Investigation of Gallium Promoted Pd/TiO2 Catalysts for the Selective Hydrogenation of Acetylene in the Presence of Ethylene PDF Download
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Author: Luis Fabián Peña-Orduña
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 92
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Author: Luis Fabián Peña-Orduña
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 92
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Author: Wentao Xie
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 124
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Author: Madelyn Rose Baltus Ball
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Catalytic reactions play a large role in the production of energy and products used in our modern society. In order to improve the efficiency of existing processes and make the conversion of new feedstocks, such as biomass and natural gas, possible, there exists the need for improved catalytic materials. Many active catalysts have complex active sites containing multiple components; therefore, fundamental understanding of active sites and structure-performance relationships is needed to rationally design new catalysts. The work in this dissertation is focused on catalytic synthesis of well-controlled bimetallic catalysts in order to develop structure-activity and structure-selectivity relations for different chemical transformations. A controlled surface reaction synthesis approach is used to deposit Pd onto Au, Ag, or Cu parent catalysts. These Pd bimetallic catalysts are then studied for reactions where selectivity is a main challenge, and the selective Pd structure is identified. First, AuPd/TiO2 catalysts are studied for the gas phase amination of 1-hexanol using ammonia. It was determined that there are no monometallic Pd structures on the catalysts. The Pd atoms are well diluted in the Au nanoparticles at low loadings and as the Pd loading increases, more contiguous Pd sites are formed. From reactivity studies, it is determined that both the Au and Pd contribute to the overall hexanol conversion, however the activity in enhanced for the bimetallic catalysts compared to the monometallic catalysts. This rate improvement is attributed to a geometric effect where surface intermediates are not stabilized by hydrogen bonding to adsorbed ammonia in close proximity. Furthermore, the selectivity to primary amines is increased as the loading of Pd increases in the AuPd catalysts, while lower Pd loadings favor more substituted products. The selectivity trends are hypothesized to be related to both geometric and electronic effects present in the AuPd catalyst system. Next, AgPd catalysts were studied for the hydrodechlorination of 1,2-dichloroethane. The role of the support in the formation of well-controlled bimetallic nanoparticles was investigated and it was determined that well-mixed AgPd particles were formed on a TiO2 support, while some monometallic Pd particles were also formed on C and SiO2 supports. Again, using chemisorption, XAS, and CO-FTIR, it was determined that isolated Pd atoms within the Ag nanoparticles are formed on the TiO2 support at low loadings. On the SiO2 supported catalysts, contiguous Pd species are formed. The isolated Pd species are highly selective to ethylene while the contiguous Pd species are selective to the undesired ethane. Thus, the support was determined to play an important role in tuning the AgPd structure and the resulting selectivity for hydrodechlorination. The rate of 1,2-dichloroethane conversion was determined to be related to the selectivity, with the ethylene selective catalysts exhibiting the highest turnover frequencies. Finally, AgPd and CuPd catalysts were investigated for the selective hydrogenation of acetylene. Both TiO2 and SiO2 supported catalysts were studied, and it was determined by EDS analysis that the CuPd nanoparticle composition distribution was more uniform on the SiO2 support than on the TiO2 support. IR spectra of the catalyst surface after being exposed to reaction conditions indicate the presence of numerous spectator species and it is determined that there are less sites covered by spectators for the bimetallic catalysts compared to a monometallic Pd catalyst. On the TiO2 support, the bimetallic catalysts exhibit the highest rates per gram of Pd and high ethylene selectivites above 99%. The monometallic catalysts are less than 95% selective to ethane, indicating that the alloy formation improves the ethylene selectivity; the enhanced selectivity is attributed to electronic effects in the bimetallic nanoparticles. This work enabled the development of detailed active site hypotheses for different Pd based bimetallic catalysts and provided insights into the desired structures to inform rational catalyst design. The controlled surface reaction synthesis approach and general characterization methodology can be applied to a broad range of catalyst and reaction systems to improve chemical transformations for improved production of chemicals and fuels for modern society.
Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2616
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Author: Jonathan Leon Snider
Publisher:
ISBN:
Category :
Languages : en
Pages :
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As human population and industrialization grows, so too do our global demands for fuels and chemicals. Increasing consumption of fossil fuels has led to rising CO2 levels in the atmosphere, a major challenge due to the role of CO2 as a significant greenhouse gas contributing to climate change. To address anthropogenic CO2 production, new processes to capture, sequester, and utilize carbon dioxide are needed. CO2 utilization in particular is an attractive approach as it also creates a value-added product. This utilization could take the form of direct CO2 hydrogenation or a two-step process whereby the CO2 is first converted to CO via the water-gas shift reaction. To enable these processes, the discovery and development of efficient catalysts that can selectively reduce CO and CO2 to high value, oxygenated products is necessary. Towards this goal, the investigation of new catalyst formulations is crucial. Furthermore, the characterization of these materials is necessary to understand the drivers of catalyst performance and predict future targets for study. In Chapter 3, we begin with an investigation into the design of Co-Cu catalysts for CO hydrogenation to higher alcohols. To improve control over particle properties, a liquid phase nanoparticle synthesis based on the polyol method was selected to synthesize Co2.5Cu particles, which were then supported onto a variety of metal oxide supports. The results show alloyed phases were obtained using the polyol method, resulting in selectivity towards higher alcohols, as high as 11.3% when supported on alumina. However, segregation of cobalt and the formation of cobalt carbide were observed in the catalysts after catalytic testing, which limit performance compared to the desired alloy phase. In Chapter 4, our focus shifts towards understanding the surface properties of a newly discovered Ni5Ga3 catalyst for CO2 hydrogenation to methanol. Results revealed that upon air exposure Ga migrates from the subsurface region to the surface of the nanoparticles forming a Ga-oxide shell surrounding a metallic core. Reduction of this shell results in a surface enrichment of Ga. By varying reduction temperatures, it was found that partial reductions gave low CO uptakes but high methanol activity, indicating a promotional effect of the oxide phase. In Chapter 5, the investigation into the role of metal oxides in methanol synthesis continues with a study of In-Pd catalysts. We present the promotional effect of Pd on In2O3 catalysts and investigate structure-performance relationships therein. Catalysts were synthesized with varying In:Pd ratios, and it was found that In2Pd/SiO2 showed the highest activity (5.1 umol MeOH/gInPd/sec) and selectivity toward methanol (61%). Based on microkinetic modeling, operando X-ray absorption spectroscopy and ex situ characterization, the active phase is proposed to be a bimetallic In-Pd particle with a Pd-rich core and a surface In2O3 phase. A non-precious metal containing In-Ni system was also developed and displayed similar composition-activity trends to the In-Pd system. Both palladium and nickel were found to form a bimetallic catalyst with enhanced methanol activity and selectivity relative to indium oxide. Overall, this dissertation presents catalyst syntheses, advanced characterizations, and catalytic hydrogenation experiments which led to fundamental insights into the activity and selectivity of heterogeneous, bimetallic catalysts for alcohols synthesis. This work provides key understanding towards the development of catalyst theory and materials for the hydrogenation of CO and CO2.
Author: Mark E. Davis
Publisher:
ISBN:
Category : SCIENCE
Languages : en
Pages : 432
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Discusses recent research and provides tutorial chapters on enhancing selectivity in catalysis through stereoselectivity, reaction pathway control, shape selectivity, and alloys and clusters. Presents an interdisciplinary approach to increasing selectivity in homogeneous and heterogeneous catalysis research. Includes an overview chapter that discusses the current state of the field and offers a perspective on future directions.
Author: Seung A. Kim
Publisher:
ISBN:
Category : Materials science
Languages : en
Pages : 248
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Author: Piyaporn Pongbhai
Publisher:
ISBN: 9789746360555
Category :
Languages : en
Pages : 128
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Author: Tejaswi Bhavanam
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 152
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Author:
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 190
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In this study, the effects of alumina grinding and mixed oxides (ZnO-Al2O3 and NiO-Al2O3) grinding with various Zn/Al and Ni/Al molar ratios (0.1 and 0.5) prepared by an attrition ball mill on catalytic performance of alumina supported Pd catalysts for selective hydrogenation of acetylene were investigated. It was found that catalytic performances of the Pd catalyst supported on Al2O3 milled for 12 h were superior compared to those of Pd-supported on the unmilled Al2O3. However, all the catalysts prepared from milled mixed oxides presented lower acetylene conversion and ethylene selectivity than that of the catalyst prepared from alumina milled for 12 h. From X-ray diffraction, it was suggested that varying milling time directly affected the crystallite size, surface area and acidity of alumina supports. As revealed by CO chemisorption, milling of Al2O3 supports could increase metal active sites of Pd/Al2O3 catalysts without change in the interaction between Pd and the alumina support so that the catalysts exhibited higher acetylene activity and ethylene selectivity. Moreover, increasing of acidity affected coke formation on the catalysts.
