Cobalt-based Nanoreactors in Combined Fischer-Tropsch Synthesis and Hydroprocessing: Effects on Methane and CO2_{2} Selectivity

Fischer-Tropsch synthesis: Four types of bi-functional catalysts with cobalt nanoparticles supported on meso- or microporous silicates or aluminosilicates are investigated regarding the obtained CO$_{2}$ and CH$_{4l}$ selectivity under low-temperature Fischer-Tropsch reaction conditions. In situ x-ray absorption spectroscopy results under industrially relevant conditions reveal that strong cobalt-support interactions and oxidized cobalt species are the main factors determining the selectivity depending on the specific support material used. The production of liquid hydrocarbons from syngas (CO and H$_{2}$) via the combined Fischer-Tropsch (FT) synthesis and hydroprocessing (HP) is a promising strategy to provide valuable chemicals and fuels based on renewable feedstocks. High yields of liquid products are essential for industrial implementation since short-chain side products like methane and CO$_{2}$ reduce the overall carbon efficiency, which holds true especially for bi-functional Co/zeolite catalysts. In order to investigate the influence of the support material properties on the methane and CO$_{2}$ selectivities in the combined FT and HP reaction, we synthesized four well-defined catalyst materials with similar cobalt particle sizes. The active material is supported on either meso- or microporous silicates or aluminosilicates. The catalytic properties are investigated in FT experiments at industrially relevant conditions (20 bar, 200–260 °C) and correlated with in situ x-ray absorption spectroscopy results to determine the chemical environment responsible for the selectivity observed. The origin of the high methane selectivity detected for crystalline and amorphous aluminosilicate was mainly traced back to the strong cobalt-support interactions. The high CO$_{2}$ selectivity, observed only for crystalline zeolite materials, is driven by the presence of oxidized cobalt species, while the acidic support in combination with micropores and possible overcracking leads to the observed drop in the C$_{5+}$ selectivity

Au,@ZrO₂ yolk-shell catalysts for CO oxidation: Study of particle size effect by ex-post size control of Au cores

Gold nanoparticles supported on transition metal oxides are found to exhibit a pronounced particle size effect in CO oxidation. However, the preparation of comparable supported gold nanoparticles with different sizes remains challenging, since the catalytic behavior of these materials is very sensitive to the preparation conditions. To overcome this difficulty, Au, @ZrO2 catalysts with gold core sizes between 5 and 15 nm were prepared by partial leaching of gold in an ex-post manner. The material obtained offers a unique comparability for particle size effect studies in CO oxidation. No effect of gold particle size was observed in the studied size range. (C) 2012 Elsevier Inc. All rights reserve

Influence of the Microstructure of Gold-Zirconia Yolk-Shell Catalysts on the CO Oxidation Activity

The gold−zirconia yolk−shell system is an interesting catalyst for CO oxidation. The size distribution of the gold nanoparticles is very narrow, and they are well separated from each other also after treatment at high temperature, which is due to their encapsulation in crystalline zirconia hollow spheres. Because this allows thermal and chemical treatment without affecting the size distribution, different defect structures of the gold nanoparticles can be induced, and the effect on catalytic activity can be investigated. Line profile analysis of the powder diffraction data based on the whole powder pattern modeling approach was used to determine the domain size distribution and lattice defects present in this two-phase system. The influence of different diffractometer setups on the results of the line profile analysis was also investigated. Variation of the chemical and thermal treatment procedures allowed altering the microstructure of the system. The resulting catalysts showed substantial variation in the activity for CO oxidation. Lower dislocation densities and less stacking faults result in decreased catalytic activity. These contributions to activity could be studied without any superimposed size effect due to the constant gold particle sizes