Support effects on the structure and performance of ruthenium catalysts for the Fischer–Tropsch synthesis

Abstract

The influence of support and metal precursor on Ru-based catalysts has been studied in the Fischer–Tropsch synthesis (FTS) combining flow reactor and quasi in situinfrared spectroscopy experiments. A series of supported ruthenium catalysts (3 wt.%) have been prepared using two different TiO2 (P25, 20% rutile and 80% anatase; Hombifine, 100% anatase) and SiO2·Al2O3 (28% Al2O3) as supports and RuCl3·nH2O as metal precursor. The catalysts were labeled as RuTi0.8, RuTi1 and RuSA respectively. Another catalyst (RuTi0.8N) has been synthesized with TiO2·P25 and Ru(NO)(NO3)3. After thermal treatments in air at 723 K and hydrogen at 443 K, ruthenium metal particles are agglomerated when pure anatase TiO2 and SiO2·Al2O3 are used as supports, leading to low active catalysts. In contrast, and despite the lower specific surface area of TiO2·P25 as compared to that of the other supports, well dispersed Ru particles are stabilized on titania P25. Remarkably, electronic microscopy studies demonstrate that Ru is deposited exclusively on the rutile phase of TiO2·P25. The catalytic performance shown by all these catalysts in FTS reactions follows the order: RuTi0.8 > RuTi0.8N > RuSA ≫ RuTi1. The same trend is observed during quasi in situ FTS experiments conducted in an infrared (IR) spectroscopy cell. The FTIR spectra of TiO2·P25 supported samples show that both samples behave similarly under the FTS reaction. This work shows that the structure of the support, rather than its specific surface area or the Ru precursor, is the parameter that determines the dispersion of Ru particles, hence their catalytic performance.