Effects of Co and Ru Intimacy in Fischer-Tropsch Catalysts Using Hollow Carbon Sphere Supports: Assessment of the Hydrogen Spillover Processes

Mesoporous hollow carbon spheres (MRCSs) were synthesized (d = 290 nm; carbon shell 20-35 nm), and their hollow morphology was exploited to study the influence of Ru nanoparticle location relative to Co3O4 nanoparticles on the reduction behavior and activity of Co Fischer-Tropsch catalysts. Ru nanoparticles were loaded both inside and outside the MHCS, while Co3O4 particles (ca. Co 15 wt % loading) were loaded on the outside of the MHCS. The use of in situ powder X-ray diffraction (PXRD) and temperature-programmed reduction studies on the catalysts indicated the effect of Ru location on the Co3O4 reduction pathways. A secondary hydrogen spillover effect was invoked to explain a complete reduction of the Co3O4 on Ru@MHCS@Co at 450 degrees C. Secondary hydrogen spillover enhanced the CoO to Co transformation by lowering the reduction temperature when compared to the unpromoted catalyst. Primary hydrogen spillover was inferred to explain the complete reduction of Co3O4 to Co metal on CoRu/MHCS at 300 degrees C. After catalyst activation at 350 degrees C, the primary spillover process yielded a catalyst with higher Fischer-Tropsch activity (ca. 2X) than the unpromoted catalyst and the catalysts where Ru and Co were separated by the mesoporous carbon shell. This was partially related to the Co phases that formed on the carbon support during reduction and the catalyst degree of reduction that was reliant on the type of hydrogen spillover process.