Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst. / text

This thesis investigates the synthesis and activation of highly monodisperse Au25(SR)18 - clusters and bimetallic clusters (AuAg and AuPd) protected with various stabilizers for reduction and hydrogenation catalytic reactions. The first chapter is the introduction chapter, which summarizes the literature involving monolayer protected Au clusters, atomically precise Au clusters, bimetallic clusters, X-ray absorption spectroscopy, research objectives, and organization and scope. The second chapter describes the synthesis of Au25(SR)18 - clusters protected with various thiolate stabilizers for nitrophenol reduction catalysis using NaBH4 as a reducing agent. This chapter also describes the stability of these clusters under reaction conditions using UV-Vis spectroscopy and MALDI mass spectrometry. The third chapter details the synthesis of carboxylic acid-protected Au25 clusters using a NaBH4 purification strategy. Here, the knowledge obtained in the second chapter regarding the exceptional stability of Au25(SR)18 - clusters in the presence of NaBH4 was used to isolate carboxylic acid protected Au25 clusters from a polydisperse reaction mixture. The fourth chapter describes the synthesis and activation of mesoporous carbon supported Au25(SR)18 - clusters for nitrophenol reduction catalysis. Here, thermal removal of thiolate stabilizers led to the enhancement in the catalytic activity at low calcination temperatures; however, at higher calcination temperatures activity dropped as particle sintering was observed. Activation of these clusters on mesoporous carbon support was followed by TEM and X-ray absorption spectroscopy. The fifth chapter describes the thermal and chemical removal of thiolate stabilizers from supported Au25(SC8H9)18 - clusters. Here, the removal of thiolate stabilizers and subsequent growth of Au25 clusters was followed by TEM and EXAFS spectroscopy. The sixth and seventh chapters describe the synthesis of AuPd and AuAg bimetallic clusters using Au25(SR)18 - clusters as precursors and their characterization using UV-Vis spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. Here, AuPd bimetallic clusters were thermally and chemically treated, which resulted in the formation of AuPd bimetallic nanoparticles with segregated Pd atoms on the surface. AuPd bimetallic nanoparticles were used for the selective hydrogenation catalysis of allyl alcohol. The last chapter of this thesis includes final conclusions and possible avenues for future work.

Nanosized metal particles have become an important class of materials in the field of catalysis, optical, electronic, magnetic and biological devices due to the unique physical and chemical properties. This research deals with the synthesis of structured bimetallic nanoparticles for the dechlorination of toxic organics. Nanoparticle synthesis in aqueous phase for dechlorination studies has been reported. However, in the absence of polymers or surfactants particles can easily aggregate into large particles with wide size distribution. In this study, we report a novel in-situ synthesis method of bimetallic nanoparticles embedded in polyacrylic acid (PAA) functionalized microfiltration membranes by chemical reduction of metal ions bound to the carboxylic acid groups. Membrane-based nanoparticle synthesis offers many advantages: reduction of particle loss, prevention of particle agglomeration, application of convective flow, and recapture of dissolved metal ions. The objective of this research is to synthesize and characterize nanostructured bimetallic particles in membranes, understand and quantify the catalytic hydrodechlorination mechanism, and develop a membrane reactor model to predict and simulate reactions under various conditions. In this study, the PAA functionalization was achieved by filling the porous PVDF membranes with acrylic acid and subsequent in-situ free radical polymerization. Target metal cations (iron in this case) were then introduced into the membranes by ion exchange process. Subsequent reduction resulted in the formation of metal nanoparticles (around 30 nm). Bimetallic nanoparticles can be formed by post deposition of secondary appropriate metal such as Pd or Ni. The membranes and bimetallic nanoparticles were characterized by: SEM, TEM, TGA, and FTIR. A specimen-drift-free X-ray energy dispersive spectroscopy (EDS) mapping system was used to determine the two-dimensional element distribution inside the membrane matrix at the nano scale. This high resolution mapping allows for the correlation and understanding the nanoparticle structure, second metal composition in terms of nanoparticle reactivity. Chlorinated aliphatics such as trichloroethylene and conjugated aromatics such as polychlorinated biphenyls (PCBs) were chosen as the model compounds to investigate the catalytic properties of bimetallic nanoparticles and the reaction mechanism and kinetics. Effects of second metal coating, particle size and structure and temperature were studied on the performance of bimetallic system. In order to predict reaction at different conditions, a two-dimensional steady state model was developed to correlate and simulate mass transfer and reaction in the membrane pores under convective flow mode. The 2-D equations were solved by COMSOL (Femlab). The influence of changing parameters such as reactor geometry (i.e. membrane pore size) and Pd coating composition were evaluated by the model and compared well with the experimental data.

This century has seen a phenomenal growth in energy demands and environmental pollution, which has given rise to a worldwide awareness for the need to address these issues immediately. / This thesis focuses on the fabrication of high performance electrocatalysts applied in fuel cells and developing appropriate advanced oxidation processes for environmental remediation. It has been shown that ultrasonic irradiation is a promising method of synthesizing nanometre sized metal colloids with specific properties. Sonophotocatalysis has proved to be an effective process for the degradation of organic pollutants / The synthesis of platinum monometallic and platinum-ruthenium bimetallic nanoparticles was successfully achieved by using sonochemical irradiation. A chemical method and a hybrid method were used to reveal and understand the process of Ru(III) reduction by sonochemistry. TEM images of the Pt and PtRu monometallic/bimetallic particles indicate typical diameters of less than 10 nm. An effort was made to investigate the influence of two different methods, namely simultaneous and sequential sonochemical reduction, on the structure and formation of PtRu bimetallic nanoparticles. It has been shown that the sequential reduction method produces a relatively higher yield of core-shell nanoparticles than the simultaneous reduction method. It has been concluded that Pt nanoparticles, which are formed first, play an important role in catalysing the formation of Ru nanoparticles. / A number of methods including chemical, sonochemical and radiolytic synthesis were used to fabricate platinum and platinum-ruthenium monometallic/bimetallic nanoparticles. Furthermore, the evaluation of the electrocatalytic performance of these particles was performed by using cyclic voltammetry. Simultaneous and sequential methods for the synthesis of PtRu were adopted to investigate their influence on the electrocatalytic performance of these bimetallic nanoparticles. thas been shown that simultaneous reduction is an effective means of fabricating high performance electrocatalytic PtRu catalysts. A number of experiments with different ratios of platinum to ruthenium ions in precursor solution were carried out to study the effect of the ruthenium composition in platinum-ruthenium electrodes. It has been found that the methanol oxidation ability of platinum-ruthenium bimetallic nanoparticles can change with the alternation of ratio of Pt(II) to Ru(III) in the precursor solution. Simultaneous radiolytic reduction has the potential to fabricate higher performance electrocatalytic bimetallic nanoparticles. / Although both photo-oxidation and sono-oxidation techniques are fascinating solutions to the environmental problems at hand, the critical limit of these individual processes is their low efficiency of environmental remediation. In my project, sonolysis and photocatalysis (sonophotocatalysis) have been simultaneously employed to degrade selective organic pollutants in aqueous environments, such as methyl orange, p-chlorobenzoic acid, p-aminobenzoic acid and p-hydroxybenzoic acid. Experiments have been carried out in order to improve the efficiency of sonophotocatalytic reactions to ensure that a substantial amount of the electrical energy is utilized in degrading the organic pollutants. / Methyl orange, an azo dye, was selected as the degradation target for sonophotocatalysis. An orthogonal array analysis method was employed to clarify the correlation between the efficiencies of sonolysis, photocatalysis and sonophotocatalysis and the various operation conditions studied. Emphasis was placed on investigating the influence of pH and the ultrasound parameters on these three advanced oxidation processes. It was of interest to find that the degradation of methyl orange originates from hydroxylation and demethylation processes preceding aromatic ring-opening. / Sonophotocatalysis was also applied in the degradation of three aromatic carboxylic acids, p-chlorobenzoic acid, p-hydroxybenzoic acid and p-aminobenzoic acid. Experiments were carried out in order to get a thorough understanding of the synergy effects produced by combining the two oxidation techniques. A number of advanced analytical techniques, such as HPLC and Q-TOF MS/LC, were employed to comprehensively monitor and analyse the sonophotocatalytic degradation process. It has been found that synergistic effects of the combined system have been identified with respect to the parent organic pollutant as well as its degradation products. Additionally, products were quantitatively analysed by a kinetic simulation method in order to understand the reaction mechanism. This method also allowed us to quantify the synergy effects. It was observed that the solution pH played a key role in determining the degradation rate and controlling the direction of the degradation reaction. Based on the analytical data gathered, the sonophotocatalytic degradation pathway of the aromatic carboxylic acids was established. The experimental results suggest that the sonophotocatalytic technique is likely to lead to a complete mineralization of organic pollutants in aqueous solutions.

Philosophiae Doctor - PhD / Nowadays, the pollution of surface waters with chemical contaminants is one of the most crucial environmental problems. These chemical contaminants enter rivers and streams resulting in tremendous amount of destruction, so the detection and monitoring of these chemical contaminants results in an ever-increasing demand. This thesis describes the search for a suitable method for the determination of platinum group metals (PGMs) in environmental samples due to the toxicity of mercury films and the limitations with methods other than electroanalytical methods. This study focuses on the development of a novel bismuth-silver bimetallic nanosensor for the determination of PGMs in roadside dust and soil samples. Firstly, individual silver, bismuth and novel bismuth-silver bimetallic nanoparticles were chemically synthesised. The synthesised nanoparticles was compared and characterised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy, and transmission electron microscopy (TEM) analysis to interrogate the electrochemical, optical, structural, and morphological properties of the nanomaterials. The individual silver, bismuth, and bismuth-silver bimetallic nanoparticles in the high resolution transmission electron microscopy results exhibited an average particle size of 10-30 nm. The electrochemical results obtained have shown that the bismuth-silver bimetallic nanoparticles exhibit good electro-catalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible spectroscopy, Fourier-transformed infrared spectroscopy, and Raman spectroscopy results confirmed the structural properties of the novel bismuth-silver bimetallic nanoparticles. In addition the transmission electron microscopy and selected area electron diffraction morphological characterisation confirmed the nanoscale nature of the bismuth-silver bimetallic nanoparticles. Secondly, a sensitive adsorptive stripping voltammetric procedure for palladium, platinum and rhodium determination was developed in the presence of dimethylglyoxime (DMG) as the chelating agent at a glassy carbon electrode coated with a bismuth-silver bimetallic nanofilm. The nanosensor further allowed the adsorptive stripping voltammetric detection of PGMs without oxygen removal in solution. In this study the factors that influence the stripping performance such as composition of supporting electrolyte, DMG concentration, deposition potential and time studies, and pH have been investigated and optimised. The bismuth-silver bimetallic nanosensor was used as the working electrode with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. The differential pulse adsorptive stripping peak current signal was linear from 0.2 to 1.0 ng/L range (60 s deposition), with limit of detections for Pd (0.19 ng/L), Pt (0.20 ng/L), Rh (0.22 ng/L), respectively. Good precision for the sensor application was also obtained with a reproducibility of 4.61% for Pd(II), 5.16% for Pt(II) and 5.27% for Rh(III), for three measurements. Investigations of the possible interferences from co-existing ions with PGMs were also done in this study. The results obtained for the study of interferences have shown that Ni(II) and Co(II) interfere with Pd(II), Pt(II) and Rh(III) at high concentrations. The interference studies of Cd(II), Pb(II), Cu(II) and Fe(III) showed that these metal ions only interfere with Pd(II) and Pt(II) at high concentrations, with no interferences observed for Rh(III). Phosphate and sulphate only interfere at high concentrations with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. Based on the experimental results, this bismuth-silver bimetallic nanosensor can be considered as an alternative to common mercury electrodes, carbon paste and bismuth film electrodes for electrochemical detection of PGMs in environmental samples. Thirdly, this study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry (DPAdSV) of PGMs in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the SPCEs. Optimisation parameters such as pH, DMG concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng/L. The detection limit for Pd(II), Pt(II) and Rh(III) was found to be 0.07 ng/L, 0.06 ng/L and 0.2 ng/L, respectively. Good precision for the sensor application was also obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II) and 5.37% for Rh(III), for three measurements. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42- and PO43- does not interfere with Pd(II) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. These possible interference ions only interfere with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) as the supporting electrolyte solution.

Nanopartículas bimetálicas de AuPd têm mostrado excelente atividade catalítica em reações de oxidação. O entendimento dos efeitos da variação da composição e morfologia das nanopartículas bimetálicas em suas propriedades catalíticas é fundamental para a preparação de catalisadores cada vez mais ativos e seletivos. Neste trabalho foram estudadas nanopartículas bimetálicas de AuPd de composição variável suportadas sobre um suporte constituído por nanopartículas de magnetita revestidas por sílica. O efeito da calcinação e da redução com hidrogênio sobre a morfologia e composição das nanopartículas bimetálicas foi acompanhado pelas técnicas de TEM, XEDS, XAS, XRD e XPS. A correlação entre estrutura, composição e atividade catalítica dos catalisadores preparados foi estudada pelo acompanhamento de reações de oxidação de monóxido de carbono e de oxidação de álcool benzílico. As amostras não calcinadas apresentaram segregação metálica em todas as composições estudadas. Após a etapa de calcinação, maior segregação metálica foi encontrada, com a formação de óxido de paládio na superfície das nanopartículas, exceto na amostra mais rica em ouro. O tratamento das amostras oxidadas com hidrogênio foi capaz de reduzir os metais oxidados na superfície das nanopartículas, mas um enriquecimento em paládio na superfície e maior segregação entre ouro e paládio foram observados. Uma melhora na atividade catalítica na oxidação de monóxido de carbono foi observada juntamente com um aumento na composição de paládio, além disso, observou-se uma maior atividade catalítica em relação às nanopartículas não calcinadas para as amostras calcinadas e reduzidas. Para a oxidação de álcool benzílico um aumento na atividade catalítica de até cinco vezes foi observado após a calcinação dos catalisadores, com maior atividade para a amostra de composição Au1Pd2. A queda na atividade catalítica após a redução dos catalisadores mostrou que a presença de óxido de paládio na superfície das nanopartículas é fundamental para que seja observada uma maior atividade catalítica. / AuPd bimetallic nanoparticles have shown excellent catalytic performance in oxidation reactions. Understanding the effects of composition and morphology of the bimetallic nanoparticles in their catalytic properties is key for the preparation of more active and selective catalysts. In this work, we studied AuPd bimetallic nanoparticles supported over silica coated magnetite nanoparticles. The effects of calcination and reduction with hydrogen on the morphology and composition of the bimetallic nanoparticles was investigated by TEM, XEDS, XAS, XRD and XPS. The correlation between structure, composition and catalytic activity of the prepared catalysts was studied by the oxidation of carbon monoxide and benzyl alcohol. The non calcined samples showed metal segregation for all investigated compositions. After the calcination step, greater metal segregation occurred, and the formation of palladium oxide on the surface of the nanoparticles was observed, except for the most gold-rich sample. The treatment of the oxidized samples with hydrogen reduced the metal oxides on the surface of the nanoparticles, but a palladium surface enrichment and greater metal segregation between gold and palladium was observed. The catalytic activity observed for the oxidation of carbon monoxide increased with increasing palladium concentrations. An increase in catalytic activity was observed for the calcined and reduced samples when compared to their non-calcined counterparts. For benzyl alcohol oxidation, a five-fold increase in catalytic activity after calcination was observed, with a peak in catalytic activity for the Au1Pd2 sample. A drop in catalytic activity after the reduction of the oxidized catalysts with hydrogen showed that the presence of palladium oxide on the surface of the nanoparticles is fundamental for an increased catalytic activity.

In the process of biodiesel production, glycerol is produced as a byproduct in bulk amounts. The amount of glycerol supplied is larger than its demand thus stockpiling and acting as waste. As a solution, glycerol which is a highly functionalized molecule must be converted to value-added products. Several catalytic routes were thoroughly investigated including, hydrogenolysis, dehydration, pyrolysis, transesterification, etherification, carboxylation and electro-oxidation. All of these routes produce products of high economic interests. However, electro-oxidation seems to be the most promising as it runs under milder conditions and the selectivity may be easily tuned by varying the applied potential and the catalyst type. In addition, the electrical energy required may be provided by renewable energy sources. Some of the value-added products that may be produced by electrooxidation listed from highest economic value to lowest are glyceraldehyde, dihydroxyacetone, lactate, glycerate, tartronate (C₃ products) > mesooxalate, glycolate, oxalate (C₂ products) > and formate (C₁ products). Noble metals (Pt, Pd and Au) are considered to be the best for alcohol electrooxidation reactions as they present high electrocatalytic activity and selectivity. To date, research is focused on enhancing the activity and selectivity of noble metals by changing the nanoparticles morphology and adding adatoms/promoters/supports. On the other hand, these metals are non-abundant and expensive which limits their actual use in the industry. For this reason, non-noble metals (Ni and Co) have gained interest as potential alternatives. Particularly, nickel has proved to have significant activity, high durability and anti-poisoning capability for GEOR. A few studies presented enhancement in catalytic performance by varying the nanoparticles structure and adjusting the surface with a bimetallic promoter. However, there is still so much space for further research to enhance the catalytic performance and selectivity of Ni-based materials. In this thesis, carbon supported bimetallic NiₓBi₁₀₀₋ₓ [x= 100, 95, 90, 80, and 50 at.%] and Ni₉₅Bi₅/C mixed with small amounts of metal oxides (CeO₂, SnO₂ and Sb₂O₃:SnO₂) were studied for GEOR application. All catalysts were synthesized by facile sodium borohydride reduction method which can be easily scaled up. Transmission electron microscopy (TEM) and electron dispersive x-ray spectroscopy (EDS) techniques were implemented to gather physical characterizations of the as-synthesized bimetallic NiBi/C catalyst. Different electrochemical tests such as; cyclic voltammetry, linear sweep voltammetry and chronoamperometry were conducted using a conventional three electrode electrochemical cell and a potentiostat to get insight on the electrochemical performance of all catalysts. Finally, quantitative product analysis was generated by running continuous glycerol electrolysis experiments in a 25 cm2 cell accompanied by HPLC analysis. The nanoparticles size of Ni₉₅Bi₅/C was ≥6nm as determined by TEM images. Results indicated that tuning the nanoparticles size has an impact on both activity and selectivity of bimetallic carbon supported NiBi catalyst. For instance, the NiBi/C (≥6nm NP size) synthesized herein had 40% higher selectivity to C₃ products compared to NiBi/C (≤3nm NP size) reported in literature. Additionally, the selectivity of Ni-based catalysts to C₃ products were largely enhanced by developing bimetallic carbon supported NiBi catalysts of different Ni:Bi atomic ratios and adding metal oxides (CeO₂, SnO₂ and Sb₂O₃.SnO₂) to NiBi/C catalysts. Results indicate that addition of metal oxides greatly enhanced selectivity to C₃ products in the following order; Ni₉₅Bi₅/C-ATO (100%)> Ni/C-ATO (99.17%)> Ni₉₅Bi₅/C-ceria (98.05%)> Ni/C-ceria (78.29%)> Ni₉₅Bi₅/C (41.43%)> Ni/C (34.57%). However, the activity of Ni₉₅Bi₅/C-X [X=CeO₂, SnO₂, and Sb₂O₃:SnO₂] was lower than that of Ni₉₅Bi₅/C and Ni/C which was explained by the strong metal support interactions between metal oxides and nickel.

The development of new catalysts for organic synthesis is an important pursuit that enables the discovery of new and more efficient reactions and the identification of new reaction mechanisms. Cooperative catalytic systems and bimetallic catalysts represent unique approaches to catalyst development that achieve reactivity that cannot be obtained with a single catalyst or metal. These types of catalysts can activate substrates in unique ways, facilitate reactions under mild conditions, increase substrate scope, and provide access to completely new transformations. The first part of this work describes the development of a cooperative nickel-titanium-catalyzed amination of allylic alcohols. The cooperative effects of the two metals allow for mild reaction conditions that tolerate a larger substrate scope. A unique tandem cyclization amination is also shown that only takes place using both metals. Additionally, the benefits of using boron tethers are shown in the boron templated dimerization of allylic alcohols. This dimerization forms boron-protected 1,3-diols. Derivatization studies were performed that show the synthetic utility of this new transformation. The second portion of this work focuses on the development of a novel bimetallic rhodium complex and its use in organic synthesis. Using a 2-phosphinoimidazole ligand in the presence of carbon monoxide, a bimetallic Rh(II) complex is formed and purified in high yield. This complex shows versatile reactivity and performs reactions that are traditionally catalyzed by both Rh(I) and Rh(II) complexes. An X-ray crystal structure and DFT calculations confirm the bimetallic nature of this catalyst. Our catalyst shows a unique ability to perform reductive eliminations with weak nucleophiles where other rhodium catalysts perform -hydrogen elimination. The utility of this catalyst is shown in the intramolecular hydroamination of allenes to form small and medium sized nitrogen heterocycles. We also describe the development of a bimetallic trifluoroacetoxylation of allenes. This reaction only occurs with our bimetallic catalyst and over 30 examples are shown.

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No description available.