Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Rina Tannenbaum; Committee Co-Chair: Rosario A. Gerhardt; Committee Member: E. Kent Barefield; Committee Member: Karl I. Jacob; Committee Member: Preet Singh; Committee Member: R. Bruce King. Part of the SMARTech Electronic Thesis and Dissertation Collection.

In this study, the effect of Pt particle size on the reaction rate and selectivity of preferential oxidation of CO (PROX) reaction was investigated on Pt/Al2O3. 2% Pt/&amp / #947 / -Al2O3 catalysts were prepared by incipient wetness method / the particle size of the catalysts was modified by calcination temperature and duration. Therefore, the relative amounts of low and high coordination atoms on the metal particle surface can be changed. Over these catalysts, first, the CO oxidation reaction was studied in the absence of hydrogen. The catalyst having the highest dispersion, i.e., lowest metal particle sizes, had the highest activity as indicated by its lowest light-off temperature. On the other hand, the turnover frequencies (TOF) of the catalysts were increasing with decreasing dispersion. The activation energy of the catalysts were also compared and examined: as the particle size increased, the activation energy decreased. In the second part, preferential oxidation of CO reaction in the presence of hydrogen was studied. Both CO conversion and selectivity first increased with increasing reaction temperature, then exhibited a maximum, and finally decreased. Both CO conversion and selectivity did not show any trend for different dispersed catalysts for &amp / #955 / (2PO2/PCO) was 1. In order to reach a definite conclusion about the structure sensitivity of selective CO oxidation, the experiments with different &amp / #955 / &rsquo / s and space times over the same catalysts should be performed.

ABSTRACT PRECONCENTRATION OF SOME PRECIOUS METALS USING DEBT IMPREGNATED RESIN Refiker, H&uuml / rm&uuml / s M. Sc., Department of Chemistry Supervisor: Prof. Dr. R. Sezer Ayg&uuml / n Co-supervisor: Assoc. Prof. Dr. Melek Merdivan August 2005, 107 pages In this thesis, trace amounts of gold and silver have been determined by flame absorption spectrometry (FAAS) after preconcentration by N,N-diethyl-N&#039 / -benzoylthiourea (DEBT) impregnated resin (Amberlite XAD-16). In the first part of the thesis, sorption behaviours of gold and silver with DEBT impregnated resin under optimized conditions / stirring time, pH, desorption of metals and metal ion capacities of the resin have been studied in batch process. Metal ion capacity of resin is calculated as 0.17 mmol/g resin and 0.104 mmol/g resin for silver and for gold, respectively. In the second part of the thesis, preconcentration of gold and silver was tried by DEBT impregnated resin using column process under optimized conditions / pH, flow rate and volume of sample solution, nature of eluent, flow rate and volume of eluent However, due to partial leaching of DEBT by time, no satisfactory and reproducible results could be obtained. In the final part of the study, metal chelates prepared in aqueous solutions were passed through the column under optimized conditions and satisfactory sorption-desorption and selective preconcentration could be achieved. Under optimized conditions, silver and gold ions at the concentrations of 0.05 &amp / #61549 / g/mL and 0.015 &amp / #61549 / g/mL with preconcentration factors of 7.7 and 6.7, respectively could be determined by FAAS. The proposed method is highly selective without the need for any interference elimination process. Keywords: Precious metals, Solid-phase extraction, DEBT, Amberlite XAD-16

The first section of this thesis concerns the study of interactions between the intense local plasmonic field generated by nanostructure and a well known photosynthetic protein system, bacteriorhodopsin (bR). bR is a membrane protein responsible for proton transport. Among the many intermediates formed upon photoexcitations, two of the most relevant have been studied. The intermediates under studies were I460 and M412, and their decay dynamics were measured in presence of the plasmonic field generated by the excitation of their surface electrons using visible photons. Both intermediates decay lifetime were affected when the plasmonic field was turned on, and it was verify that thermal effect were not the source of the change in dynamic. The second part concerns the investigation of third-order nonlinearity of a series of extended conjugated squaraine dyes in the telecommunication spectral region. Their nonlinearity is measured via Degenerate Four Wave Mixing and Z-scan as function of the dyes increasing conjugation length and number of squarylium groups. The dyes produced large real and imaginary values for the third order nonlinearity in the 1300-1500 nm range which makes them attractive for optical limiting type of applications.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1986. / 4 cartes géographiques sur feuillets pliés, en pochette. CaQCU Bibliogr.: p. 58-61. Document électronique également accessible en format PDF. CaQCU

This diploma thesis focuses on the design of three portfolio variants for a fund of qualified investors operating in the Czech Republic, which focuses on investing in shares of Exchange Traded Funds investing in precious metals.

As our world continues to develop and contend with the impacts of climate change, the scale up renewable energy technologies has never been more urgent. Alternative fuels derived from biomass-derived oxygenates and water splitting offer promising solutions for the transition towards sustainable chemical feedstocks and integration of clean renewable energy sources. However, this technology continues to be hampered by the need for scarce and costly precious metal catalysts. The work done in this thesis explored the facet-dependence of glycerol electrooxidation and studied the application of earth-abundant transition metal carbides (TMCs) and nitrides (TMNs) for reducing precious metal catalyst loadings in water electrolysis and electrooxidation of methanol and glycerol. Glycerol valorization has drawn significant interest in recent years due to the growth in biodiesel production leading to the market saturation of glycerol. While this molecule can be converted into a variety of value-added products, the possibilities have been limited by poor selectivity for C-C bond scission. The breaking of the C-C bonds in glycerol allows for complete extraction of energy from the molecule via complete glycerol oxidation, thereby opening the door for utilizing glycerol as an electrochemical fuel. While platinum (Pt) has been among the most popular catalysts, its tendency for poisoning due to adsorbed CO has hindered its activity. Previously demonstrated to enhance the catalytic activity of platinum (Pt) by reducing CO binding energy and increasing C-C bond scission selectivity in ethanol electrooxidation, TMCs were employed as catalyst supports for the glycerol electrooxidation reaction. This work used electrochemical techniques and in-situ IRRAS to study various loadings of Pt/TaC and Pt/WC to find enhanced C-C bond scission activity at reduced Pt loading because of the synergistic effects between Pt and TMCs. While Pt has remained the benchmark catalyst for glycerol electrooxidation due to its high C-C scission activity, gold (Au) has also found popularity with its high catalytic activity attributed to greater resistance to CO poisoning, despite its favorability for partial glycerol oxidation. Previous studies have hinted at the significance of Au surface facets on glycerol oxidation activity and product selectivity, but none had used nanoparticles with controlled surface facets. This thesis sought to bridge the knowledge gap using precisely-synthesized Au nanocrystals with well-characterized {100}, {110}, and {111} surface facets to provide insight into glycerol electrooxidation on Au. Electrochemical techniques were used in parallel with in-situ IRRAS analysis to uncover the differences in product selectivity and oxidation activity between the three Au surfaces, with Au {111} exhibiting the greatest activity for C-C bond scission, while Au {110} showed the lowest onset potential due to facile AuOH- formation. Hydrogen (H₂) fulfills a critical role in modern society, not only as a renewable fuel, but also as a key chemical feedstock. Production of H₂ from water electrolysis creates opportunities for storing excess energy from renewable sources as an energy-dense fuel and reducing the environmental footprint of chemical processes requiring H₂. However, efforts have been hampered by the dependence on scarce Pt-group catalyst materials. This thesis explores the application of TMNs as an earth-abundant material for enhancing the activity of Pt in the hydrogen evolution reaction (HER). Combined with DFT calculations, the HER activity of monolayer Pt- and Au-modified TMN thin films was correlated with the ΔGH* values in a volcano-type relationship. Electrocatalytic experiments in acidic electrolyte showed that TMN-supported monolayer Pt exhibited similar HER activity to the Pt foil, correlating with intermediate hydrogen adsorption strength. TiN-supported Pt and Au powders were studied to extend the correlations from thin films. Furthermore, the electrochemical stability of TMNs was studied across a wide range of potentials and pH values to generate pseudo-Pourbaix diagrams and identify TMN candidates for HER, alcohol oxidation, ORR and OER applications. Using the pseudo-Pourbaix findings, Pt/TMN catalysts were selected for studying methanol electrooxidation activity. Methanol electrooxidation has drawn significant attention particularly due to interest in direct alcohol fuel cells. Much like the case for glycerol oxidation, while Pt has been the benchmark catalyst, it has been hindered by strong adsorption of CO. As the modification of Pt with other materials, such as ruthenium, has shown promising enhancements to methanol electrooxidation activity, the synergistic effects of Pt modification with TMNs were studied in this work. In the resulting electrochemical experiments, Pt/Mo₂N was found to exhibit negligible activity likely because of its oxidative instability. In contrast, Pt/TiN showed enhanced activity, and in-situ IRRAS experiments suggest that Pt/TiN enhanced the COads-free pathway leading to increased formic acid selectivity. This thesis demonstrated avenues for developing more optimized catalysts with reduced loadings of Pt and other precious metals for applications in alternative fuel production and utilization. The influence of Au surface facets on glycerol oxidation was examined and the synergistic effects between Pt and earth-abundant TMC and TMN materials were used to enhance the electrooxidation of biomass-derived oxygenates and H₂ production from water electrolysis. These electrochemical stability and activity trends can guide future catalyst design for other critical reactions such as oxygen evolution and challenging applications like glycerol electroreduction.

The search for mineral deposits is a time consuming, risky and very expensive process. Applying new models and methods provides a competitive advantage in the search for mineral deposits because an explorationist can quickly evaluate potential targets and eliminate areas without good potential for mineralization. This dissertation presents a practical technique for prediction to finding precious metal mineralization at Guanajauato mining district (GMD) base on theoretical and experimental studies of fluids properties, mineral phase equilibrium, physical and chemical mechanisms. Making the technique highly transportable so that it can be applied in the field during an exploration program base on petrographic characteristics of mineral textures produced during boiling events in quartz, calcite and adularia, and fluid inclusions contained in these phases. While this work was conducted in GMD, the results should be applicable in exploration for epithermal deposits worldwide. The GMD is one of the largest silver producing districts in the world. Ore shoots are localized along three major northwest trending vein systems, the La Luz, Veta Madre and Vetas de la Sierra. More than 1200 samples were collected from surface outcrops, underground mine and historical and recent drill core. Traverses perpendicular to veins in all system were also conducted. Most of the samples (approximately 90%) were also assayed for Au, Ag, Cu, Pb, Zn, As, Sb. Samples from the GMD show a wide range in silica textures are indicative of rapid precipitation, such as occurs when fluids boil. Other mineral phases, including illite, rhombic adularia and bladed calcite are also indicative of rapid growth in a hydrothermal system and are characteristic of boiling systems. Because boiling is an effective mechanism for precipitating gold and silver from hydrothermal fluids, the presence of mineral textures indicative of boiling is a desirable feature in exploration. In many samples, textural evidence for boiling is supported by coexisting liquid-rich and vapor-rich fluid inclusions, or Fluid Inclusion Assemblages consisting of only vapor-rich inclusions, suggesting "flashing" of the hydrothermal fluids. Textural and fluid inclusion evidence for boiling has been observed in the deepest levels of the GMD, suggesting that additional precious metal resources may occur beneath these levels. / Ph. D.

Adsorption mechanisms of modified thiol collectors on gold, silver, and gold-silver alloys have been studied and compared with those of ethyl xanthate (EX). The modified thiol collectors include dicresyl monothiophosphate (DCMTP), dialkyl dithiophosphinate (DTPI) and monothiophosphinate (MTPI). In general, the adsorption mechanisms on silver and gold-silver alloys can be explained by the EC-mechanism involving an electron transfer step and a chemical reaction step. Thus, the adsorption should be controlled by the Eh of the electrochemical oxidation of the electrode involved and the pK of the metal collector complex. According to this mechanism, DCMTP should adsorb on silver and gold-silver alloys at a lower potential than DTPI and MTPI since the pK of silver-DCMTP complex is larger than those of silver-DTPI and silver-MTPI. This has been verified to be the case by voltammetry, FTIR and contact angle studies. Likewise, EX adsorbs on silver at a lower potential than the modified thiol collectors because the pK of silver-EX is larger than those of the silver-modified thiol collectors. Both EX and the modified thiol collectors adsorb on silver at lower potentials than on the gold-silver alloys, which can be attributed to the lower activity of silver on the alloy surface. For the same reason, the potential for the onset of collector adsorption on alloys decreases with increasing silver content. / Ph. D.

Thesis (MBA (Business Management))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa has historically benefited from its mineral wealth, building one of the leading mining industries in the world. South Africa holds the worlds largest known PGM (or precious group metals) resource base (in a geological formation known as the Bushveld Igneous Complex), with an estimated life of 230 years (at current mining rates). This precious commodity is a precious source of both the direct as well as indirect contributions into the South African economy, as well as a leading source of employment in the South African mining industry. PGMs are predominantly used in auto catalysts, with an estimated 60% of global demand emanating from this application, where the commodity is used in breaking down noxious compounds in exhaust emissions. Given the strong correlation between automotive production and platinum sales, it seems viable to assume that platinum sales will continue to grow as more stringent legislation is introduced globally to reduce automotive emissions. This can currently only be down by increasing the platinum loads in auto catalysts, as alternative technologies are not widely accepted or developed at present. Given the influence (and positive correlation between) demand and prices, it appears that PGM prices will be driven upwards as demand continues to grow. This effect may be exacerbated by the fact that the expansion in demand is likely to outgrow the expansion in supply, given that few significant platinum operations have been started in recent years. Following the strong rally of commodity prices, specifically PGM prices in mid-2008 that saw platinum at a record high of USD2276/oz, major automotive producers have indicated that they are investigating alternatives to the application of precious metals in catalytic converters, in an attempt to curtail production costs. Although no viable substitute could be developed as yet, various alternatives (such as silver alloys) have been mentioned throughout the media. The purpose of this paper is to investigate the impact of such a substitution event on South African PGM producers and its resultant effect on the South African economy. The study will attempt to determine, at a high level, the direct impact of the event, as well as the indirect consequences of the proposed substitution event. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse ekonomie is histories op die mynbou- en landbousektore gebaseer, wat gelei het tot Suid-Afrika se wêreldklas mynbou industrie. Suid-Afrika beskik oor die wêreld se grootste PGM reserwes (in 'n geologiese formasie, ook bekend as die Bosveld Stollings Kompleks), met ‘n geskatte lewe van 230 jaar (teen huidige mynbou tempo's). Die komoditeite is verantwoordelik vir ‘n aansienlike hoeveelheid direkte en indirekte waardetoevoeging tot die Suid-Afrikaanse ekonomie. PGM’s word hoofsaaklik in katalisators in voertuie gebruik, met nagenoeg 60% van wêreldwye vraag wat uit die toepassing voortspring. PGMs word gebruik om uitlaatgasse op te breek en te verwerk in motorvoertuie. Gegewe die hoë mate van korrelasie tussen PGM en voertuigverkope, blyk dit voor die handliggend dat platinumverkope sal aanhou styg soos wat omgewingswetgeging in bepaling van toelaatbare uitlaatgasse in motorvoertuie strenger word. Die vermindering van uitlaatgasse is huidiglik slegs moontlik deur die verhoging van PGM ladings in katalisators, gegewe dat alternatiewe tegnologieë nog nie ver genoeg gevorder is om geimplementeer te word nie. Die hoë mate van korrelasie tussen PGM pryse en PGM vraag dui dat dit hoogs waarskynlik is dat die prys van edelmetaal sal aanhou styg soos wat vraag toeneem. Die verskynsel sal moontlik verder bou op die verwagting dat vraag vir die metaalaanbod oor die langtermyn sal oorskadu, siende dat geen wesenlike nuwe PGM myne onlangs oopgemaak is nie. Voertuigvervaardigers het aangedui dat hul alternatiewe tegnologieë opndersoek, nadat die platinumprys tot 'n rekord hoogtepunt van USD2276/ oz gestyg het in mid 2008. Die uitspraak is gelewer met die oog op koste kontrole in die vervaardiging van motorvoertuie. Alhoewel geen werkbare alternatief vir die edelmetale huidiglik bestaan nie, is verskeie moontlike materiale reeds in die media bespreek (byvoorbeeld verskeie silwer allooie). Die doel van die dokument is om die potensiële impak van so ‘n vervangings senario op die Suid-Afrikaanse ekonomie te ondersoek. Die studie sal poog om op ‘n hoë vlak die direkte en indirekte gevolge van die gebeurtenis te bepaal.