Catalytic Reactions under Unsteady-State Conditions. Modelling with COMSOL

National audienc

Effect of calcination temperature on the size of cobalt nanoparticles and catalytic performance of cobalt alumina-supported Fischer Tropsch catalysts

International audienc

Impact of aqueous impregnation on the long-range ordering and mesoporous structure of cobalt containing MCM-41 and SBA-15 materials

International audienceThe effect of modification with cobalt via aqueous impregnation on the structure of MCM-41 and SBA-15 materials was studied using X-ray diffraction (XRD) at low scattering angles and low-temperature nitrogen adsorption. It was shown that the introduction of small amounts of cobalt resulted in dramatic changes in the structure of MCM-41 silica. The low angle XRD peaks characteristic of long-range ordering disappeared while the BET surface area and the total pore volume decreased considerably. Only micropores smaller than 20 Å were detected in the cobalt containing MCM-41 materials. A much smaller impact of impregnation with cobalt on the hexagonal structure and porosity was observed for SBA-15 materials. The periodic structure, surface area and total pore volume of SBA-15 mesoporous silica remained almost unchanged on impregnation with cobalt nitrate, catalyst drying and calcination. Low angle XRD patterns typical of hexagonal structure were still well resolved and intense in the SBA-15 materials containing up to 20 wt. % of cobalt. Analysis of XRD intensities suggested that after aqueous impregnation and drying a considerable amount of cobalt ions was located in the SBA-15 mesopores. Nitrogen adsorption-desorption data indicated plugging a part of SBA-15 mesopores in cobalt containing samples. Due to the high stability, SBA-15 silica appears to have a good potential for its use as a support for metal and oxide catalysts

Reducibility of Cobalt Species in Silica-Supported Fischer–Tropsch Catalysts

International audienceReducibility of Cospecies in silica supported Fischer–Tropsch catalysts was studied using in situ XRD,in situ EXAFS,andFTIR spectroscopy with carbon monoxide as a molecularprobe. Crys- talline Co phases in the oxidised catalysts were characterised using XRD. In the oxidised samples with a large concentration of amor- phousphase, EXAFS showed the presence of small oxide clusters including several Co atoms.It was found (insituXRD,EXAFS)that calcination of oxidised Co catalysts under inert atmosphereresulted in a selective transformation of Co3O4 to CoO at 623–673K. FTIR spectroscopy with CO as a molecular probe revealed the presence of different sites associated with Co after the reduction of the catalysts withhydrogenat723K:Cometalsites(νCO =2025cm− 1 ), Co2+ions in the crystalline phase of CoO (νCO =2143cm−1) , and Co n+ species intheamorphous phase(νCO=2181cm− 1 ). The results (XRD, EXAFS, FTIR)showed that the hydrogen reduction properties of particles of cobalt oxide on silica depended on the size of the Co3O4 crystallites. The ease of reduction to metal species decreased from larger(200–700 ̊A)tosmaller(60 ̊A)particles.