No description available.

No description available.

No description available.

Thesis (Ph.D.)-- University of Wisconsin--Madison, 2007. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)-- University of Wisconsin--Madison, 2007. / Includes bibliographical references.

Promoter effects on SBA-15 supported iron Fischer-Tropsch catalysts were investigated for their potential to improve high temperature catalyst performance. FTS catalysts promoted by manganese (0.15%-1.4%), copper (0.15%-1%), and potassium (0.5%-3%), with all percentages stated on the basis of mass percentage of final catalysts, were prepared and tested at 430°C and ambient pressure in a fixed bed reactor. Manganese showed the ability to promote the FT reaction, increasing both the CO conversion and the average chain length of hydrocarbon products. Compared to the unpromoted catalyst composed only of iron supported on SBA-15, 1.4%Mn (mass) promotion of 15% (mass) iron on SBA-15 improved CO conversion from 29% to 32%, increased alpha from 0.21 to 0.34, decreased carbon dioxide selectivity from 76% to 50%, increased C2-C4 selectivity from 9.6% to 30% and increased C5+ selectivity from 0.21% to 2.2%. Copper promotion gave increased conversion, but did not significantly affect alpha or carbon dioxide selectivity. Potassium promotion in the range of 0.5% to 3% by mass, on the other hand, had a negative effect on CO conversion at all concentrations tested.

N2O chemisorption technique for copper dispersion determination was developed and optimized for accurate and reproducible results. With this technique, the bulk oxidation of pre-reduced catalyst can be prevented by N2O decomposition at low temperature (30oC). Only surface copper atoms are oxidized. The amount of freshly oxidized surface coppers is determined from H2-back-titration of fixed oxygen.The impact of temperature and time of exposure during oxidation was studied. Measurements made at higher temperature (60oC) resulted in overestimation of copper dispersion due to oxygen diffusion into the bulk and sub-layers. Much longer exposure time may also have an impact on copper dispersion estimation.For accurate results and good precision, it is recommended to work under mild conditions (isothermal oxidation at 30oC for 45 min.The developed method was successfully applied to fresh and spent catalyst. As expected, the copper dispersion for fresh catalyst was significantly higher than copper dispersion for spent catalyst.

En la presente tesis doctoral, se ha llevado a cabo un estudio mediante la teoría del funcional de la densidad (DFT) sobre los mecanismos que gobiernan cuatro importantes procesos industriales relacionados con el amoníaco: el proceso Ostwald de producción de ácido nítrico, los procesos Degussa y Andrussow de producción de ácido cianhídrico y por último, el proceso MacArthurForrest de extracción de oro de sus minerales mediante sales de cianuro.Proceso Ostwald: Se han estudiado las barreras de activación y la termodinámica de las reacciones en el proceso de formación de NO sobre Au, Cu, Ir, Pd, Pt y Rh en las superficies (111) y (211). Asímismo, se ha estudiado el proceso sobre una aleación de PtRh como la utilizada industrialmente. Finalmente, la estabilidad termodinámica de los óxidos de platino y rodio en función de la presión de oxígeno y de la temperatura ha sido analizada.Se ha encontrado una alta selectividad a producción de NO para las superficies de Pt. Aunque Rh(211) y Pd(111) muestran una gran preferencia por la recombinación N+O respecto a la N+N, la desorción de NO está fuertemente impedida. Esto provoca que pueda disociarse de nuevo. No se ha encontrado que la adición de impurezas de Rh a la superficie de Pt favorezca la selectividad del proceso, aunque si mejora la estabilidad del material, ya que el Rh forma óxidos de mayor estabilidad que el Pt y presenta menor volatilidad.Procesos Degussa y Andrussow:Se ha realizado un estudio en el que se han determinado las barreras para las reacciones más relevantes en los procesos Degussa y Andrussow sobre la superficie Pt(111). Este estudio ha sido extendido a Au, Cu, Ir, Pd y Rh en condiciones no oxidativas.En Pt, se ha observado diferente mecanismo en función de la presencia (Andrussow) o no (Degussa) de oxígeno. En condiciones no oxidativas la recombinación de especies parcialmente hidrogenadas (CHx y NHy) y su posterior deshidrogenación es el camino de reacción más importante. En condiciones oxidativas las deshidrogenaciones están asistidas por oxígeno e hidroxilos y la población de especies cambia. De este modo, la reacción entre fragmentos poco (HC+N) o nada (C+N) hidrogenadas se convierte en el mecanismo de producción del enlace CN.Au y Cu muestran en general barreras pequeñas y reacciones exotérmicas para los procesos de recombinación. Se han determinado relaciones lineales entre las barreras de reacción para las disociaciones y la energía de adsorción del N atómico. Asímismo, se han encontrado relaciones lineales entre la energía de adsorción de las diferentes especies (CN, CNH y HCN) respecto a las energía de adsorción del átomo de C.Proceso MacArthurForrest: Para estudiar la interacción del grupo cianuro con las superficies Au(111) y (211) se ha realizado una comparación con el monóxido de carbono.Electrónicamente, la adsorción de CN en las superficies de oro es cualitativamente diferente de la de CO. La covalencia del enlace AuCN está apoyada por el análisis de cargas de Bader, las distancias de enlace y el análisis ELF. La adsorción de CN se incrementa ante la presencia de carga negativa o de compuestos electropositivos. El estudio apoya los mecanismos propuestos anteriormente, en los que la adsorción del primer grupo CN provoca la donación de un electrón a la superficie. La adsorción de un segundo grupo CN es termodinámicamente favorable y forma un precursor adecuado de la molécula soluble [Au(CN)2]. / In this dissertation, the mechanisms that govern four essential industrial processes have been studied by means of Density Functional Theory (DFT). The processes are the following: Ostwald (HNO3 production), Degussa and Andrussow (HCN production) and MacArthurForrest (gold recovery). In these processes, ammonia is the main raw material or a precursor of it.The KohnSham equations that describe the model systems have been solved by means of VASP and GPAW using the RPBE functional. These packages make use of periodic boundary conditions to simulate an infinite solid as model of the real metal surface.Ostwald Process: The first step of this process, NO formation, has been studied on the (111) and (211) surfaces of Au, Cu, Ir, Pd, Pt and Rh metals. The reactions involved have been analyzed as well in the PtRh alloy (the one used in industry). The thermodynamic stability of Pt and Rh oxides as a function of the temperature and the pressure of oxygen has been described. Finally, the volatility of these oxides has been calculated to determine catalyst loses in form of PtO2 and RhO2 gases.Good selectivity towards NO formation has been found for Pt metal. The desorption of NO has been found determinant for several metals that produce NO on the surface but hardly leaves it. The addition of Rh impurities to Pt does not increase its reactivity, but Rh oxides are more stable than Pt ones and Rh is less prone to form volatile oxides.Degussa and Andrussow Processes: The formation of CN bonds from individual atoms and hydrogenated moieties on a series of transition and noble metals has been studied there.A comprehensive study on all the possible couplings between partially hydrogenated species, CHx and NHy, on Pt(111) surface is shown. The differences between the mechanism under the distinct conditions (oxygen presence or absence) have been stressed. Under nonoxidative conditions, the coupling of partially hydrogenated species is found as the most effective way to form the CN bond on Pt. Under oxygen presence conditions, dehydrogenations are eased and C, CH and N are the most stable species.Thus, C+N and HC+N appear as the favoured paths for HCN formation.For the remainder metals, the basic steps under anaerobic conditions have been analysed. Correlations between the adsorption energy of the different species with the adsorption energy of nitrogen atom has been found. The dissociation energy for the most important reactions correlates as well with the adsorption energy of carbon atom.MacArthurForrest Process: In this Chapter, the interactions of cyanides with gold (111) and (211) surfaces have been analysed. A comparison with carbon monoxide interaction has been stated. Cyanides are the responsible of the solution of gold from its minerals by the formation of the watersoluble [Au(CN)2]molecule.On the other hand, CO affinity for metallic gold is very weak.A Bader analysis on the atomic charges and Localized Density Of States (LDOS) and Electronic Localization Function (ELF) studies are shown.Almost no interaction between CO and gold have been observed. CN bonding with gold have been described as covalent according to atomic charges, bond length and electronic analysis. The mechanism proposed by experimental works: CNadsorption, etransfer, second CNadsorption and elimination of the soluble compound, is supported by our theoretical approach.

Ph.D. (Chemistry) / Please refer to full text to view abstract

The green production of formic acid and utilization of methanol over heterogeneous catalysis system were investigated in this study. The heterogeneous catalysts are widely used in the chemical industry. They offer high stability and reusability which can enhance the production ability and lower the production cost, it can be considered as the sustainable energy solution for the future. In this work, we demonstrated several different heterogeneous catalysts for sustainable formic acid production and methanol utilization, including the heteropoly acid supported mesoporous silica catalysts and multi-function mixed metal oxide catalysts. Detailed characterizations of the final products were carried out by N2 adsorption and desorption, XRD, HR-TEM, SEM, ICP-OES, XANES, NH3- TPD, Raman spectroscopy, and FTIR to identify the chemical properties and physical properties of the catalysts. We obtained 60 % glycerol conversion and 30 % formic acid selectivity with at least 3 rounds of usages in batch system over PV1Mo/SBA-15-p-DS catalyst. Moreover, the continuous methyl formate production with significantly high formation rate (16.7) has been achieved via our CuMgO-based catalysts, and the best Cu5MgO5 catalyst gives more than 80 % methanol conversion with constant selectivity to methyl formate even after 4 catalytic test (more than 200 h), revealing their potential for industrialization. For the methanol utilization reaction, the methanol homocoupling to form dimethoxymethane (DMM) has been investigated. The redox and acidic properties of catalysts both play a critical role in this reaction and the related to different product. The supported V2O5 catalyst achieves the best catalytic performance (62.1 % conversion and 85.6 % DMM selectivity) with a Ce/Al specific ratio of 1. This research not only provided the efficient catalysts for numerous application with high activity, but also discovered the relation between the catalytic performance and the nature of the materials. These findings might further help the researcher to solve the global environmental and energy issues in the near future.