Activity Of Co-based Catalysts Research Articles

Effect of start-up solvent on the performance of Co catalyst for Fischer-Tropsch synthesis in stirred-tank reactor

The starting solvent is essential for carrying out Fischer-Tropsch (FT) synthesis in a stirred-tank reactor. The most commonly used solvents are C28+ hydrocarbon oils, wax, heavier wax, and FT wax. In general, FT activity of Co-based catalysts was found to decrease for initial days, and one of the reasons may be related to the filling of catalyst pores with heavier wax leading to lower gas diffusions and thus lower CO conversion. In this work, therefore, solvents with varying molecular weight and polarity, including glycerol, 1-octanol, Polywax-655, and dimethyl phthalate were tested as a starting medium for 0.27%Ag-25%Co/Al2O3 catalyst. It was found that low molecular weight non-polar solvent, for example, Polywax 655 showed higher conversions. On the other hand, glycerol a high polar solvent tends to firmly bound with a catalyst surface and the associated water produced during FT synthesis could trigger catalyst deactivation from the oxidation of cobalt. This indicates the superiority of non-polar over polar solvents for FT synthesis. However, 1-octanol as a starting solvent showed the least catalytic deactivation rate and competitive FTS activity. Thus, 1-octanol has the potential as a start-up solvent for FT reaction in stirred tank reactors.

Effects of mesoporous structure and Pt promoter on the activity of Co-based catalysts in low-temperature CO2 hydrogenation for higher alcohol synthesis

Mesoporous Co3O4 (Co3O4-m) was synthesized with mesoporous silica (KIT-6) as a hard template. Co3O4-m was characterized by in situ reduction XRD, BET, TEM, and H2 TPR. The partly reduced Co3O4-m was studied as a catalyst for higher alcohol synthesis from CO2 hydrogenation. The metallic Co reduced from Co3O4 was the main activity site for the CO2 hydrogenation. The ordered mesoporous structure of the Co3O4-m catalyst promotes the growth of carbon chains for the production of higher hydrocarbons and alcohols and reduces the selectivity for CH4 from that of the partially reduced Co3O4 nanoparticles. The highest yield of higher alcohols was obtained in 1.6 mmol gcat−1 h−1 at 200 °C over the Co3O4-m catalyst, which was reduced at 300 °C. In addition, the selectivity for CH4 further decreased at 200 °C over the Pt/Co3O4-m catalyst, while the selectivity for CO and alcohols increased, owing to the reverse water gas shift ability of Pt. However, the conversion of CO2 significantly decreased. The yield of higher alcohols (1.5 mmol gcat−1 h−1) was slightly lower than that of Co3O4-m catalysts under the same reaction conditions.

A study on physico-chemical properties and activity of Co-based catalysts supported on SBA-15 in the Fischer-Tropsch synthesis

Cobalt catalysts supported on SBA–15 and SBA–15, modified by trimethylbenzene (TMB) were prepared from cobalt nitrate and cobalt acetate. Physico–chemical characteristics and activity of the obtained catalysts in Fischer–Tropsch Synthesis at 0.7 MPa were investigated. The results indicate that the use of TMB led to a widening the pores of SBA–15, improving the dispersity of cobalt oxide particles and enhancing the catalysts' reducibility and increasing the efficiency in liquid hydrocarbons' formation. Catalysts prepared from cobalt acetate, due to the formation of poorly reducible cobalt silicate and the abundance of acidic centres, expressed a lower activity compared to the catalysts prepared from cobalt nitrate. Ruthenium additives weakened interaction between cobalt and the carrier, improved catalysts' reducibility and the yield of hydrocarbons C5+ increased. The catalyst of 15 wt.% Co + 0.05 wt.% Ru supported on modified SBA–15 expressed a high efficiency in conversion of CO with the hydrocarbons' yield ∼50%.

Promotional Effect of Noble Metal to Co-based Fischer-Tropsch Catalysts Prepared from Mixed Cobalt Salts

Abstract Addition of very small amount of Ru, Pt and Pd exhibited great effect on the Co-based catalysts prepared by mixing impregnation of cobalt (II) nitrate and cobalt (II) acetate. Added small amount of Ru to this kind of catalyst showed extremely high activity, while no apparent CH4 selectivity change was observed. However, added Pt and Pd hardly exerted effect on the activity of Co-based catalyst, but increased CH4 selectivity remarkably.