Made available in DSpace on 2016-06-02T19:55:30Z (GMT). No. of bitstreams: 1 3665.pdf: 6614955 bytes, checksum: 38fe505ba234583972871c7ff274e981 (MD5) Previous issue date: 2011-04-28 / Universidade Federal de Sao Carlos / Colloidal Pt nanoparticles were synthesized according to an adapted procedure from Song and co-workers [1], which it was based on the reduction of dihydrogen hexachloroplatinate by ethylene glycol in a basic solution, but using two PVP/Pt = 0,2 and 10 ratio. Both the ratio lead to monodisperse platinum nanoparticles with similar sizes (2.0 and 2.8 nm). Colloidal Pt nanoparticles solutions were incorporated into alumina during sol-gel synthesis and showed different stabilities when submitted to thermal treatment in synthetic air, He and H2 atmospheres. PVP/Pt ratio added to nanoparticles after synthesis was the main parameter considered to the stability of the particles on the support. Using a minor PVP/Pt ratio lead to particles agglomerates during calcinations step in synthetic air. On the other hand, when an excess of PVP was used stable and disperse particles were obtained during a severe thermal treatment. The anchoring of particles into support during incorporation stage could be the most plausible explanation for this. Platinum nanocatalysts supported on alumina and ceriaalumina showed catalytic activity for the water gas shift reaction. CO conversion data indicated that the increasing of CeO2 loading of 12 to 20% lead to an improvement in the catalytic activity. XPS measurements after pre-treatment in H2 confirmed the presence of Pt+on the catalyst surface containing ceria, suggesting some metal-support interaction. In situ characterization techniques allowed to a better understanding of species involved into water gas shift reaction mechanism. Through X-ray absorption near edge structure in the Pt edge measurements showed reduced Pt during reaction for all catalysts, suggesting that similar electronic density of sites was present. This was also observed in CO adsorbed DRIFTS measurements. Nevertheless, XANES spectra in the Ce edge showed some changes in oxidation state of Ce during the reaction, indicating the occurrence of redox mechanism, mediated by ceria. In situ DRIFTS experiments showed little concentrations of formates and carbonates species on the catalyst surface during the reaction, suggesting that more than one mechanism may occur simultaneously. / Nanopartículas de Pt foram preparadas seguindo um procedimento adaptado de Song e colaboradores [1], cuja metodologia consistiu na redução química do ácido hexacloroplatinico pelo etilenoglicol em meio básico, porém utilizando duas razões PVP/Pt = 0,2 e 10. Ambas as razões levaram a nanopartículas de Pt com tamanho similar (2,0 e 2,8 nm) e monodispersas. As soluções coloidais de nanoparticulas de Pt foram incorporada à alumina durante a síntese sol-gel e mostraram diferentes estabilidades quando submetidas a tratamentos térmicos em ar sintético, He e H2. A razão PVP/Pt utilizada na síntese das partículas foi o fator determinante na estabilidade das partículas no suporte. A adição de uma menor razão PVP/Pt levou a aglomeração das partículas durante a calcinação em ar sintético. Por outro lado, quando um excesso de PVP foi utilizado durante a síntese das partículas as mesmas se mostraram estáveis e dispersas no suporte quando submetidas ao mais severo tratamento. Isto foi relacionado ao ancoramento das partículas ao suporte durante a etapa de incorporação. Nanocatalisadores de Pt suportados em alumina e cério-alumina apresentaram atividade catalítica para a reação de deslocamento gás-água. Dados de conversão do CO indicaram que o aumento no teor de CeO2 de 12 para 20% levou a um aumento na atividade catalítica. Medidas de XPS após a etapa de pré-tratamento em H2 confirmaram a presença de Pt+na superfície dos catalisadores contendo ceria, sugerindo alguma interação metal-suporte. Técnicas de caracterização in situ possibilitaram um melhor entendimento do mecanismo das espécies envolvidas no mecanismo da reação de deslocamento gás-água. Medidas de XANES in situ na borda da Pt confirmaram a presença de Pt reduzida durante o curso da reação para todos os catalisadores, o que sugere a presença de sítios de Pt com densidade eletrônica similar. Isto também foi observado nas medidas de DRIFTS do CO adsorvido para os catalisadores estudados. No entanto, os espectros de XANES na borda do Ce confirmaram mudanças no estado de oxidação do Ce no decorrer da reação, indicando a ocorrência do mecanismo de reação redox, mediado pela ceria. Experimentos utilizando DRIFTS in situ identificaram pequenas concentrações de espécies do tipo formiatos e carbonatos na superfície dos catalisadores durante a reação, sugerindo que mais de um mecanismo pode ocorrer simultaneamente. Palavras chave: nanoparticulas, Platina, catalisador, reação de deslocamento gás-água, PVP.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / The Water Gas Shift (WGS) reaction describes the reaction between carbon monoxide and water vapour to produce carbon monoxide and hydrogen. This work describes the application of a Palladium-Silver (Pd-Ag)-based membrane film reactor, wherein the Pd-Ag film was supported by porous stainless steel (PSS), for the potential replacement of the current multi-stage WGS reaction. The objective of this work was to develop a better understanding of impediments which are relevant to the application of Pd-Ag membrane reactor for the WGSR. The long term behaviour (hydrogen permeability and selectivity) of Pd-Ag membrane under hydrogen exposure was studied, and the use of the Pd-Ag membrane reactor to produce hydrogen through the WGSR was also performed. A detailed literature review was conducted, based on the information gathered from literature. A Permeability and WGS reaction testing stations was designed and built. A thin (20μm) 77%wtPd-23%wtAg film was purchased from Takanaka Company in Japan. The membrane film was enclosed between two stainless steel plates to form a membrane reactor. The membrane reactor was fitted at the two different testing stations.

O titanato de estrôncio (SrTiO3) é um óxido de estrutura perovskita e tem sido intensamente estudado para uso em diversas aplicações, entre elas, como suporte catalítico. Entretanto, sua utilização especificamente na reação de deslocamento gás-água ainda é pouco explorada. Esta reação é de interesse para a produção de hidrogênio livre de CO, necessário para aplicações como o abastecimento de células de combustível. Este trabalho de tese teve como objetivo o estudo dos compostos SrTi1-xCuxO3, CuO/SrTiO3 e NiO/SrTiO3 como catalisadores para a reação de deslocamento gás-água, uma vez que, dentre os metais de baixo custo, Cu e Ni são altamente ativos para esta reação. As amostras SrTi1-xCuxO3 foram sintetizadas pelo método dos precursores poliméricos com calcinação em N2 e O2, possibilitando a obtenção de partículas de maior área superficial em comparação com a calcinação convencional em atmosfera ambiente. Para as amostras CuO/SrTiO3 e NiO/SrTiO3, o suporte SrTiO3, foi sintetizado pelo método de sol-precipitação e a impregnação com cobre e níquel foi realizada por via úmida. As técnicas de absorção e difração de raios-X in situ em condições de reação mostraram a estabilidade da estrutura e do estado de oxidação após o tratamento de redução. Imagens de microscopia eletrônica de varredura (MEV) e de transmissão (TEM) em conjunto com a espectroscopia de raios-X de energia dispersiva (EDX) foram utilizadas a fim de estabelecer uma relação entre a atividade catalítica e o teor a dispersão de fase ativa sobre o suporte. Todas as composições estudadas se mostraram ativas entre 250 e 350°C, entretanto, a composição NiO/SrTiO3 com 10% de Ni apresentou o melhor resultado, com uma conversão de CO a 350°C, próxima ao equilíbrio e estável por um período mínimo de10 h. / Strontium titanate (SrTiO3) is an oxide of perovskite structure and has been extensively studied for use in several applications, including as catalytic support. However, its use specifically in the water-gas shift reaction is still little explored. This reaction is of interest for the production of CO-free hydrogen, required for applications such as in fuel cell. This work aimed to study SrTi1-xCuxO3, CuO/SrTiO3 and NiO/SrTiO3 compounds to be applied as catalysts for the water-gas shift reaction, since, among the low-cost metals, Cu and Ni are highly active for this reaction. The SrTi1-xCuxO3 samples were synthesized by the polymeric precursor method with the samples submitted to a N2 and O2 calcination, making possible to obtain particles with a larger surface area compared to conventional calcination in ambient atmosphere. For the CuO/SrTiO3 and NiO/SrTiO3 samples, the SrTiO3 support was synthesized by the sol-precipitation method and the impregnation with copper and nickel on the support was performed by a wet method. The in situ X-ray absorption and diffraction techniques under reaction conditions showed the stability of the structure and the oxidation state after the reduction treatment. Scanning electron microscopy (SEM) and transmission (TEM) images in conjunction with energy dispersive X-ray spectroscopy (EDX) were used in order to establish a relationship between the catalytic activity and the content and dispersion of the active phase on the support. All the compositions studied were active at 250 to 350 °C, however, the NiO/SrTiO3 sample with 10% of Ni presented the best result, with a CO conversion at 350 °C, close to equilibrium and stable for a minimum of 10 h.

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-11T12:50:12Z No. of bitstreams: 2 Tese_Correções_Finais_Banca.pdf: 4119383 bytes, checksum: a96ead41f0aef7ab9bb319e5d0db84cb (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-11T12:50:12Z (GMT). No. of bitstreams: 2 Tese_Correções_Finais_Banca.pdf: 4119383 bytes, checksum: a96ead41f0aef7ab9bb319e5d0db84cb (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-11-22 / CAPES, CTPetro e CNPq / Produção de hidrogênio de elevadas purezas e coprodutos têm sido objeto de desenvolvimentos de tecnologias usando o gás natural como matéria-prima com processamento catalítico como a desidroaromatização (DAM) associada à reforma seca (RSM) em um leito duplo com ocorrência de coprodutos em condições não oxidativas. As produções de hidrogênio previstas objetivam a utilização do monóxido de carbono de efluentes de reformas do gás natural, via reação water gas shift (WGS) e o desenvolvimento de catalisadores avançados de metais preciosos em fases dispersas sobre um suporte. Como objetivo desta pesquisa pode-se citar: i) Desenvolvimento de uma tecnologia usando o gás natural como matéria-prima para produção de hidrogênio de alta pureza, e coprodutos tais como gás de síntese e acetileno como intermediários para formulação de aromáticos, principalmente o benzeno, via desidroaromatização e a reforma seca, em condições não oxidativas, com utilização de reator de leito fixo. ii) Desenvolvimento de novos catalisadores de Pt e Au (formulação e caracterização) e o estudo detalhado dos parâmetros cinéticos, mecanisticos e em diversos suportes e seus efeitos para reação de WGS. Operações de processamento do metano em reator de leito fixo nas condições: 525°C, 550°C, 575°C, 1 atm, 155-180 cm3/min, fração molar Ar :CH4, 0,5:0,5 de metano e argônio para DAM e relação molar Ar :CH4:CO2, 0,57:0,27:0,16 para DAM/RSM. As operações em reator de leito fixo na presença da mistura dos catalisadores (2,60%)Mo-(0,5%)Ru/HZSM e (11,23%)Ni/ -Al2O3, como resultado principal apresentaram uma acentuada produção de acetileno (42,91%) e moderadas produções de hidrogênio e monóxido de carbono (16%-56% H2 e 1,45% CO, 575°C). No processo catalítico de WGS foram estudados catalisadores de platina e ouro em baixas temperaturas (120°C – 300°C) para manter a conversão total de CO nas condições diferenciais abaixo de 10%. O fluxo total de entrada foi mantido constante com uma composição padrão de gás de 6,8% CO, 8,5% CO2, 21,9% H2O e 37,4% H2. A temperatura foi variada numa faixa entre 20° e 30°C, para determinação da energia de ativação aparente. Aplicações de metodologia da cinética de processos catalíticos permitiram estimar valores de baixas energias de ativação (catalisador Pt: 53 kJ/mol – 63 kJ/mol; catalisador Au:11 kJ/mol –95 kJ/mol), os quais confirmaram os bons níveis de atividade dos catalisadores formulados para o processo WGS, com destaque para os catalisadores 2%Pt/TiO2, 2%Au/ZrO2 e 2%Au/TiO2.

Doctor of Philosophy / Department of Chemical Engineering / Bin Liu / Efficient and selective catalysis lies at the heart of many chemical reactions, enabling the synthesis of chemicals and fuels with enormous societal and technological impact. A fundamental understanding of intrinsic catalyst properties for effective manipulation of the reactivity and selectivity of industrial catalysts is essential to select proper catalysts to catalyze the reactions we want and hinder the reactions we do not want. The progress in density functional theory (DFT) makes it possible to describe interfacial catalytic reactions and predict catalytic activities from one catalyst to another. In this study, water-gas shift reaction (WGSR) was used as a model reaction. First-principles based micro-kinetic modeling has been performed to deeply understand interactions between competing reaction mechanisms, and the relationship with various factors such as catalyst materials, structures, promoters, and interactions between intermediates (e.g., CO self-interaction) that govern the observed catalytic behaviors. Overall, in this thesis, all relevant reaction mechanisms in the model reaction on well-defined active sites were developed with first-principles calculations. With the established mechanism, the promotional effect of K adatom on Ni(111) on WGSR compared to the competing methanation was understood. Moreover, the WGSR kinetic trend, with the hydrogen production rate decreasing with increasing Ni particle diameters (due to the decreasing fractions of low-coordinated surface Ni site), was reproduced conveniently from micro-kinetic modeling techniques. Empirical correlations such as Brønsted-Evans-Polanyi (BEP) relationship for O-H, and C-O bond formation or cleavage on Ni(111), Ni(100), and Ni(211) were incorporated to accelerate computational analysis and generate trends on other transition metals (e.g., Cu, Au, Pt). To improve the numerical quality of micro-kinetic modeling, later interactions of main surface reaction intermediates were proven to be critical and incorporated successfully into the kinetic models. Finally, evidence of support playing a role in the enhancement of catalyst activity and the impact on future modeling will be discussed. DFT will be a powerful tool for understanding and even predicting catalyst performance and is shaping our approach to catalysis research. Such molecular-level information obtained from computational methods will undoubtedly guide the design of new catalyst materials with high precision.

The coupling efficiency of carbon nanotubes with near infrared laser radiation at 940nm wavelength was investigated. Nanotubes treated with different post processing methods were irradiated at different laser power intensities as dry samples and suspensions in water or ethanol. The interaction with the laser beam was measured and quantified based on the temperature increase in the samples as well as the amount of energy transmitted through them. Parallel experiments using carbon black revealed better performance of carbon nanotubes in terms of coupling efficiency and heat dissipation to their surroundings. It was found that most of the incident radiation on an individual carbon nanotube is absorbed, resulting in extreme local temperature increases proportional to the laser intensity, which can lead to instant tube oxidation in air. Such high heats are efficiently transferred to the material in immediate contact with the nanotubes, increasing its temperature very rapidly. The most intriguing results were obtained in the presence of water where the observations suggested, disintegration of carbon nanotubes with each laser pulse. It is shown that extremely high local temperatures vaporise the water in the immediate vicinity of a carbon nanotube and result in a water-gas reaction. It is further postulated that such effects can be achieved with laser beams at power intensities near the skin tissue's safe exposure thresholds, and therefore can potentially be used as a method of removing nanotubes from living tissue. This has advantages in providing an exit route for nanotubes whether introduced on purpose for reasons of medicine or therapy, or possibly, as a result of inadvertent exposure. Further studies on laser heating and transmission through different dry samples, highlighted that more crystalline structures such as that of a heat-treated nanotube, are more effective in causing extinction of the laser beam and a reduction in the transmitted beam intensity, however the tubes with more defects or with a length comparable to the radiation wavelength are very effective in converting the absorbed laser energy to heat. This effect is exacerbated when the laser beam is polarised parallel to the long axis of the carbon nanotubes. These heating effects were exploited to create welds in high density polyethylene using through transmission laser welding. The resultant welds showed better than or equal mechanical performance to welds made using industrial absorbers such as carbon black or Clearweld®.

In this research project, adsorption is considered in conjunction with the reverse water gas shift reaction in order to convert CO2 to CO for synthetic fuel production. If the CO2 for this process can be captured from high emitting industries it can be a very good alternative for reduced fossil fuel consumption and GHG emission mitigation. CO as an active gas could be used in Fischer-Tropsch process to produce conventional fuels. Literature review and process simulation were carried out in order to determine the best operating conditions for reverse water gas shift (RWGS) reaction. Increasing CO2 conversion to CO requires CO2/CO separation downstream of the reactor and recycling unreacted CO2 and H2 back into the reactor. Adsorption as a viable and cost effective process for gas separation was chosen for the CO2/CO separation. This was started by a series of adsorbent screening experiments to select the best adsorbent for the application. Screening study was performed by comparing pure gas isotherms for CO2 and CO at different temperatures and pressures. Then experimental isotherm data were modeled by the Temperature-Dependent Toth isotherm model which provided satisfactory fits for these isotherms. Henry law’s constant, isosteric heat of adsorption and binary mixture prediction were determined as well as selectivity for each adsorbent. Finally, the expected working capacity was calculated in order to find the best candidate in terms of adsorption and desorption. Zeolite NaY was selected as the best candidate for CO2/CO separation in adsorption process for this project. In the last step breakthrough experiments were performed to evaluate operating condition and adsorption capacity for real multi component mixture of CO2, CO, H2 in both cases of saturated with water and dry gas basis. In multi components experiments zeolite NaY has shown very good performance to separate CO2/CO at low adsorption pressure and ambient temperature. Also desorption experiment was carried out in order to evaluate the working capacity of the adsorbent for using in industrial scale and eventually temperature swing adsorption (TSA) process worked very well for the regeneration step. Integrated adsorption system downstream of RWGS reactor can enhance the conversion of CO2 to CO in this process significantly resulting to provide synthetic gas for synthetic fuel production as well as GHG emission mitigation.

CuNi nanoparticles were synthesized using a new polyol synthesis method. Three different CuxNi1-x catalysts were synthesized where x = 20, 50 and 80. The nanoparticles were deposited on carbon, C, gamma-alumina, γ-Al2O3, yttria-stabilized zirconia, YSZ, and samariumdoped ceria, SDC. Each set of catalysts was tested using the Reverse Water Gas Shift, RWGS, reaction under atmospheric pressure and at temperatures ranging from 400°C-700°C. The experiments were repeated 3 times to ensure stability and reproducibility. Platinum nanoparticles were also deposited on the same supports and tested for the RWGS reaction at the same conditions. The CuNi nanoparticles were characterized using a variety of different techniques. Xray diffraction, XRD, measurements demonstrate the resence of two CuNi solid solutions: one Cu rich solid solution, and the other a Ni rich solid solution. X-ray photo electron spectroscopy, XPS, measurements show Cu enrichment on all catalytic surfaces. Scanning electron microscopy, SEM, measurements show CuNi nanoparticles ranging in size from 4 nm to 100 nm. Some agglomeration was observed. SDC showed the best yield with all catalysts. Furthermore, high oxygen vacancy content was shown to increase yield of CO for the RWGS reaction. Cu50Ni50/SDC shows the combination of highest yield of CO and the best stability among CuNi catalysts. It also has similar yields (39.8%) as Pt/SDC at 700°C, which achieved the equilibrium yield at that temperature (43.9%). The catalyst was stable for 48 hours when exposed to high temperatures (600-700°C). There was no CH4 observed during any of the experiments when the partial pressure of the reactant gases was fed stoichiometrically. Partial pressure variation experiments demonstrated the presence of CH4 when the partial pressure of hydrogen was increased to twice the value of the partial pressure of CO2.

In this research project, adsorption is considered for the separation of CO2 from CO for applications such as industrial syngas production and in particular to improve the conversion of the Reverse Water Gas Shift (RWGS) process. The use of adsorption technology for these applications requires an adsorbent that can effectively separate out CO2 from a gas mixture containing CO2, CO, and H2. However, adsorption of H2 is insignificant when compared to both CO2 and CO, with only CO2 and CO being the adsorbed species. The adsorption of CO2 and CO was investigated in this work for four major types of industrial adsorbents which include: activated aluminas, activated carbons, silica gels, and zeolites. Zeolites, with their ability to be fine tuned many parameters which may affect adsorption, were investigated in terms of the effect of the cations present, SiO2/Al2O3 ratios, and structure to determine how to optimize adsorption of CO2 while decreasing adsorption of CO. This will help to determine a promising adsorbent for this separation with focus on maximizing the selective adsorption of CO2 over CO. To investigate this separation three scientific experimental methods were used; gravimetric adsorption isotherm analysis, volumetric adsorption isotherm analysis, and packed bed adsorption desorption breakthrough analysis. Gravimetric and volumetric methods allow for testing the adsorbent with the individual species of CO2 and CO. This investigation will let us determine the pure component adsorption capacity, heats of adsorption, regenerability, and basic selectivity. Packed bed adsorption breakthrough experimentation was then carried out on promising adsorbents for the CO2 separation from a mixture of CO2, CO, and H2. These experiments used a gas mixture that would be comparable to that produced from the RWGS reaction to determine the multicomponent gas mixture behaviour for adsorption. Temperature swing adsorption (TSA) with a purge gas stream of H2 was then used to regenerate the adsorbent.

Since the industrial evolution, the CO2-levels have been increasing in a way that’s never seen in the history of the earth. To mitigate and adapt to the happening climate change it is really important to understand the global carbon cycle and each component that plays a role in it. Some studies suggest that there has been an underestimation on the influence from inland waters in the total carbon budget.To address this issue, there has been Eddy Covariance measurements going on the boreal Indalsälven river in front of the Kattstrupeforsen water dam. In this study continuous data has been collected which includes air-river CO2-flux, pCO2-values in the air and the water and some more meteorological parameters such as the wind speed, relative humidity and the air and water temperature. The aim of this study is to look into the seasonal variation in pCO2-levels and the CO2-fluxes on the Indalsälven river.The data indicates that the CO2-fluxes are mainly positive from January till July (average flux = 0.2 μmol m-2s-1) and mainly negative from September till November (average flux = -0.59 μmol m-2s-1) with an average flux of 0.212 μmol m-2s-1 during 2019. The main range of CO2-fluxes per month lies between -2 and 2 μmol m-2s-1, with the exception of March and December where there is a bigger range of fluxes. The pCO2-levels in the water mainly range between 400 and 1000 ppm. With the exception of 2 periods, one in the end of May where there is a peak to 4000ppm and more which can be explained by the spring flood and in the end of July and beginning of August where there is a peak to 3000 ppm. / <p>2020-06-17</p>