The active phase in cobalt-based Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) is an industrial catalytic process that converts a mixture of CO and hydrogen into long-chain hydrocarbons. These products are used as clean transportation fuels and chemical building blocks. The solid catalysts used in the process are complex multi-component systems. Therefore, unambiguously determining the catalytically active phase under reaction conditions remains challenging and thus a topic of debate. The active phase in cobalt-based FTS, including the reaction pathways it catalyzes, has been of industrial and academic interest for many years. It provides direct ways to control the output of the process. The delineation between an active and inactive phase is often unclear, as different phases (i.e., cobalt oxide, carbide, and metal) have different catalytic behavior. This review focuses on cobalt-based FTS materials, with a special focus on the industrially applied cobalt/TiO2 system. The various cobalt phases are reviewed and discussed with respect to the most recent literature

In Situ X-ray Raman Scattering Spectroscopy of the Formation of Cobalt Carbides in a Co/TiO2 Fischer–Tropsch Synthesis Catalyst

We present in situ experiments to study the possible formation of cobalt carbides during Fischer–Tropsch synthesis (FTS) in a Co/TiO2 catalyst at relevant conditions of pressure and temperature. The experiments were performed by a combination of X-ray Raman scattering (XRS) spectroscopy and X-ray diffraction (XRD). Two different experiments were performed: (1) a Fischer–Tropsch Synthesis (FTS) reaction of an ∼14 wt % Co/TiO2 catalyst at 523 K and 5 bar under H2 lean conditions (i.e., a H2:CO ratio of 0.5) and (2) carburization of pure cobalt (as reference experiment). In both experiments, the Co L3-edge XRS spectra reveal a change in the oxidation state of the cobalt nanoparticles, which we assign to the formation of cobalt carbide (Co2C). The C K edge XRS spectra were used to quantify the formation of different carbon species in both experiments.Peer reviewe

Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts

Kinetics-based differences in the early stage fragmentation of two structurally analogous silica-supported hafnocene- and zirconocene-based catalysts were observed during gas-phase ethylene polymerization at low pressures. A combination of focused ion beam-scanning electron microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy (IR PiFM) revealed notable differences in the distribution of the support, polymer, and composite phases between the two catalyst materials. By means of time-resolved probe molecule infrared spectroscopy, correlations between this divergence in morphology and the kinetic behavior of the catalysts' active sites were established. The rate of polymer formation, a property that is inherently related to a catalyst's kinetics and the applied reaction conditions, ultimately governs mass transfer and thus the degree of homogeneity achieved during support fragmentation. In the absence of strong mass transfer limitations, a layer-by-layer mechanism dominates at the level of the individual catalyst support domains under the given experimental conditions

Surface-Sensitive Spectroscopy of the Catalytic Hydrogenation of CO and CO2

This PhD Thesis described surface-sensitive spectroscopy as a promising analytical tool for the better understanding of reaction and deactivation mechanisms in heterogeneous catalysis. Chapter 1 introduced the basic principles of spectroscopy and catalysis, as well as how fundamental insights are obtained through spectroscopic characterization under realistic reaction conditions. We set the stage for investigating the cobalt-catalyzed CO and CO2 hydrogenation reactions. A two-pronged approach was formulated: firstly, we aimed to provide new or improved insights into the catalytically active phase. Secondly, we targeted to uncover the reaction mechanisms during the formation of (un)desired reaction products. Chapter 2 introduced nanoscale spectroscopy techniques, which are promising tools to achieve the goals formulated above. Although the academic world strives to understand the fundamental phenomena that occur on the catalysts’ surfaces, the most sensitive analytical tools are often unable to operate under the harsh reaction conditions that industrial catalysis requires. This chasm was discussed and a more realistic model system consisting of cobalt nanoparticles on titania islands was introduced. In Chapter 3, infrared and Raman spectroscopy were used to decipher the reaction mechanisms involved in hydrocarbon product formation during the CO hydrogenation with cobalt-titania catalysts. By modulating the concentration of the reactant CO, infrared spectroscopy was turned into a surface-sensitive method and consequently active species were observed during the reaction. Hydrogen-containing oxygenated species responded to the CO stimulus and thus provided evidence for the hydrogen-assisted C-O bond scission. Gold nanoparticles were used to enhance the Raman spectroscopy signal and evidence was observed for the direct C-O bond scission mechanism. The reactant modulation idea recurred in Chapter 4 to investigate the catalytically active phase and reaction mechanisms during CO2 hydrogenation with cobalt-based catalysts. We also refute the general consensus that metallic cobalt is the only active phase in heterogeneous catalysis, as cobalt oxide nanoparticles on titania performed better in terms of long-chain hydrocarbon yield compared to the metallic cobalt variant. While metallic cobalt dissociated CO2 into CO directly, cobalt oxide required hydrogen atoms to split the C-O bonds. In Chapter 5, we explored potassium promoter effects in the CO and CO2 hydrogenation reactions with cobalt-titania catalysts. The addition potassium to the cobalt-titania catalyst appeared interesting for renewable energy applications that aim to convert CO2 into long-chain hydrocarbons. Potassium made the cobalt surface slightly positively charged and enabled the conversion of CO2 into the more reactive CO molecule via the reverse water-gas shift reaction. Besides, the amount of hydrogen on the catalyst surface diminished upon the addition of potassium. In Chapter 6, a solid mineral residue from industrial biomass gasification was repurposed as a solid catalyst material. The residue contained around 15 different elements, of which iron was the most important one. Iron enabled the conversion of a gas feed mixture of CO, CO2, H2, and N2 into methane and olefins. By means of operando X-ray diffraction, the transformation of metallic iron into an iron carbide phase was associated with an increase in total carbon conversion and an improved selectivity towards the desired lower olefins

Surface-Sensitive Spectroscopy of the Catalytic Hydrogenation of CO and CO2

This PhD Thesis described surface-sensitive spectroscopy as a promising analytical tool for the better understanding of reaction and deactivation mechanisms in heterogeneous catalysis. Chapter 1 introduced the basic principles of spectroscopy and catalysis, as well as how fundamental insights are obtained through spectroscopic characterization under realistic reaction conditions. We set the stage for investigating the cobalt-catalyzed CO and CO2 hydrogenation reactions. A two-pronged approach was formulated: firstly, we aimed to provide new or improved insights into the catalytically active phase. Secondly, we targeted to uncover the reaction mechanisms during the formation of (un)desired reaction products. Chapter 2 introduced nanoscale spectroscopy techniques, which are promising tools to achieve the goals formulated above. Although the academic world strives to understand the fundamental phenomena that occur on the catalysts’ surfaces, the most sensitive analytical tools are often unable to operate under the harsh reaction conditions that industrial catalysis requires. This chasm was discussed and a more realistic model system consisting of cobalt nanoparticles on titania islands was introduced. In Chapter 3, infrared and Raman spectroscopy were used to decipher the reaction mechanisms involved in hydrocarbon product formation during the CO hydrogenation with cobalt-titania catalysts. By modulating the concentration of the reactant CO, infrared spectroscopy was turned into a surface-sensitive method and consequently active species were observed during the reaction. Hydrogen-containing oxygenated species responded to the CO stimulus and thus provided evidence for the hydrogen-assisted C-O bond scission. Gold nanoparticles were used to enhance the Raman spectroscopy signal and evidence was observed for the direct C-O bond scission mechanism. The reactant modulation idea recurred in Chapter 4 to investigate the catalytically active phase and reaction mechanisms during CO2 hydrogenation with cobalt-based catalysts. We also refute the general consensus that metallic cobalt is the only active phase in heterogeneous catalysis, as cobalt oxide nanoparticles on titania performed better in terms of long-chain hydrocarbon yield compared to the metallic cobalt variant. While metallic cobalt dissociated CO2 into CO directly, cobalt oxide required hydrogen atoms to split the C-O bonds. In Chapter 5, we explored potassium promoter effects in the CO and CO2 hydrogenation reactions with cobalt-titania catalysts. The addition potassium to the cobalt-titania catalyst appeared interesting for renewable energy applications that aim to convert CO2 into long-chain hydrocarbons. Potassium made the cobalt surface slightly positively charged and enabled the conversion of CO2 into the more reactive CO molecule via the reverse water-gas shift reaction. Besides, the amount of hydrogen on the catalyst surface diminished upon the addition of potassium. In Chapter 6, a solid mineral residue from industrial biomass gasification was repurposed as a solid catalyst material. The residue contained around 15 different elements, of which iron was the most important one. Iron enabled the conversion of a gas feed mixture of CO, CO2, H2, and N2 into methane and olefins. By means of operando X-ray diffraction, the transformation of metallic iron into an iron carbide phase was associated with an increase in total carbon conversion and an improved selectivity towards the desired lower olefins

Apoio matricial em saúde mental: fortalecendo a saúde da família na clínica da crise

O objetivo consiste em abordar o apoio matricial em saúde mental às equipes de Saúde da Família (SF) e a sua relação com as situações de crise em saúde mental. Trata-se de uma pesquisa--ação realizada com equipes de SF e com um CAPS III, na Rocinha, Rio de Janeiro. Participaram profissionais de diferentes categorias em grupos operativos de reflexão e os dados foram examinados pela análise de conteúdo. É destacada a importância de envolver a SF no que se refere à clínica da crise

The active phase in cobalt-based Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) is an industrial catalytic process that converts a mixture of CO and hydrogen into long-chain hydrocarbons. These products are used as clean transportation fuels and chemical building blocks. The solid catalysts used in the process are complex multi-component systems. Therefore, unambiguously determining the catalytically active phase under reaction conditions remains challenging and thus a topic of debate. The active phase in cobalt-based FTS, including the reaction pathways it catalyzes, has been of industrial and academic interest for many years. It provides direct ways to control the output of the process. The delineation between an active and inactive phase is often unclear, as different phases (i.e., cobalt oxide, carbide, and metal) have different catalytic behavior. This review focuses on cobalt-based FTS materials, with a special focus on the industrially applied cobalt/TiO2 system. The various cobalt phases are reviewed and discussed with respect to the most recent literature