For Fischer-Tropsch Synthesis Reaction Research Articles

Preparation of a novel structured catalyst based on aligned carbon nanotube arrays for a microchannel Fischer-Tropsch synthesis reactor

A novel microstructured catalyst based on aligned multiwall carbon nanotube arrays was synthesized and tested for Fischer-Tropsch synthesis (FTS) reaction in a microchannel reactor. Fabrication of such a structured catalyst first involved metal organic chemical vapor deposition (MOCVD) of a dense Al 2O 3 thin film over FeCrAlY foam to enhance the adhesion between ceramic-based catalyst and metal substrate. Aligned multiwall carbon nanotubes were deposited uniformly over the substrate by controlled catalytic decomposition of ethylene. These nanotube bundles were directly attached to FeCrAlY foam through a submicron layer of oxide thin film. Coating the outer surfaces of these nanobundles with an active catalyst layer forms a unique hierarchical structure with fine interstitials between the carbon nanotube bundles. The microstuctural catalyst possessed superior thermal conductivity inherent from carbon nanotube, which allows efficient heat removal from catalytic active sites during exothermic FTS reaction. The concept was tested and demonstrated in a microchannel fixed bed FTS reactor. FTS turn-over activity was found to enhance by a factor of four owing to potential improvement in mass transfer in the unique microstructure. Furthermore, improved temperature control with the carbon nanotube arrays also allows the Fischer-Tropsch synthesis being operated at temperatures as high as 265 °C without reaction runaway.

Structure and Fischer–Tropsch performance of iron–manganese catalyst incorporated with SiO 2

A systematic study has been carried out to investigate the impacts of SiO 2 content, incorporation manner of SiO 2 and drying process on the physico-chemical and catalytic performances of a precipitated iron–manganese catalyst for Fischer–Tropsch synthesis (FTS) in a fixed bed reactor (H 2/CO = 2.0, T = 265 °C, P = 2.5 MPa and GHSV = 1000 h −1). Characterization technologies of N 2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) were used to study the textural properties, bulk phase composition, reduction behavior and morphologies of the catalysts, and the SiO 2 framework in the catalysts. The results of characterization showed that the incorporation of SiO 2 leads to the increase in surface area. The catalyst with incorporated with precipitated SiO 2 has the highest surface area and exhibits a stronger interaction between iron and SiO 2 matrix than the interaction with binder SiO 2. The strong Fe–SiO 2 interaction restrains the reduction in H 2 and the carburization in syngas of the catalysts. The addition of both binder and precipitated SiO 2 greatly influences the activity and selectivity of FTS, and obviously improves its stability. For the FTS reaction tests, it was found that the catalyst activity is decreased with the increase of the amount of SiO 2 incorporated. For the catalysts incorporated with the same levels of SiO 2, the spray-dried catalyst has lower activity than the normal dried one. In addition, the catalyst incorporated with precipitated SiO 2 has higher activity than that with binder SiO 2. The FTS stability of the catalysts is improved with the incorporation of SiO 2. The selectivity to gaseous hydrocarbons (C 1–C 4) and olefins decreases with the increase of SiO 2 content. The spray-dried catalysts incorporated with either precipitated SiO 2 or binder SiO 2 produce more gaseous hydrocarbons and fewer olefins, while the normal-dried process and the addition of binder SiO 2 cause a great increase in selectivity to light hydrocarbons. The selectivity to oxygenates in product decreases with the increase of SiO 2 content in the catalyst. For the catalysts incorporated with binder SiO 2, the spray-dried catalyst (SPUW) produces more oxygenates than the normal dried catalyst (FMSC), whereas the spray-dried catalyst incorporated with precipitated SiO 2 (FSCP) produces the least oxygenates among all catalysts.

Effect of potassium promoter on precipitated iron-manganese catalyst for Fischer?Tropsch synthesis

A systematic study has been carried out to investigate the impact of potassium promoter on the performance of a precipitated iron-manganese catalyst for Fischer–Tropsch synthesis (FTS). Characterization technologies of N2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES) and H2 thermal gravimetric analysis (H2-TGA) were used to study the effect of potassium on the textural properties, bulk phase composition and reduction behavior. FTS reaction test was performed in a fixed bed reactor. The results of characterization showed that the addition of potassium leads to the relatively large crystallite size of α-Fe2O3 and inhibits the reduction of catalyst. The carbonization of the catalyst is enhanced with the increase in both the potassium content and the reaction temperature. A maximum in FTS and water-gas shift (WGS) activity is noted upon increasing K content (0.7 wt.% K), followed by a sharp decline in activity at the potassium level in excess of the maximum. It is found that potassium is an effective promoter to suppress the hydrogenation function of the catalyst. The selectivity to olefins is promoted and the formation of methane and light hydrocarbons is restrained with the increasing potassium level. The selectivity to oxygenates shows a rapid and monotonic decrease with the increase of potassium loading and passes through a minimum at potassium loading of 0.7 wt.%. After the point, it increases slowly with further increasing in potassium content. At the same time, increasing reaction temperature results in a monotonic decrease in the weight percent of oxygenates over the un-promoted and potassium-promoted catalysts.

Development of sulfur tolerant catalysts for the synthesis of high quality transportation fuels

In this paper, results concerning the development of sulfur tolerant catalysts for Fischer–Tropsch synthesis (FTS), C 2+ alcohol synthesis, methanol and/or DME synthesis are presented. In the FTS reaction on Fe using H 2-rich syngas such as the biomass-derived syngas, the composition of catalyst pretreatment gas and the addition of MnO on Fe had strong impacts on its sulfur resistance as well as activity. Especially the Fe/MnO catalyst pretreated with CO showed a much lower deactivation rate and a higher FTS activity than an Fe/Cu/K catalyst in the presence of H 2S. For C 2+ alcohol synthesis a novel preparation method was developed for a highly active MoS 2-based catalyst that is well known as the sulfur tolerant catalyst. Besides some metal sulfides were found to show higher CO hydrogenation activities than MoS 2. In particular, both Rh and Pd sulfides were active and selective for the methanol synthesis. Modified Pd sulfide catalyst, i.e. sulfided Ca/Pd/SiO 2, showed an activity that was about 60% of that of a Cu/ZnO/Al 2O 3 catalyst in the absence of H 2S. This catalyst preserved 35% of the initial activity even in the presence of H 2S. The sulfided Ca/Pd/SiO 2 mixed with γ-Al 2O 3 was also available for in situ DME synthesis in the presence of H 2S.

Effect of potassium promoter on precipitated iron-manganese catalyst for Fischer–Tropsch synthesis

A systematic study has been carried out to investigate the impact of potassium promoter on the performance of a precipitated iron-manganese catalyst for Fischer–Tropsch synthesis (FTS). Characterization technologies of N 2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES) and H 2 thermal gravimetric analysis (H 2-TGA) were used to study the effect of potassium on the textural properties, bulk phase composition and reduction behavior. FTS reaction test was performed in a fixed bed reactor. The results of characterization showed that the addition of potassium leads to the relatively large crystallite size of α-Fe 2O 3 and inhibits the reduction of catalyst. The carbonization of the catalyst is enhanced with the increase in both the potassium content and the reaction temperature. A maximum in FTS and water-gas shift (WGS) activity is noted upon increasing K content (0.7 wt.% K), followed by a sharp decline in activity at the potassium level in excess of the maximum. It is found that potassium is an effective promoter to suppress the hydrogenation function of the catalyst. The selectivity to olefins is promoted and the formation of methane and light hydrocarbons is restrained with the increasing potassium level. The selectivity to oxygenates shows a rapid and monotonic decrease with the increase of potassium loading and passes through a minimum at potassium loading of 0.7 wt.%. After the point, it increases slowly with further increasing in potassium content. At the same time, increasing reaction temperature results in a monotonic decrease in the weight percent of oxygenates over the un-promoted and potassium-promoted catalysts.