with the pure phase TiO2. The results showed that the higher Rh dispersion and CO adsorption capacity at the reaction temperature were obtained on the anatase/anatase-rich TiO2 supported Rh catalysts, resulting in their higher CO conversion compared with catalysts supported on rutile/rutile-rich TiO2. The chemical states of Rh sites can be affected by the different electron-donor properties of TiO2 with different crystalline phases. The electropositivity of Rh+ sites was weakened when using the rutile containing TiO2 supports, which is conducive to transformation of Rh+(CO)2 into Rh–CO species and weakens the Rh–CO bond strength, finally resulting in the increased CO insertion reaction, and accordingly the increase of C2 oxygenate selectivity over the rutile containing catalysts. Moreover, the remarkably higher TOF of RM/TiO2-Ar can be attributed to the higher CO adsorption capacity and fast transformation of Rh+(CO)2 into Rh–CO species.