Fischer-Tropsch synthesis: Osmium promoted Co@HCS catalysts

Abstract

Little attention has been given to the use of osmium as a promoter for Fischer-Tropsch Synthesis (FTS). In previous studies, Os has proven to be a poor FT catalyst, but its use as a catalyst promoter has not been studied. In this study, the synthesis and use of Os nanoparticles supported on/in Co@HCS (HCS = hollow carbon sphere) FT catalysts are reported. The hollow morphology of the HCSs was exploited to study the influence of Os promoter nanoparticle location relative to the Co3O4 nanoparticles (dCo = 3.5–12.5 nm) and on the effect of Os on the reduction behaviour and activity of the Co FT catalyst. Os (0.1, 0.5 and 1 wt%) nanoparticles were loaded both inside and outside the HCSs, while the Co3O4 particles (Co 10 wt%) were loaded inside of the HCSs to give CoOs@HCS and Os/(Co@HCS). Electron microscopy, in situ PXRD, PDF, TGA, BET, and TPR studies revealed that both catalysts were successfully synthesized. The use of ex-situ PXRD, PDF and TPR studies provided information on the Co phases and reduction pathways of the Co3O4 metal catalyst and the spillover effect from Os to Co. Co3O4 and CoO phases were observed for the CoOs@HCS and Os/(Co@HCS) catalysts. More interesting was the observation of the Co fcc phase in the OsCo@HCS catalysts, indicating the importance of the Os-Co interaction. The catalyst with Co and Os close together (primary spillover process) gave a higher Fischer-Tropsch activity (38.5–46.4 × 10−6 molCO/gCo.s) and higher C5+ production than both the unpromoted catalyst (27.8 × 10−6 molCO/gCo.s), and the catalysts where Os and Co were separated (25.1–36.4 × 10−6 molCO/gCo.s) by the mesoporous carbon shell (secondary spillover effect). The studies on both CoOs@HCS and Co/(Os@HCS) catalysts have indicated for the first time the effect of Os on Co catalysts, with particular reference to FTS.