Investigation of Intrinsic Activity of Cobalt and Iron Based Fischer-Tropsch Catalysts Using Transient Kinetic Methods PDF Download
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Author: Alexandre Antônio Bento Carvalho Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The work exposed in this manuscript concerns the study of the intrinsic activity and localization of active sites in cobalt and iron based catalysts using a combination of transient kinetic methods such as SSITKA, extended physicochemical characterization and catalytic tests under quasi steady state conditions. Promotion of iron catalysts with metals used for soldering (Bi and Pb) results a remarkable increase in the light olefin production rate with the possibility to conduct Fischer-Tropsch synthesis at very mild reaction conditions (low pressure) and even at atmospheric pressure. Transient kinetic experiments showed facilitation of CO dissociation in the presence of promoters by scavenging O atoms from iron carbide. Cobalt catalyst supported by mordenite zeolite presented higher value of SSITKA rate constant. Localization of cobalt active sites in bifunctional cobalt-zeolite catalysts has a major impact on the reaction rate and in particular on the hydrocarbon selectivity. A proximity between the cobalt active site and Bronsted active sites was found to be a key parameter to obtain higher selectivity and yield of isomerized hydrocarbons. SSITKA combined with catalyst characterization revealed that carbon deposition and cobalt nanoparticle agglomeration were responsible for the deactivation of silica supported cobalt catalysts. Catalyst rejuvenation in hydrogen lessened the amounts of deposited carbon species and partially released the most active sites of carbon monoxide dissociative adsorption and stronger sites of carbon monoxide reversible adsorption.
Author: Alexandre Antônio Bento Carvalho Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The work exposed in this manuscript concerns the study of the intrinsic activity and localization of active sites in cobalt and iron based catalysts using a combination of transient kinetic methods such as SSITKA, extended physicochemical characterization and catalytic tests under quasi steady state conditions. Promotion of iron catalysts with metals used for soldering (Bi and Pb) results a remarkable increase in the light olefin production rate with the possibility to conduct Fischer-Tropsch synthesis at very mild reaction conditions (low pressure) and even at atmospheric pressure. Transient kinetic experiments showed facilitation of CO dissociation in the presence of promoters by scavenging O atoms from iron carbide. Cobalt catalyst supported by mordenite zeolite presented higher value of SSITKA rate constant. Localization of cobalt active sites in bifunctional cobalt-zeolite catalysts has a major impact on the reaction rate and in particular on the hydrocarbon selectivity. A proximity between the cobalt active site and Bronsted active sites was found to be a key parameter to obtain higher selectivity and yield of isomerized hydrocarbons. SSITKA combined with catalyst characterization revealed that carbon deposition and cobalt nanoparticle agglomeration were responsible for the deactivation of silica supported cobalt catalysts. Catalyst rejuvenation in hydrogen lessened the amounts of deposited carbon species and partially released the most active sites of carbon monoxide dissociative adsorption and stronger sites of carbon monoxide reversible adsorption.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
This work focuses on (1) searching/summarizing published Fischer-Tropsch synthesis (FTS) mechanistic and kinetic studies of FTS reactions on iron catalysts; (2) preparation and characterization of unsupported iron catalysts with/without potassium/platinum promoters; (3) measurement of H2 and CO adsorption/dissociation kinetics on iron catalysts using transient methods; (3) analysis of the transient rate data to calculate kinetic parameters of early elementary steps in FTS; (4) construction of a microkinetic model of FTS on iron, and (5) validation of the model from collection of steady-state rate data for FTS on iron catalysts. Three unsupported iron catalysts and three alumina-supported iron catalysts were prepared by non-aqueous-evaporative deposition (NED) or aqueous impregnation (AI) and characterized by chemisorption, BET, temperature-programmed reduction (TPR), extent-of-reduction, XRD, and TEM methods. These catalysts, covering a wide range of dispersions and metal loadings, are well-reduced and relatively thermally stable up to 500-600 C in H2 and thus ideal for kinetic and mechanistic studies. Kinetic parameters for CO adsorption, CO dissociation, and surface carbon hydrogenation on these catalysts were determined from temperature-programmed desorption (TPD) of CO and temperature programmed surface hydrogenation (TPSR), temperature-programmed hydrogenation (TPH), and isothermal, transient hydrogenation (ITH). A microkinetic model was constructed for the early steps in FTS on polycrystalline iron from the kinetic parameters of elementary steps determined experimentally in this work and from literature values. Steady-state rate data were collected in a Berty reactor and used for validation of the microkinetic model. These rate data were fitted to 'smart' Langmuir-Hinshelwood rate expressions derived from a sequence of elementary steps and using a combination of fitted steady-state parameters and parameters specified from the transient measurements. The results provide a platform for further development of microkinetic models of FTS on Fe and a basis for more precise modeling of FTS activity of Fe catalysts. Calculations using periodic, self-consistent Density Functional Theory (DFT) methods were performed on various realistic models of industrial, Fe-based FTS catalysts. Close-packed, most stable Fe(110) facet was analyzed and subsequently carbide formation was found to be facile leading to the choice of the FeC(110) model representing a Fe facet with a sub-surface C atom. The Pt adatom (Fe{sup Pt}(110)) was found to be the most stable model for our studies into Pt promotion and finally the role of steps was elucidated by recourse to the defected Fe(211) facet. Binding Energies(BEs), preferred adsorption sites and geometries for all FTS relevant stable species and intermediates were evaluated on each model catalyst facet. A mechanistic model (comprising of 32 elementary steps involving 19 species) was constructed and each elementary step therein was fully characterized with respect to its thermochemistry and kinetics. Kinetic calculations involved evaluation of the Minimum Energy Pathways (MEPs) and activation energies (barriers) for each step. Vibrational frequencies were evaluated for the preferred adsorption configuration of each species with the aim of evaluating entropy-changes, pre exponential factors and serving as a useful connection with experimental surface science techniques. Comparative analysis among these four facets revealed important trends in their relative behavior and roles in FTS catalysis. Overall the First Principles Calculations afforded us a new insight into FTS catalysis on Fe and modified-Fe catalysts.
Author: Wilson D. Shafer Publisher: MDPI ISBN: 303928388X Category : Science Languages : en Pages : 414
Book Description
Since the turn of the last century when the field of catalysis was born, iron and cobalt have been key players in numerous catalysis processes. These metals, due to their ability to activate CO and CH, haev a major economic impact worldwide. Several industrial processes and synthetic routes use these metals: biomass-to-liquids (BTL), coal-to-liquids (CTL), natural gas-to-liquids (GTL), water-gas-shift, alcohol synthesis, alcohol steam reforming, polymerization processes, cross-coupling reactions, and photocatalyst activated reactions. A vast number of materials are produced from these processes, including oil, lubricants, waxes, diesel and jet fuels, hydrogen (e.g., fuel cell applications), gasoline, rubbers, plastics, alcohols, pharmaceuticals, agrochemicals, feed-stock chemicals, and other alternative materials. However, given the true complexities of the variables involved in these processes, many key mechanistic issues are still not fully defined or understood. This Special Issue of Catalysis will be a collaborative effort to combine current catalysis research on these metals from experimental and theoretical perspectives on both heterogeneous and homogeneous catalysts. We welcome contributions from the catalysis community on catalyst characterization, kinetics, reaction mechanism, reactor development, theoretical modeling, and surface science.
Author: Andrey Skrypnik Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
This study was aimed to evaluate the fundamentals for the purposeful preparation of Fe-based catalysts for CO2 conversion to higher hydrocarbons (C2+-hcs) with suppressed methane production. To this end tailored catalyst preparation and sophisticated material characterization by state-of-the-art techniques were combined with spatially resolved steady-state and transient kinetic analyses. To determine factors governing catalytic performance, the evolution of the microstructure and the phase composition of as-prepared iron oxides under CO2 Fischer-Tropsch synthesis conditions were established.eng
Author: Israel E. Wachs Publisher: Springer Nature ISBN: 3031071255 Category : Technology & Engineering Languages : en Pages : 1109
Book Description
Co-edited by world-renowned scientists in the field of catalysis, this book contains the cutting-edge in situ and operando spectroscopy characterization techniques operating under reaction conditions to determine a materials’ bulk, surface, and solution complex and their applications in the field of catalysis with emphasis on solid catalysts in powder form since such catalyst are relevant for industrial applications. The handbook covers from widely-used to cutting-edge techniques. The handbook is written for a broad audience of students and professionals who want to pursue the full capabilities available by the current state-of-the-art in characterization to fully understand how their catalysts really operate and guide the rational design of advanced catalysts. Individuals involved in catalysis research will be interested in this handbook because it contains a catalogue of cutting-edge methods employed in characterization of catalysts. These techniques find wide use in applications such as petroleum refining, chemical manufacture, natural gas conversion, pollution control, transportation, power generation, pharmaceuticals and food processing. fdsfds
Author: Publisher: ISBN: Category : Languages : en Pages : 83
Book Description
The impact of deuterium on the Fischer-Tropsch (FT) synthesis was studied with a precipitated iron catalyst in the slurry phase. Deuterium has been used by several research groups to better understand the mechanism of CO hydrogenation. Inverse (k{sub H}/k{sub D} 1), normal (k{sub H}/k{sub D} 1) and no isotope effect (k{sub H}/k{sub D} = 1) have been reported. The conflicting results are thought to arise because rate of reaction is a combination of kinetic and equilibrium factors. In summary, the presence of boron produced only minor changes on the properties of the cobalt catalyst. In earlier studies, it was shown that the presence of boron made the catalyst less susceptible to poisoning by sulfur. Steady-state supercritical Fischer-Tropsch synthesis was studied in the work using a fixed-bed reactor and an unpromoted Co/SiO2 catalyst. This serves as the baseline for promoted catalyst studies. A pentane-hexane mixture was used as the supercritical solvent. Overall reactor pressure, syngas partial pressure and contact time were kept constant to obtain a valid comparison of the impact of solvent density in the catalytic activity and selectivity. Three different partial pressures of the mixture were chosen based on the density-pressure curve in order to investigate the pressure tuning effect to Fischer-Tropsch synthesis near critical region.
Author: Andrew Ronald Raub Publisher: ISBN: Category : Catalyst supports Languages : en Pages : 0
Book Description
This dissertation presents research done to investigate the promoter effects of small amounts of titanium oxides (TiOx) on unsupported cobalt metal catalysts for the atmospheric pressure Fischer-Tropsch (CO+H2) reaction. It is known that cobalt catalysts with TiO2 supports can have their performance for the Fischer-Tropsch reaction enhanced due to interactions between cobalt metal and the support. Small TiOx species can migrate onto the surface of metal particles during reductive treatment, termed the "strong metal-support interaction" (SMSI). Interactions between TiOx species and the cobalt metal are expected to influence its catalytic behavior. Techniques were developed to create unsupported cobalt metal catalysts dosed with controlled amounts of TiOx via oxalate precursors. By eliminating the presence of a supporting material, interactions between cobalt metal and TiOx could be focused on. This is the first time that TiOx alone has been studied as a promoter species in controlled amounts over an unsupported cobalt catalyst for the atmospheric pressure CO+H2 reaction.Steady state and chemical transient kinetic (CTK) reaction studies revealed that very small amounts of Ti (~1-2 atom%, relative to cobalt) induce changes in the catalyst structure and product selectivity. The addition of TiOx to the cobalt resulted in increased selectivity toward alkenes and suppression of CH4 and C2H6 that persisted over long reaction times. When TiOx is present, CTK measurements revealed the presence of surface intermediates that are absent over pure cobalt and react with different kinetics to form chain lengthened hydrocarbons. Estimated carbon amounts on the catalyst surfaces showed ~3 carbon atoms/cobalt metal site for pure cobalt catalysts, and ~5-6 carbon atoms/cobalt metal site for Ti-modified cobalt catalysts. General observations made about formation and decay behavior for hydrocarbon products during CTK studies were in good agreement with those obtained for similar work done on CoMgO and CoMnOx catalysts. Suggestions for the direction of future work on Ti-modified cobalt catalysts are made at the end of this dissertation.Some effort has also been spent on using methyl formate, which can be considered a liquid form of syngas, to produce chain lengthened hydrocarbons using CoMnTi catalysts. This ternary catalyst composition was selected due to its industrial relevance. Some transient kinetic studies were performed but turned out challenging to interpret due to the complexity of parallel decomposition pathways for methyl formate. In view of the complexity of the CoMnTi catalyst composition, it was deemed important to first focus on the CoTi case as a prerequisite for studying more complicated catalyst formulations.
Author: Alexandre Antônio Bento Carvalho
Author: Alexandre Antônio Bento Carvalho
Author: 
Author: Wilson D. Shafer
Author: Shiro Watanabe
Author: Andrey Skrypnik
Author: Israel E. Wachs
Author: 
Author: H. A. J. Van Dijk
Author: Ronald Alan Dictor
Author: Andrew Ronald Raub