Jae Min Cho

Fischer–Tropsch synthesis on Co/AlSBA-15: effects of hydrophilicity of supports on cobalt dispersion and product distributions

The surface properties of Al-incorporated ordered mesoporous SBA-15 (AlSBA-15) containing 25 wt% cobalt were studied for Fischer–Tropsch synthesis (FTS) reaction to verify the effects of hydrophilicity of the AlSBA-15 surfaces on the cobalt distribution and the product distribution, especially for C2–C4 hydrocarbons according to the contents of aluminum on the SBA-15. The AlSBA-15 was synthesized by varying the amount of Al2O3 in SBA-15 from 0.2 to 0.4 wt% during one-pot hydrothermal synthesis. The selectivity of C2–C4 hydrocarbons was increased with the increase in aluminum contents on the SBA-15 by showing higher olefin selectivity. The increased C2–C4 selectivity at similar CO conversions was mainly attributed to the formation of small cobalt particles with higher oxidation state, stronger metal–support interaction and less aggregation of particles on the outer surfaces of the AlSBA-15, which suppressed the secondary reactions of the olefins to heavy hydrocarbons in the regular mesopores of the acidic sites of the AlSBA-15. To understand the surface properties of Co/AlSBA-15 catalysts, the distribution and reduction behaviors of cobalt particles and the surface hydrophilicity (relative amounts of surface hydroxyl groups) of the Al-incorporated SBA-15 were characterized in terms of aluminum concentrations in the ordered mesoporous SBA-15.

Thermally Stabilized Cobalt-Based Fischer–Tropsch Catalysts by Phosphorous Modification of Al2O3: Effect of Calcination Temperatures on Catalyst Stability

A phosphorous‐modified Al2O3 support was prepared by the impregnation method and applied for the preparation of cobalt‐based Fischer–Tropsch synthesis (FTS) catalysts (Co/P–Al2O3), which were calcined at different temperatures. The Co/P–Al2O3 showed a significant increase of thermal stability with a higher catalytic performance without severe deactivation even above a calcination temperature of 600 °C compared with the unmodified Co/Al2O3. These findings are explained by the suppressed cobalt aluminate formation and less pronounced aggregation of cobalt particles. The suppressed aggregation of cobalt particles is attributed to the localized presence of aluminum phosphate by forming a thermally stable metal–phosphorous oxo‐species on Al2O3 surfaces thus suppressing the migration of cobalt particles to the outer pore mouths of the support. These effects significantly enhance the catalytic activity with a higher thermal stability of the catalysts.

Fischer-Trospch Synthesis on Ordered Mesoporous Cobalt-Based Catalysts with Compact Multichannel Fixed-Bed Reactor Application: A Review

CO hydrogenation to hydrocarbons through Fischer–Tropsch synthesis (FTS) reaction is one of the promising chemical processes, which can convert alternative feedstocks such as natural gas or biomass into synthetic fuels. The FTS reaction has received many attentions due to a limited petroleum resource with an increased demand for using alternative carbon sources such as stranded gas or shale gas. Some proper synthetic methods of an effective FTS catalyst having a larger active metal surface area and a lower deactivation rate are the most important issues for a long-term operation. Therefore, some ordered mesoporous materials (OMM) have been widely investigated in the field of CO hydrogenation using some heterogeneous catalysts. The present brief review paper summarized the various preparation methods of the ordered mesoporous materials for the possible applications of FTS reaction with a lower deactivation rate and a higher catalytic performance. The applications of the ordered mesoporous cobalt oxides for FTS reaction are briefly introduced and the ways to improve a structural stability even under reductive CO hydrogenation conditions by using efficient pillaring materials as well as by preparing mixed metal oxides. A higher catalytic activity of the ordered mesoporous cobalt oxide was also verified in a multi-channel fixed-bed compact reactor having the intersected interlayers of micro-channel heat exchanger. The thermal stability of ordered mesoporous cobalt-based catalysts was mainly affected by a structural stability which can easily remove the heavy hydrocarbons from the inner surfaces.

Effect of Mn promoter on Rh/tungsten carbide on product distributions of alcohols and hydrocarbons by CO hydrogenation

Roles of Mn promoter on Rh-impregnated mesoporous tungsten carbides (WxC) have been investigated for direct synthesis of mixed alcohols by CO hydrogenation of syngas. Mn/Rh ratio on the mesoporous WxC, prepared using a hard-template of mesoporous SBA-15, significantly altered CO conversion and product distributions. An optimal Mn content of 3 wt% on Rh/WxC was responsible for a high CO conversion of 8.1% and selectivity for higher alcohols of 54.4% compared with other catalysts. The enhanced activity and selectivity towards alcohols at an optimal Mn content were mainly attributed to close interaction of Rh and Mn nanoparticles with partially reduced Rh nanoparticles on the WxC, which enhanced CO adsorption as well as suppressed CO hydrogenation to produce light hydrocarbons. This superior activity originated from a higher dispersion of Rh nanoparticles, which intimately interacted with Mn species, maintaining an appropriate surface ratio of metallic Rh to oxidized Rh+ surfaces. The structures of the ordered mesoporous WxC support greatly altered the chemical states of Rh nanoparticles by generating a strong metal–support interaction as well, and Rh–Mn(3)/WxC showed a high production rate of higher alcohols by synergistic effects of the supported Rh–Mn nanoparticles with an appropriate interaction with the mesoporous WxC support.