Made available in DSpace on 2016-06-02T19:56:45Z (GMT). No. of bitstreams: 1 3936.pdf: 2010584 bytes, checksum: 3be708f515e15835c7915065004f5f86 (MD5) Previous issue date: 2011-10-27 / The minimization of emissions of nitrogen oxides (NOx) is a subject of great interest because they cause serious environmental problems affecting human health, flora and fauna. To break down the NOx catalytic reduction of these compounds to N2 has acquired great importance and may occur in the absence or presence of a reducing agent. The selective catalytic reduction using ammonia as a reducing agent (NH3-SCR) has been shown to be one of the most attractive, being used worldwide to control NOx emissions by industries due to its high efficiency, selectivity and low cost. To obtain more efficient catalysts for this reaction, several studies have been developed. In this context, the objective of this work is to prepare, to wet impregnation, catalysts based on vanadium, molybdenum and iron supported on commercial TiO2 and lamellar titanates (TL) with high (A-TL) or low-sodium (B-TL), and apply them to the reduction of NO with NH3.It was also studied the effect of calcination temperature in titanates with low sodium content. Results of XRD and adsorption of N2 measurements confirmed the formation of TL mesoporous structure and high specific surface area. After the addition of metal to TiO2 and TL, it was observed a significant decrease in the values of specific surface areas, attributed to the filling of pores by metal oxides. The RTP-H2 showed lower reducibility of metals supported on the lamellar titanates and commercial TiO2 support. The catalysts supported TL with high sodium content showed lower catalytic activity compared to commercial catalysts . However, the catalysts supported on titanates with low sodium content showed promising results in the conversion of NO to N2. The catalysts Fe2O3/TiO2 Fe2O3/B-TL showed loss of activity in the presence of SO2, which partially regenerates in the absence of the compound. In the presence of water, both catalysts showed a decline in the conversion, With the removal of H2O the Fe2O3/TiO2 showed partial regeneration, while the Fe2O3/B-TL suffered irreversible deactivation. / A minimização das emissões de óxidos de nitrogênio (NOx) é assunto de alto interesse pois causam graves problemas ambientais afetando a saúde humana, à flora e à fauna. Para abater os NOx, a redução catalítica desses compostos a N2 vem adquirindo grande relevância, podendo ocorrer na ausência ou presença de um agente redutor. A redução catalítica seletiva utilizando amônia como agente redutor (RCS-NH3) tem-se mostrado um dos processos mais atrativos, sendo mundialmente aplicado no controle de emissão do NOx pelas indústrias, devido a sua alta eficiência, seletividade e baixo custo. Para a obtenção de catalisadores mais eficientes para essa reação, diversos estudos tem sido desenvolvidos. Nesse contexto, o objetivo deste trabalho é preparar, via impregnação úmida, catalisadores à base de vanádio, molibdênio e ferro suportados em TiO2 comercial e titanatos lamelares (TL) com alto (A-TL) ou (B-TL) baixo teor de sódio, e aplicá-los na redução de NO com NH3. Foi verificado estudado também o efeito da temperatura de calcinação nos titanatos com baixo teor de sódio. Resultados de DRX e medidas de adsorção de N2 confirmaram a formação de TL de estrutura mesoporosa e de alta área superficial específica. Após a adição dos metais aos suportes TiO2 e TL, foi observada uma queda significativa nos valores das áreas superficiais específicas, atribuída ao preenchimento dos poros pelos óxidos metálicos. O RTP-H2 indicou menor redutibilidade dos metais suportados nos titanatos lamelares frente ao suporte TiO2 comercial. Os catalisadores suportados em TL com alto teor de sódio apresentaram atividade catalítica inferior quando comparados aos catalisadores suportados em TiO2 comercial. No entanto, os catalisadores suportados nos titanatos com baixo teor de sódio apresentaram resultados promissores na conversão do NO a N2. Os catalisadores Fe2O3/TiO2 e Fe2O3/B-TL registraram queda parcial na atividade quando na presença do SO2, que se regenera parcialmente na ausência do composto. Na presença de água, ambos catalisadores apresentaram queda na conversão, sendo que, na retirada deste composto, o Fe2O3/TiO2 apresentou parcial regeneração, ao passo que, o Fe2O3/B-TL, sofreu desativação irreversível.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.

In the last few decades India has advanced socioeconomically due to the rapid growth of industries and automobile sector. This in turn increases the use of fossil fuel and diesel. The atmosphere gets polluted due to the harmful substances, which comes from the burning of fuel. These pollutants can be in the form of gaseous, liquid or solid particulate. Diesel engines, the major source of power in industries and automobiles, play a significant part in causing air pollution. The major pollutants in diesel exhaust are oxides of nitrogen (NOX), sulphur dioxide (SO2), carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), volatile organic compounds (VOC), aldehydes and alcohols. Due to the heavy consumption of diesel as a fuel there is an urgent need to control diesel exhaust. Diesel exhaust is a complex mixture of several gases and fine particles (commonly known as soot) that contains more than 40 toxic air contaminants. Amongst the gaseous pollutants in diesel exhaust, the major concern and a challenging task is to control oxides of nitrogen, commonly referred to as NOX as it is the major contributor for acid rain, photochemical smog etc. Successful control of emissions from diesel engines is yet to be achieved. The conventional techniques which are available to control emission now are either difficult to operate or does not satisfy the stringent emission standards. This has made the researchers throughout the world to find an alternative and effective non-conventional after treatment technique to reduce diesel engine emission. The failure of conventional techniques lead to the development of non-conventional techniques such as high voltage electric discharge based plasma which has already been proved to be economical and highly efficient in industrial electrostatic precipitators. Electric discharge plasma or non-thermal plasma produce energetic electrons which react with background molecules in flue gas leading to active species such as radicals. These radicals being chemically active selectively react with the harmful pollutants facilitating their removal/reduction. The present thesis work is an attempt to provide a technical solution to achieve higher removal efficiencies of oxides of nitrogen in the backdrop of shortcomings that exist in conventional technologies to do so. The current thesis describes the research in four stages: (i) studies on NOX removal from diesel exhaust by cross-flow DBD reactor, where design and fabrication of cross-flow DBD reactor, exhaust treatment using cross-flow DBD reactor and exhaust treatment with cascaded plasma-adsorbent technique is described (ii) studies on NOX removal from diesel exhaust by compact discharge plasma sources, where design and fabrication of high frequency high voltage AC (HVAC) using old television flyback transformer, Design and fabrication of high voltage pulse (HVPulse) using automobile ignition coil, exhaust treatment with both HVPulse and HVAC and exhaust treatment with cascaded plasma-adsorbent technique is described (iii) studies on NOX removal from diesel exhaust using solar powered discharge plasma source is described (iv) studies on the NOX removal from diesel exhaust using red mud, where exhaust treatment with red mud and Exhaust treatment cascaded plasma-red mud is covered. The results have been discussed in light of enhancing the NOX removal efficiency for stationary and automobile engine exhausts.