No description available.

No description available.

No description available.

Hydrogen is a promising renewable fuel for producing energy in transportation and domestic applications. This study investigates the production of H2 from reforming of liquefied petroleum gas (LPG). LPG is a mixture of gases, mainly propane and butane, produced from petroleum or natural gas. It is a liquid under moderate pressure and therefore a favourable feedstock for distributed hydrogen production since it is easy to store and transport with a distribution network already in place. With its wide range of propane and butane compositions world wide, in this study LPG was considered as a mixture of propane and butane. H2 production from LPG was investigated through oxidative steam reforming of propane and butane. Oxidative steam reforming (OSR) can be viewed as a combination of two reactions: partial oxidation (PO) and steam reforming (SR). By carefully controlling the steam to carbon (S/C) and oxygen to carbon (O2/C) ratios in the feed, OSR can produce higher H2 yields than PO at operational temperatures lower than SR. In the first part of this study, based on the literature and preliminarily experiments, two Ni based bimetallic catalysts, Pt-Ni/Al2O3 and Mo-Ni/Al2O3, were selected to be compared to a monometallic 15 wt% Ni/Al2O3 catalyst for OSR of a 1:1 propane to butane LPG mixture under different operational conditions. This catalysts screening study evaluated the performance of the catalysts on the basis of a statistical factorial experimental design. The factorial design was efficient in optimizing experimental runs, while testing the activity and product distribution of the catalysts at different operational limits. The importance of the factorial design was clearer when analyzing results for the Pt-Ni catalysts, as the catalyst showed different product compositions at the two selected loadings (0.2 and 1 wt%) under different conditions compared to the unpromoted catalyst. However, at both loadings, the Pt-Ni catalyst did not have a significant effect on fuel conversion or catalyst selectivity to different products. On the other had, under all stable conditions in the factorial design experiments, the Ni-Mo catalyst had higher H2 and CO yields and lower CH4 yields compared to the unpromoted catalyst. To our knowledge these product composition variations were not reported before in the literature for hydrocarbon reforming reactions over Mo promoted catalysts. The catalyst screening study also included time on stream catalysts stability tests. These experiments illustrated the high potential for solving the Ni stability problem associated with LPG reforming as the unpromoted 15Ni catalyst suffered from deactivation by coking and could not sustain its high conversion. On the other hand, promoting the Ni catalysts with 1 wt% Pt or 0.1 wt% Mo improved the catalyst resistance to coking and sustained its activity and product composition throughout the 18 hours of the stability tests. However, an increase in the Mo loading to 0.3 wt% in the Mo-Ni bimetallic catalyst, led to lower fuel conversions and loss of stability with time. Because of the interesting performance of the Mo-Ni /Al2O3 catalyst observed in the catalyst screening tests, and the lack of explanations of different aspects of this performance in the literature, especially in the presence of O2, the second part of the study was concerned with the investigation of the effect of small amounts of Mo addition on the activity, selectivity and stability of Ni catalysts when used for H2 production from LPG OSR. Individual fuels and reactions experiments showed that butane OSR gave the highest fuel conversions and H2 production rates. These experiments also revealed the importance of O2 for the catalyst activity and stability as for both hydrocarbons the catalyst suffered deactivation by coking under SR conditions. However, O2 compositions in the feed should be carefully optimized as characterization of fresh and aged catalysts showed that the loss of stability observed earlier in the catalyst screening tests for higher Mo catalysts loading, was caused by the oxidation of active Ni species to inactive Ni and Ni-Mo phases which resulted from the oxidative environment of the reaction during aging. In the last part of this study, surface and bulk properties of the monometallic Ni catalyst was compared to the Mo-Ni bimetallic catalyst using different catalyst characterization techniques ( TPR, TPO, TGA, XRD, H2 and O2 chemisorption and DRIFTS) in order to understand the structural effect of Mo addition on the catalytic properties. It was found that the improvements in the catalytic properties of the catalyst and the change in its selectivity to different products were caused by an electronic effect of Mo and its different oxide phases on Ni species. These electronic effects enhanced the O2 mobility over the catalysts surface leading to higher gasification rates of CHx species and hence, preventing coking of the catalyst. They also affected the stability of adsorbed reaction intermediates over the catalysts surface which affected the selectivity of the catalyst to different reaction products.

Hydrogen is a promising renewable fuel for producing energy in transportation and domestic applications. This study investigates the production of H2 from reforming of liquefied petroleum gas (LPG). LPG is a mixture of gases, mainly propane and butane, produced from petroleum or natural gas. It is a liquid under moderate pressure and therefore a favourable feedstock for distributed hydrogen production since it is easy to store and transport with a distribution network already in place. With its wide range of propane and butane compositions world wide, in this study LPG was considered as a mixture of propane and butane. H2 production from LPG was investigated through oxidative steam reforming of propane and butane. Oxidative steam reforming (OSR) can be viewed as a combination of two reactions: partial oxidation (PO) and steam reforming (SR). By carefully controlling the steam to carbon (S/C) and oxygen to carbon (O2/C) ratios in the feed, OSR can produce higher H2 yields than PO at operational temperatures lower than SR. In the first part of this study, based on the literature and preliminarily experiments, two Ni based bimetallic catalysts, Pt-Ni/Al2O3 and Mo-Ni/Al2O3, were selected to be compared to a monometallic 15 wt% Ni/Al2O3 catalyst for OSR of a 1:1 propane to butane LPG mixture under different operational conditions. This catalysts screening study evaluated the performance of the catalysts on the basis of a statistical factorial experimental design. The factorial design was efficient in optimizing experimental runs, while testing the activity and product distribution of the catalysts at different operational limits. The importance of the factorial design was clearer when analyzing results for the Pt-Ni catalysts, as the catalyst showed different product compositions at the two selected loadings (0.2 and 1 wt%) under different conditions compared to the unpromoted catalyst. However, at both loadings, the Pt-Ni catalyst did not have a significant effect on fuel conversion or catalyst selectivity to different products. On the other had, under all stable conditions in the factorial design experiments, the Ni-Mo catalyst had higher H2 and CO yields and lower CH4 yields compared to the unpromoted catalyst. To our knowledge these product composition variations were not reported before in the literature for hydrocarbon reforming reactions over Mo promoted catalysts. The catalyst screening study also included time on stream catalysts stability tests. These experiments illustrated the high potential for solving the Ni stability problem associated with LPG reforming as the unpromoted 15Ni catalyst suffered from deactivation by coking and could not sustain its high conversion. On the other hand, promoting the Ni catalysts with 1 wt% Pt or 0.1 wt% Mo improved the catalyst resistance to coking and sustained its activity and product composition throughout the 18 hours of the stability tests. However, an increase in the Mo loading to 0.3 wt% in the Mo-Ni bimetallic catalyst, led to lower fuel conversions and loss of stability with time. Because of the interesting performance of the Mo-Ni /Al2O3 catalyst observed in the catalyst screening tests, and the lack of explanations of different aspects of this performance in the literature, especially in the presence of O2, the second part of the study was concerned with the investigation of the effect of small amounts of Mo addition on the activity, selectivity and stability of Ni catalysts when used for H2 production from LPG OSR. Individual fuels and reactions experiments showed that butane OSR gave the highest fuel conversions and H2 production rates. These experiments also revealed the importance of O2 for the catalyst activity and stability as for both hydrocarbons the catalyst suffered deactivation by coking under SR conditions. However, O2 compositions in the feed should be carefully optimized as characterization of fresh and aged catalysts showed that the loss of stability observed earlier in the catalyst screening tests for higher Mo catalysts loading, was caused by the oxidation of active Ni species to inactive Ni and Ni-Mo phases which resulted from the oxidative environment of the reaction during aging. In the last part of this study, surface and bulk properties of the monometallic Ni catalyst was compared to the Mo-Ni bimetallic catalyst using different catalyst characterization techniques ( TPR, TPO, TGA, XRD, H2 and O2 chemisorption and DRIFTS) in order to understand the structural effect of Mo addition on the catalytic properties. It was found that the improvements in the catalytic properties of the catalyst and the change in its selectivity to different products were caused by an electronic effect of Mo and its different oxide phases on Ni species. These electronic effects enhanced the O2 mobility over the catalysts surface leading to higher gasification rates of CHx species and hence, preventing coking of the catalyst. They also affected the stability of adsorbed reaction intermediates over the catalysts surface which affected the selectivity of the catalyst to different reaction products.

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.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / The autothermal reforming and partial oxidation of hexadecane via Pt/Ni bimetallic nanoparticles on various ceria-based supports were investigated. Nanoparticles with Pt/Ni molar ratios ranging from 0/100 to 10/90 were loaded on ceria-based supports including cerium oxide, gadolinium-doped cerium oxide and cerium-doped zirconium oxide. The effect of the Pt/Ni molar ratio and the promotional effect of the support were studied by comparing the hydrogen yield. TPR and XPS analysis showed that there was a strong interaction between Ni and the CeO₂-ZrO₂ support, which led to enhancement of catalyst performance when the Pt/Ni ratio was low. The strong interaction between Ni and CeO₂-ZrO₂ support was induced by the formation of a solid solution between NiO and ZrO₂. In the case of bimetallic catalysts loaded on Gd₂O₃-CeO₂, no significant improvement in the catalytic activity of autothermal reforming was achieved until the Pt/Ni ratio reached 10/90. With C-snarf-1 as a pH-sensitive fluorescent probe, the local acidity on the surface of gradient aluminosilicate thin films and in the pore structure of mesoporous silicate films was explored. The single molecule emission ratio (I₅₈₀/I₆₄₀) of C-snarf-1 on the gradient aluminosilicate films showed similar results as previously reported for aluminosilicate mesoporous films. As the Al/Si ratio increases, the emission ratio declines, indicative of increased material acidity. In the case the mesoporous silicate films, much broader distributions of emission ratios were observed and are suggestive of significant heterogeneity in the pore structure of these films. The average emission ratio increased with a rise in pH until pH 6 or 7. A further rise in pH leads to a decline in emission ratio. Molecules with high mobility showed a narrow distribution and slightly lower average emission ratio when compared to data from all detected molecules. This observation implies a reduced heterogeneity for mesopores in which the molecules rapidly diffuse. The narrow distribution and lower average value of emission ratio at low pH, combined with the decrease in emission ratio induced by an increase in ionic strength may further indicate that the interaction between dye molecules and the pore surface impacts the emission ratio of the dye molecules.

Catalisadores de ouro tem despertado bastante interesse nos últimos anos devido à elevada seletividade apresentada na hidrogenação de moléculas multifuncionais, proporcionando assim uma síntese química mais limpa. No entanto, esses catalisadores exibem uma atividade muito menor do que os metais do grupo VIII, devido à sua capacidade limitada de dissociar H2. O paládio tem sido frequentemente combinado ao ouro para atuar em reações de hidrogenações catalíticas, devido à sua elevada capacidade de adsorver e dissociar o hidrogênio molecular, resultando em catalisadores bimetálicos AuPd que muitas vezes apresentam desempenhos catalíticos superiores aos seus homólogos monometálicos. Neste trabalho, foi estudada a ativação de nanopartículas de ouro para reações de hidrogenação pela adição de paládio, considerando a influência de ligantes estabilizantes presentes na superfície do ouro. Os catalisadores monometálicos Auw/TiO2 e Au/TiO2 foram sintetizados através da imobilização de nanopartículas pré-formadas na ausência e presença de excesso de estabilizantes (oleilamina ou hexilamina) provenientes da síntese, respectivamente. Seguindo o mesmo princípio também foram obtidos monometálicos Pd/TiO2. Catalisadores bimetálicos Auw@Pdx/TiO2 e Au@Pdx/TiO2 foram obtidos através da adição de quantidades crescentes de Pd sobre os monometálicos de ouro. Os catalisadores monometálicos apresentaram desempenhos catalíticos inferiores aos respectivos bimetálicos. Estudos iniciais na reação de hidrogenação de ciclohexeno foram fundamentais para compreender a influência da composição e do estabilizantes nas diferentes reações de hidrogenação nas quais os materiais foram aplicados. Os catalisadores livres de ligantes se mostraram ativos nesta reação, Auw@Pdx/TiO2, sendo observado um aumento da atividade à medida que a quantidade de paládio se tornava crescente, alcançando um máximo com 20% de Pd (Auw@Pd0,2/TiO2), seguida de uma diminuição da atividade com a adição de porcentagens maiores. Assim, concluiu-se que a presença de sítios de Au e Pd, além da ausência de excesso de ligantes na superfície, são significativamente importantes para tornar ativos os catalisadores Auw@Pdx/TiO2. Os catalisadores bimetálicos com ligantes na superfície, que apresentaram pior desempenho na hidrogenação de alquenos, mostraram-se promissores na semi-hidrogenação de alquinos. O catalisador contendo 1% de Pd (Au@Pd0,01/TiO2), ao ser empregado na hidrogenação de fenilacetileno, apresentou 100% de conversão e seletividades a estireno > 90%. Ao serem adicionadas porcentagens de Pd ≥ 3%, a seletividade a estireno diminui significativamente. Esta também foi alterada ao variar a quantidade de ligante (alquilamina) na superfície do catalisador bimetálico e independe do tamanho da cadeia orgânica do ligante empregado. Finalmente, podemos concluir que sistemas catalíticos altamente ativos e seletivos podem ser obtidos controlando a quantidade de paládio adicionado ao ouro, mas a presença de ligantes estabilizantes também tem influência e não pode ser negligenciada. / Over the past few years, gold catalysts have aroused great interest among researchers due to an enhanced selectivity exhibited in the hydrogenation of multifunctional molecules, enabling greener chemical synthesis. Nevertheless, since gold has a very limited ability to dissociate molecular hydrogen, these catalysts show lower activity compared to group VIII metals. Palladium has been widely used in combination with gold in catalytic hydrogenations; due to its high ability to adsorb and dissociate molecular hydrogen, the resulting bimetallic AuPd systems often show superior performance over their monometallic counterparts. The present work embodies studies on the activation of gold nanoparticles for hydrogenation reactions by adding increasing amount of palladium, considering the influence of capping ligands on the activity and selectivity exhibited by the bimetallic Au@Pd catalysts. The monometallic Auw/TiO2 and Au/TiO2 catalysts were prepared via immobilization of preformed nanoparticles in the absence and presence of excess stabilizers (oleylamine and hexylamine) used in the synthesis, respectively. Monometallic Pd/TiO2 was also synthesized following the same principle. Bimetallic catalysts Auw@Pdx/TiO2 e Au@Pdx/TiO2 were obtained by the addition of increasing amounts of Pd on the gold monometallic catalyst. The monometallic catalysts presented lower catalytic performances than the respective bimetallics. Initial studies of cyclohexene hydrogenation were instrumental to understand the influence of the composition and the presence of stabilizers in different hydrogenation reactions where the material were applied. Ligand-free catalysts were active in this reaction, Auw@Pdx/ TiO2, and an increase in activity was observed as the amount of palladium increased, reaching a maximum at 20% Pd (Auw@Pd0.2/TiO2), followed by a decrease in activity with the addition of larger percentages. Thus, it was concluded that the presence of Au and Pd sites, in addition to the absence of excess capping ligands, are significantly important in making the catalysts active. Bimetallic catalysts containing capping ligands, which presented worse performance in the hydrogenation of alkenes, showed promising results in the semi-hydrogenation of alkynes. The catalyst containing 1 wt% Pd (Au@Pd0.01/TiO2), when used in the hydrogenation of phenylacetylene, reached 100% conversion and > 90% selectivity to styrene. When percentages of Pd ≥ 3 wt% were added, the selectivity to styrene decreases significantly. Selectivity was also altered by varying the amount of ligand (alkylamine) on the surface of the bimetallic catalyst and regardless the size of the organic chain. Finally, we can conclude that highly active and selective catalytic systems can be obtained by controlling the amount of added palladium on gold, but the presence of capping ligands is also importante and can not be neglected.

The purpose of this study is to simulate Pt&ndash / IB (IB=Ag, Au, Cu) and PtPd bimetallic catalysts with Monte Carlo method for 201, 586, 1289, and 2406 atom containing clusters in the temperature range between 298&ndash / 1000K. The simulations were based on a coordination-dependent potential model in which binary interaction parameters were used. The binary interaction parameters were determined from the available thermodynamic data and classical thermodynamics mixing rules. The equilibrium structure of the clusters was dictated as a perfect cubo-octohedral shape. In the first part of this study, Pt&ndash / Ib bimetallics were modelled in order to test the Monte Carlo program against the previously published work. In the second part of the study, the surface composition of PtPd bimetallic catalysts as a function of temperature and cluster size were estimated in order to offer further insight to the catalytic activity for CO oxidation reaction. It was found that at low temperatures Pd segregation took place on the catalyst. The Monte Carlo predictions were in good agreement with the published experimental data on the surface compositions.

121 f. / Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2013-04-12T15:31:22Z No. of bitstreams: 1 Dissertação final-Francisco Xavier Julião.pdf: 1887183 bytes, checksum: 43c99b717d99959d6c766aca8a3e7001 (MD5) / Approved for entry into archive by Ana Hilda Fonseca(anahilda@ufba.br) on 2013-05-13T17:47:56Z (GMT) No. of bitstreams: 1 Dissertação final-Francisco Xavier Julião.pdf: 1887183 bytes, checksum: 43c99b717d99959d6c766aca8a3e7001 (MD5) / Made available in DSpace on 2013-05-13T17:47:56Z (GMT). No. of bitstreams: 1 Dissertação final-Francisco Xavier Julião.pdf: 1887183 bytes, checksum: 43c99b717d99959d6c766aca8a3e7001 (MD5) Previous issue date: 2011 / CAPES / O presente trabalho investigou os efeitos das propriedades eletrônicas em catalisadores a base de Pd e Pt suportados em alumina modificada com o terra rara praseodímio, avaliando sua atividade e tolerância a compostos de enxofre na reação de hidrogenação de aromáticos. Os catalisadores foram preparados pelo método de impregnação difusional, caracterizados por FRX, DRX, DRS-UV-Vis, XPS e TPD de aminas e testados na reação de hidrogenação da tetralina, na presença de tiofeno, além da realização de um estudo termodinâmico da reação. Os testes catalíticos foram realizados em um sistema micro-catalítico pulsado. Os resultados mostraram que o catalisador Pd-Pt/Al2O3-Pr apresentou uma elevada tolerância ao tiofeno, devido a combinação dos seguintes efeitos: (i) a modificação do suporte com praseodímio, que favoreceu uma interação metalsuporte capaz de diminuir a força de ligação metal-adsorvato e favorecer as interação eletrônicas intermetálicas; (ii) o efeito sinérgico a adição de um segundo metal, paládio, em conjunto com a adição do modificador promovendo transferências eletrônicas do tipo Pt→Pd, Pt→Pr e Pd→Pr; (iii) a migração do paládio para superfície catalítica, considerando que o paládio apresenta uma maior resistência ao envenenamento por compostos sulfurados. Através do estudo da seletividade também foi verificado que as propriedades do paládio foram mais efetivas para os catalisadores bimetalicos, o qual favoreceu a formação do isômero trans-decalina. Também pode-se observar, através da relação trans/cis-decalina (estável), que o sistema bimetálico Pt-Pd sofreu pouca influência nas suas propriedades eletrônicas com a adição contínua do veneno. O sistema em estudo mostrou um efeito de conjunto, pois o catalisador Pd-Pt/Al2O3- Pr apresentou pouca sensibilidade ao envenenamento por enxofre e uma atividade moderada, para concentrações do veneno até 2500 ppm de tiofeno, mostrando-se um catalisador robusto para aplicação em processos de hidrotratamento . / Salvador