Effect of Ru-promotion on the catalytic performance of a cobalt-based Fischer-Tropsch catalyst activated in syngas or H2

Abstract

This research demonstrated the effect of Ru addition on the structure-performance relationships of Co/SiO2 catalysts reduced in either syngas or H2. The activity results show that the syngas reduced Co-Ru/SiO2 catalyst afforded better product selectivity (high C5+ = 86.8% and low CH4 = 8.45%) but low activity (CO conversion = 15.2%) compared to the H2 reduced Co-Ru/SiO2 catalyst (C5+ = 78.9%, CH4 = 10.5%, CO conversion = 44.8%) at 120 h TOS. Furthermore, the activity of the unpromoted H2-reduced Co/SiO2 catalyst (C5+ = 82%, CH4 = 9.19%, CO conversion = 25%) was comparable to that of syngas catalyst Co-Ru/SiO2 catalyst. Ru improved the reducibility and subsequent dispersion of the Co sites leading to enhanced catalytic activity for the catalyst reduced by H2-reduction. However, the addition of Ru suppressed the CO hydrogenation for the syngas reduced Co-Ru/SiO2 catalyst. This strongly reflects on the superiority of H2 as a reducing agent for Ru-promoted Co-based catalysts. XRD and XPS analysis of the spent catalysts points out at the formation of Co2C species, which suppressed the FT activity and stimulated the formation of olefinic products over the syngas-reduced catalysts. While there is a potential for syngas reduction for unpromoted Co-based catalysts, in small FTS plants, this system in not favorable for Ru-promoted catalysts.