Structure-Activity Correlations and Solid-state Kinetic Investigations of Iron Oxide-based Catalysts Supported on SBA-15 PDF Download
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Author: Nina Sharmen Genz
Publisher:
ISBN: 9783832549244
Category :
Languages : en
Pages : 257
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Book Description
In this book, iron oxidic species supported on nanostructured silica (SBA-15) are introduced as model catalysts for deducing structure-activity correlations in selective oxidation of propene. Influence of iron loading, Fe(III) precursor, powder layer thickness during calcination, and molybdenum addition on structure and activity of Fe_{xO_{y/SBA-15 catalysts is investigated.Fe_{xO_{y/SBA-15 catalysts are characterized ex situ and in situ by a multitude of analyzing methods, i.e. XRD, DR-UV-Vis spectroscopy, N_{2physisorption, Raman and Mössbauer spectroscopy, GC-MS, X-ray absorption spectroscopy, and TPR. Moreover, applicability of solid-state kinetic analysis methods to supported iron oxidic species is shown. Results from solid-state kinetic analysis under non-isothermal conditions are particularly helpful in corroborating structure-activity correlations of Fe_{xO_{y/SBA-15 catalysts. Understanding the correlation of various synthesis parameters with structure and activity of Fe_{xO_{y/SBA-15 catalysts eventually permits obtaining improved green iron oxide catalysts for selective oxidation of propene.
Author: Nina Sharmen Genz
Publisher:
ISBN: 9783832549244
Category :
Languages : en
Pages : 257
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Book Description
In this book, iron oxidic species supported on nanostructured silica (SBA-15) are introduced as model catalysts for deducing structure-activity correlations in selective oxidation of propene. Influence of iron loading, Fe(III) precursor, powder layer thickness during calcination, and molybdenum addition on structure and activity of Fe_{xO_{y/SBA-15 catalysts is investigated.Fe_{xO_{y/SBA-15 catalysts are characterized ex situ and in situ by a multitude of analyzing methods, i.e. XRD, DR-UV-Vis spectroscopy, N_{2physisorption, Raman and Mössbauer spectroscopy, GC-MS, X-ray absorption spectroscopy, and TPR. Moreover, applicability of solid-state kinetic analysis methods to supported iron oxidic species is shown. Results from solid-state kinetic analysis under non-isothermal conditions are particularly helpful in corroborating structure-activity correlations of Fe_{xO_{y/SBA-15 catalysts. Understanding the correlation of various synthesis parameters with structure and activity of Fe_{xO_{y/SBA-15 catalysts eventually permits obtaining improved green iron oxide catalysts for selective oxidation of propene.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 175
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Author: Julian Schittkowski
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ISBN:
Category :
Languages : en
Pages :
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Author:
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ISBN:
Category :
Languages : en
Pages : 19
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The primary focus of this research is to address those issues which are keys to understanding the relationship between surface properties and catalytic activity/selectivity. These issues also impact the understanding of the origins of the enhanced catalytic properties of mixed-metal catalysts. The experimental approach utilizes a microcatalytic reactor contiguous to a surface analysis system, an arrangement which allows in vacuo transfer of the catalyst from one chamber to the other. Surface techniques being used include Auger (AES), ultraviolet and X-ray photoemission spectroscopy (UPS and XPS), temperature programmed desorption (TPD), low energy electron diffraction (LEED), high resolution electron energy loss spectroscopy (HREELS), infrared reflection absorption spectroscopy (IRAS), and scanning tunneling and atomic force microscopy (STM and AFM). This research program builds upon previous experience relating the results of single crystal kinetic measurements with the results obtained with supported analogs. As well, the authors are exploiting recent work on the preparation, the characterization, and the determination of the catalytic properties of ultra-thin metal and metal oxide films. Specifically, the program is proceeding toward three goals: (1) the study of the unique catalytic properties of ultrathin metal films; (2) the investigation of the critical ensemble size requirements for principal catalytic reaction types; and (3) the modelling of supported catalysts using ultra-thin planar oxide surfaces.
Author: Robert K. Grasselli
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 386
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Book Description
Good,No Highlights,No Markup,all pages are intact, Slight Shelfwear,may have the corners slightly dented, may have slight color changes/slightly damaged spine.
Author: Zhongqi Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 392
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Investigating and controlling the catalyst-support interfacial interaction/structure and their effects on catalytic performance are crucial for optimizing the activity, selectivity, and durability of catalytic materials, as the heterogeneous catalytic reactions typically take place on the catalyst surface and/or at the interface between the catalyst and support. Ceria (CeO2), due to its remarkable redox activity, has been widely adopted as an active support material or promoter in a multitude of redox catalytic reactions and is the focus of this research. With the goal of bridging the predictable catalyst design-fundamental understanding of performance-practical application, we expect to develop uniform and well-defined CeO2 nanostructures as model supports to investigate the underlying mechanism of the catalyst-support interactions, and furthermore establish the correlation between interfacial structure and catalytically active sites. In Chapter 2, reducible CeO2 nanorods and nanocubes, as well as irreducible SiO2 nanospheres supported cobalt oxides (CoOx) catalysts were synthesized and comparatively studied to understand the effects of support morphology, surface defect, support reducibility, in addition to the CoOx-support interactions on their redox and catalytic properties. Chapter 3 focuses on exploring the role of “bimetallic catalysts-support interaction” over highly active CeO2 nanorods supported pure cobalt oxides and cobalt-based bimetallic oxides nanoparticles (Fe-Co, Ni-Co and Cu-Co). The interactions between cobalt with the second transition metals (Fe, Ni and Cu) are discussed as well. Nanoparticle agglomeration issue always exists when using wet-chemical methods to synthesize CeO2 nanomaterials, which is harmful for catalytic applications due to decreased surface area. Therefore, Chapter 4 presents a scalable and facile electrospinning process for designing novel fibrous structured CeO2 and one-pot synthesis of high-surface-area, thermally stable and low-temperature active Ru-CeO2 nanofiber catalysts. Besides, attracted by the great interest of three-dimensional (3D) nanoarray structures fabrication towards novel and high-performance catalyst design, as well as nanodevice applications, electrochemical deposition technique was adopted for fabricating CeO2 nanoarrays in Chapter 5. Processing factors on growing controllable CeO2 nanoarrays, including the current density, reaction temperature, stirring rate, anode and substrate types were comprehensively investigated. A scale-up synthetic strategy for CeO2 nanoarrays fabrication is developed. Besides, possible mechanisms for morphological evolution and growth of CeO2 nanoarrays are discussed.
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Languages : en
Pages :
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Inexpensive catalysts for coal liquefaction must be developed if this process is to become economically viable. Recent emphasis has been on the use of iron-based catalysts, either in the form of nanometer-sized oxides and sulfides, or organic or water soluble compounds which have been used to impregnate the coal with dispersed iron species. In almost all cases the active form of the iron catalyst has been generated in-situ at reaction conditions in the presence of sulfur. Observation of enhanced activity with the use of sulfur and the appearance of iron-sulfides both during and after the liquefaction reactions have led to the suggestion that an iron-sulfide is the catalytically active species. In this study we investigated the effect of iron-oxyhydroxide catalyst precursor phase on the bond scission ability of the catalysts produced in-situ in the presence of sulfur with the model compounds naphthyl bibenzylmethane (NBBM), bibenzyl (BB), diphenylmethane (DPM) and dibenzothiophene (DBT). The catalyst precursors investigated were ferric oxyhydroxysulfate (OHS), goethite ([alpha]-FeOOH), akaganeite ([beta]-FeOOH) and six-line ferrihydrite. These precursors were chosen for their enhanced activity for carbon-carbon bond scission with NBBM over other iron-oxyhydroxides and iron-oxides. The reactions of these catalyst precursors with the model compounds were investigated both with and without a hydrogen-donating solvent.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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The catalytic mechanism of highly active, nanophase, iron-based coal liquefaction catalysts was investigated using a series of model compounds. The iron-oxide phases ferric oxyhydroxysulfate (OHS), 6-line ferrihydrite, hematite, and goethite, were evaluated as catalyst precursors with systematically substituted diphenylmethanes in the presence of a hydrogen donating solvent. The activity of the catalysts was observed to be dependent upon the functionality on the model compounds. The results of these model compound studies and their relationship to possible reaction mechanisms are presented.
Author: Griffin John Kennedy
Publisher:
ISBN:
Category :
Languages : en
Pages : 100
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Kinetic measurements are paired with in-situ spectroscopic characterization tools to investigate colloidally based, supported Pt catalytic model systems in order to elucidate the mechanisms by which metal and support work in tandem to dictate activity and selectivity. The results demonstrate oxide support materials, while inactive in absence of Pt nanoparticles, possess unique active sites for the selective conversion of gas phase molecules when paired with an active metal catalyst. In order to establish a paradigm for metal-support interactions using colloidally synthesized Pt nanoparticles the ability of the organic capping agent to inhibit reactivity and interaction with the support must first be assessed. Pt nanoparticles capped by poly(vinylpyrrolidone) (PVP), and those from which the PVP is removed by UV light exposure, are investigated for two reactions, the hydrogenation of ethylene and the oxidation of methanol. It is shown that prior to PVP removal the particles are moderately active for both reactions. Following removal, the activity for the two reactions diverges, the ethylene hydrogenation rate increases 10-fold, while the methanol oxidation rate decreases 3-fold. To better understand this effect the capping agent prior to, and the residual carbon remaining after UV treatment are probed by sum frequency generation vibrational spectroscopy. Prior to removal no major differences are observed when the particles are exposed to alternating H2 and O2 environments. When the PVP is removed, carbonaceous fragments remain on the surface that dynamically restructure in H2 and O2. These fragments create a tightly bound shell in an oxygen environment and a porous coating of hydrogenated carbon in the hydrogen environment. This observation explains the divergent catalytic results. Reaction rate measurements of thermally cleaned PVP and oleic acid capped particles show this effect to be independent of cleaning method or capping agent. In all this demonstrates the ability of the capping agent to mediate nanoparticle catalysis. With this established the hydrogenation of furfural by Pt supported on SiO2 and TiO2 was investigated by an approach combining reaction studies with SFG in order to gain molecular level insight into the nature of the metal-support interaction. This is the first instance of SFG being used to probe the factors governing selectivity in a supported catalyst system. This work revealed that TiO2 possessed sites that, while inactive without Pt, became highly active for the selective conversion of furfural to furfuryl alcohol. By SFG a TiO2 bound intermediate species was identified that could explain the highly selective nature of the reaction by Pt/TiO2. In combination with density functional theory calculations it was determined that furfural bound favorably to oxygen vacancy sites on the TiO2 surface through the aldehyde oxygen, which in turn activated the aldehyde group for hydrogenation by a charge transfer mechanism. This intermediate could then react with spillover hydrogen from the Pt surface to form furfuryl alcohol. In an effort to generalize this mechanism to additional molecules and reducible oxides the work was expanded to the hydrogenation of crotonaldehyde with cobalt oxide as an additional support. Reaction studies and SFG study of the Pt/TiO2, Pt/Co3O4, and Pt/SiO2 catalysts, revealed a reaction pathway for Pt/TiO2 and Pt/Co3O4 which selectively produced alcohol products, crotyl alcohol and butanol, while no alcohol production was observed for the Pt/SiO2 catalyst. A thorough study of the possible secondary reaction pathways revealed that butanol was formed in a concerted manner, rather than through sequential hydrogenation of the C=C and C=O groups. Sum frequency generation studies revealed that Pt supported on SiO2 yielded identical reaction intermediates as Pt single crystals, further cementing the passive role of SiO2. Spectra obtained from the cobalt and titanium oxide supported catalysts revealed adsorption sites exist on the oxide surfaces through which the molecule binds via the aldehyde group. These sites are believed to be the active sites for alcohol production. In the case of Co3O4 ambient pressure x-ray photoelectron spectroscopy and x-ray absorption spectroscopy reveal a reduction of the oxide surface under reaction conditions indicating the adsorption sites on the oxide exist on a reduced surface, additional evidence for the site being an O-vacancy. To better understand the interplay between the formation of the two alcohols a Pt nanoparticle density dependence study was undertaken for the Co3O4 case. It was observed that increasing the Pt density, thus increasing the ratio of interface to oxide surface sites, led to an increase in butanol and decrease in crotyl alcohol production. From this it is proposed that butanol forms at the Pt-oxide interface while the crotyl alcohol forms via the spillover mechanism at an oxide site. Lastly a before undiscovered example of encapsulation of a metal particle by an oxide support is observed for the Pt/Co3O4 system by ambient pressure x-ray photoelectron spectroscopy. Under mild conditions an encapsulated state is reached in which the oxide covers the Pt surface, yet does not inhibit reactivity. In fact the total activity of the catalyst increases dramatically and a change in product selectivity was observed. By SFG it is seen that the features of a Pt bound butyraldehyde intermediate increase in intensity, which is directly correlated to a 3-fold increase in butyraldehyde activity. This work builds on a vast knowledge of catalyst-support interactions in heterogeneous catalysis by applying in-situ techniques to yield a molecular level understanding of the surface processes.
Author: Alyssa Marie Love
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The structure of metal oxide sites on supported metal oxide catalysts has a significant impact on the performance of the catalyst. For example, silica-supported vanadium oxide-a catalyst widely studied for the oxidative dehydrogenation of propane (ODHP) to propene-has a higher selectivity towards propene when the catalyst surface is comprised of primarily dispersed VOx surface species. Conversely, as the loading of vanadium oxide is increased beyond the monolayer coverage threshold, three-dimensional V2O5 particles begin to form which lower the catalyst selectivity towards propene (at higher propane conversions) in favor of COx combustion products. For this catalytic application and for other supported metal oxides, understanding the variables that maximize the dispersion of two-dimensional metal oxide species on a support surface is invaluable information to improve the preparation of these catalysts. This thesis describes the synthesis and detailed characterization of supported oxide catalysts for the oxidative dehydrogenation of catalysts. In this work, vapor-phase grafting techniques were used to investigate the chemical reactions that occur during the synthesis of silica-supported vanadium oxide ODH catalysts. By depositing the neat vanadium precursor, VO(OiPr)3, onto silica dehydrated at 700 degrees C (called V/SiO2(700)), the complexity of variables in the synthesis was significantly decreased (compared to incipient wetness). Key anchoring and restructuring reactions during the formation of vanadium oxide sites on silica were characterized with a combination of infrared (IR), Raman, solid-state nuclear magnetic resonance (NMR), and X-Ray absorption spectroscopic studies, in addition to thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS), inductively coupled plasma (ICP) elemental analysis, etc. Afterwards, key synthesis variables (i.e., isopropanol solvent, H-bonded silanols and Na+ ions on the support surface) were incorporated into this grafting system to develop a more comprehensive model for the dispersion of vanadium oxide under wet impregnation conditions. Efforts to improve Raman sensitivity towards metal oxide surface sites with shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) are also addressed in this work. The methodology and characterization approach presented for the study of supported vanadium oxide catalysts was also applied to the study of promising new ODHP catalysts, including hexagonal boron nitride and silica-supported boron oxide catalysts.
