Identification and Characterization of Active Sites and Stable Surface Intermediates on Copper-based Methanol Synthesis Catalysts by Temperature-programmed Desorption and FTIR Spectroscopy PDF Download
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Author: David Lloyd Roberts
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ISBN:
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Languages : en
Pages : 346
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Author: David Lloyd Roberts
Publisher:
ISBN:
Category :
Languages : en
Pages : 346
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Category : Dissertations, Academic
Languages : en
Pages : 606
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Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 564
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Author: University of Minnesota
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Category : Dissertations, Academic
Languages : en
Pages : 254
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Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 984
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Author: Insoo Ro
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Category :
Languages : en
Pages : 156
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Previous studies have shown that the type of support and the addition of promoting materials can influence the catalytic activity and selectivity due to the formation of interfacial sites. However, the nature of the active sites and the reaction mechanisms governing these catalytic reactions are not known in detail. This is primarily because the synthesis of catalysts by traditional methods produces a wide distribution of metal particle sizes and compositions, impeding the accurate assessment on the nature of the surface, the active sites, and the catalytic behavior. Accordingly, this thesis presents the new synthetic route developed to prepare bimetallic nanoparticles with controlled particle size and interfacial sites to achieve an effective link between characterizations and reactivity. This thesis also focuses on elucidating catalytic active sites with well-defined catalysts by developing approaches to estimate the concentrations and intrinsic activity of monometallic and interfacial sites. In Chapter 3, we discuss the synthesis of well-defined Cu catalysts synthesized by controlled surface reactions (CSR) and atomic layer deposition (ALD) methods containing varying amounts of zirconia for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. We found that the dominant active sites for the production of acetaldehyde are monometallic Cu, while Cu-ZrO2 interfacial sites are necessary for the dehydrogenative coupling reaction between ethanol and acetaldehyde to produce ethyl acetate and the effective synthesis of methanol from CO2 and H2. In addition, we quantified the concentration of Cu and Cu-ZrO2 interfacial sites using a combination of sub-ambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. In Chapter 4, we prepared the supported Pt catalysts with different Mo contents by the CSR method for the reverse water gas shift (RWGS) reaction under dark and visible light illumination conditions. We demonstrated that Pt-MoOx interface formation and photoexcitation by visible light irradiation increase the catalytic activity for the RWGS reaction by alleviating CO poisoning on Pt surface. In Chapter 5, we showed that the deposition of Mo onto Au nanoparticles by the CSR method occurs preferentially on under-coordinated Au sites using reactivity measurements, CO FTIR studies, Raman spectroscopy, and X-ray absorption spectroscopy (XAS). Correlations of RWGS reactivity with changes in FTIR spectra for samples containing varying amounts of Mo indicate that interfacial sites are an order of magnitude more active than Au sites for RWGS under dark and visible light illumination conditions. In Chapter 6, we showed that the formation of Pt-FexOy interfaces by the CSR method increases the catalytic activity for the hydrogenation of carbonyl groups and CO oxidation. The presence of Pt-FexOy interfacial sites may enhance the catalytic activity by stabilization of the adsorbed reactive intermediates through bonding with C=O groups for carbonyl groups hydrogenation. The enhanced activity over Pt1Fex/SiO2 catalysts for CO oxidation compared to Pt/SiO2 can be associated with a lower energy barrier for O2 adsorption and activation over Pt-FexOy interfacial sites. We conclude with a discussion of future directions.
Author: Samuel M. Fehr
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Category :
Languages : en
Pages :
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Category : Coal
Languages : en
Pages : 744
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Category :
Languages : en
Pages : 12
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The adsorption and deactivation characteristics of coprecipitated Cu/ZnO-based catalysts were examined and correlated to their performance in methanol synthesis from CO2 hydrogenation. The addition of Ga2O3 and Y2O3 promoters is shown to increase the Cu surface area and CO2/H2 adsorption capacities of the catalysts and enhance methanol synthesis activity. Infrared studies showed that CO2 adsorbs spontaneously on these catalysts at room temperature as both monoand bi-dentate carbonate species. These weakly bound species desorb completely from the catalyst surface by 200 °C while other carbonate species persist up to 500 °C. Characterization using N2O decomposition, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX) analysis clearly indicated that Cu sintering is the main cause of catalyst deactivation. Ga and Y promotion improves the catalyst stability by suppressing the agglomeration of Cu and ZnO particles under pretreatment and reaction conditions.
Author: Lars C. Grabow
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ISBN:
Category :
Languages : en
Pages : 234
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