Fischer-Tropsch synthesis using carbon dioxide, water and electricity

The Fischer-Tropsch (FT) synthesis of fuels from CO and H2 lies at the heart of the successful and mature Gas-to-Liquid technology; however its reliance on fossil resources comes with the burden of an undesirable carbon footprint. In contrast, the electroreduction of CO2 (CO2RR) powered by renewable electricity has the potential to produce the same type of fuels, but in a carbon-neutral fashion. To date, only ethylene and ethanol are attainable at reasonable efficiencies and exclusively on copper. Herein, we report that the oxygenated compounds of nickel can selectively electroreduce CO2 to C1 – C6 hydrocarbons with significant yields (Faradaic efficiencies of C3+ up to 6.5%). While metallic Ni only produces hydrogen and methane under CO2RR and FT conditions respectively, we show that polarized nickel (Niδ+) sites facilitate ambient CO2RR via the FT mechanism. The catalysts yield multi-carbon molecules with an unprecedented chain growth probability values (α) up to 0.44, which matches many technical FT synthesis systems. We anticipate that the integration of the herein proposed electrochemical-FT scheme with fuel cells may provide at this seminal stage up to 7% energy efficiency for C3+ hydrocarbons, inaugurating a new era towards the defossilization of the chemical industry.

Accumulation of liquid hydrocarbons during cobalt-catalyzed Fischer–Tropsch synthesis - influence of activity and chain growth probability

It may take over one year in order to fill FT catalyst pores, depending on activity and chain growth probability.

Kinetic aspects of chain growth in Fischer–Tropsch synthesis

Microkinetics simulations are used to investigate the elementary reaction steps that control chain growth in the Fischer–Tropsch reaction. Chain growth in the FT reaction on stepped Ru surfaces proceeds via coupling of CH and CR surface intermediates. Essential to the growth mechanism are C–H dehydrogenation and C hydrogenation steps, whose kinetic consequences have been examined by formulating two novel kinetic concepts, the degree of chain-growth probability control and the thermodynamic degree of chain-growth probability control. For Ru the CO conversion rate is controlled by the removal of O atoms from the catalytic surface. The temperature of maximum CO conversion rate is higher than the temperature to obtain maximum chain-growth probability. Both maxima are determined by Sabatier behavior, but the steps that control chain-growth probability are different from those that control the overall rate. Below the optimum for obtaining long hydrocarbon chains, the reaction is limited by the high total surface coverage: in the absence of sufficient vacancies the CHCHR → CCHR + H reaction is slowed down. Beyond the optimum in chain-growth probability, CHCR + H → CHCHR and OH + H → H2O limit the chain-growth process. The thermodynamic degree of chain-growth probability control emphasizes the critical role of the H and free-site coverage and shows that at high temperature, chain depolymerization contributes to the decreased chain-growth probability. That is to say, during the FT reaction chain growth is much faster than chain depolymerization, which ensures high chain-growth probability. The chain-growth rate is also fast compared to chain-growth termination and the steps that control the overall CO conversion rate, which are O removal steps for Ru.

Development of kinetic model for CO hydrogenation reaction over supported Fe–Co–Mn catalyst

After determining CO consumption rate, the production rate of methane, paraffin, olefin and chain growth probability factor (α) was derived and described.

Study of Syngas Conversion to Light Olefins by Response Surface Methodology

The effect of adding MgO to a precipitated iron-cobalt-manganese based Fischer-Tropsch synthesis (FTS) catalyst was investigated via response surface methodology. The catalytic performance of the catalysts was examined in a fixed bed microreactor at a total pressure of 1–7 bar, temperature of 280–380°C, MgO content of 5–25% and using a syngas having a H2to CO ratio equal to 2.The dependence of the activity and product distribution on MgO content, temperature, and pressure was successfully correlated via full quadratic second-order polynomial equations. The statistical analysis and response surface demonstrations indicated that MgO significantly influences the CO conversion and chain growth probability as well as ethane, propane, propylene, butylene selectivity, and alkene/alkane ratio. A strong interaction between variables was also evidenced in some cases. The decreasing effect of pressure on alkene to alkane ratio is investigated through olefin readsorption effects and CO hydrogenation kinetics. Finally, a multiobjective optimization procedure was employed to calculate the best amount of MgO content in different reactor conditions.

Size Control of Iron Oxide Nanoparticles Using Reverse Microemulsion Method: Morphology, Reduction, and Catalytic Activity in CO Hydrogenation

Iron oxide nanoparticles were prepared by microemulsion method and evaluated in Fischer-Tropsch synthesis. The precipitation process was performed in a single-phase microemulsion operating region. Different HLB values of surfactant were prepared by mixing of sodium dodecyl sulfate (SDS) and Triton X-100. Transmission electron microscopy (TEM), surface area, pore volume, average pore diameter, pore size distribution, and XRD patterns were used to analyze size distribution, shape, and structure of precipitated hematite nanoparticles. Furthermore, temperature programmed reduction (TPR) and catalytic activity in CO hydrogenation were implemented to assess the performance of the samples. It was found that methane and CO2selectivity and also the syngas conversion increased as the HLB value of surfactant decreased. In addition, the selectivity to heavy hydrocarbons and chain growth probability (α) decreased by decreasing the catalyst crystal size.

Studies on Cobalt-Based Catalyst to Synthesize Heavy Hydrocarbons

With incipient impregnation method, cobalt-based catalysts were prepared. The effects of the ZrO2 modification of support and the addition of the second metal Ru on heavy hydrocarbon synthesis were investigated in a fixed-bed reactor. The results revealed that, in cobalt-based catalysts modified with ZrO2, cobalt species were presented in the form of Co3O4, Zr species were highly dispersed or amorphous on the surface of the catalysts. ZrO2 addition also increased the desorption amount of CO, which was correlative with the degree of reduction of cobalt species. When the catalysts modified with ZrO2, the strong interaction between Co species and γ-Al2O3 support was replaced by a weak interaction between Co species and ZrO2. The ZrO2 modification increased the amount of easily reducible Co species. It is noteworthy that addition of a small quantity of Ru promoted the reduction of cobalt species, which led to the reduction temperature decreasing. For the 15w%Co0.4w%Ru4.3w%ZrO2/γ-Al2O3, at a reaction condition as feed gas ratio n(H2):n(CO)=2.0, 483K, 1.5MPa and 800h-1, the conversion of CO was 76.98 %, the selectivity of C5+ 88.36 %, the chain growth probability 0.86, and as to 15.0%Co0.4%Ru/γ-Al2O3, the conversion of CO was 67.15%, the selectivity of C5+ 84.41% and the chain growth probability 0.84.