The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.

The reaction mechanism for the Selective Catalytic Reduction (SCR) of NO by NH3 on V2O5 surface was simulated by means of density functional theory (DFT) calculations performed at B3LYP/6-31G** level. As the initiation reaction, ammonia activation on V2O5 was investigated. Coordinate driving calculations showed that ammonia is adsorbed on Br&oslash / nsted acidic V-OH site as NH4 + species by a nonactivated process with a relative energy of -23.6kcal/mol. Vibration frequencies were calculated as 1421, 1650, 2857 and 2900cm-1 for the optimized geometry, in agreement with the experimental literature. Transition state with a relative energy of -17.1kcal/mol was also obtained. At the end of the Lewis acidic ammonia interaction calculations, it was observed that ammonia is hardly adsorbed on the surface. Therefore, it is concluded that the SCR reaction is initiated more favorably by the Br&oslash / nsted acidic ammonia adsorption. As the second step of the SCR reaction, NO interaction with the preadsorbed NH4 + species was investigated. Accordingly, NO interaction results in the formation of gas phase NH2NO molecule with a relative energy difference of 6.4kcal/mol. For the rest of the reaction sequence, gas phase decomposition of NH2NO was considered. Firstly, one of the hydrogen atoms of NH2NO migrates to oxygen. It then isomerizes in the second step. After that, the reaction proceeds with the isomerization of the other hydrogen. Finally, a second hydrogen atom migration to the oxygen leads to the formation of N2 and H2O. Total relative energy for this reaction series was obtained as -60.12kcal/mol, in agreement with the literature.

With increasing legislative demands to remove nitrogen oxides (NOx) from automotive diesel exhaust, new catalyst systems are investigated and intensely studied in industry as well in academia. The most prevailing catalytic method of choice is the selective catalytic reduction (SCR) where non-toxic urea is used as a reductant for practical reasons. Usually urea is stored in a separate tank and once injected into the exhaust system it hydrolyses into the more aggressive reductant NH3 and CO2. 4 NH3 + 4 NO + O2 -> 4 N2 + 6 H2O (NH3-SCR reaction) In regions where vanadium is not banned cost effective V2O5/WO3/TiO2 NH3-SCR catalyst systems can be used. Vanadium based are well understood, but they do however not provide stability above ca. 550 °C for longer periods of time. In exhaust treatment systems where the temperature is either high or where high temperature excursions are experienced from e.g. regeneration of particulate filters, zeolite based catalysts are therefore today the most promising candidates as high-temperature stable and non-toxic catalysts for the NH3-SCR reaction. Among the most promising candidates are the Cu- and Fe-based zeolites. Usually Fe based zeolites show good performance in the temperature range 250-500 °C and reasonable stability, whereas Cu-based zeolites show good low-temperature activity in the 180-400 °C range. The presence of copper does however also lead to a lower stability of the catalyst material. Since the low-temperature activity is of paramount importance it is necessary to improve this behavior. Therefore the purpose of this project is to investigate: - The deactivation mechanism of copper based zeolites - The influence of the zeolite framework on stability and activity These investigations should mostly be carried out on model systems such as Cu-ZSM-5 and Cu-IM-5. Recently it was found that zeolite materials with the CHA-type structure show increased hydrothermal stability, most likely originating from the small 8-MR window openings in the structure. Part of the project should therefore also include investigations on this type and other similar structures, and therefore entail: - Synthesis, in-depth characterization and catalytic testing of Cu-SSZ-13 and Cu-SAPO-34 (both structures having the CHA-type framework) - Theoretical DFT calculations on relevant parameters found by the in-depth investigation of the afore-mentioned materials - Synthesis and testing of similar materials with 8-MR windows to elucidate the influence of the zeolite sub-structure i.e. if different ring sizes in the structure influences the catalytic performance Relevant characterization techniques include, besides conventional methods, in situ methods such as: high resolution (transmission) electron microscopy, infrared (and raman) spectroscopy together with X-ray absorption spectroscopy. These are all techniques that will complement each other to produce invaluable results. Zeolites are today applied in many and diverse applications both within automotive and environmental catalysis, but also within the petrochemical and renewable chemistry. The findings of this project are therefore also believed to contribute to a more comprehensive understanding of this class of materials, relevant to many areas of heterogeneous catalysis, and therefore have the potential, to create research and business with very high impact. / Vennestrom, PNR. (2014). Selective catalytic reduction of nitrogen oxides with ammonia over microporous zeolite catalysts [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43217 / TESIS

This diploma thesis deals with the issue of nitrogen oxides emissions in exhaust gases and possibilities of their reduction. The task of the thesis was analysis of systems for NOX reduction by contemporary diesel engines, design and construction of NOX reduction device for given diesel engine, then verify functionality of this system compiled from commercially available components. In the last part of thesis available measurements will be made with an analysis of achieved results.

The diploma thesis is focused on experimental reduction of nitrogen oxides on special catalysts. The latest and state-of-the-art flue gas cleaning technologies are used. Selective catalytic reduction results in the desired level of pollution. It is necessary to meet the prescribed emission limit. A ceramic honeycomb filter based on vanadium and titanium is used as the catalyst. The entire measurement is carried out on the experimental INTEQ II unit, which is installed in the flue gas cleaning laboratory at NETME Center. It is shown which operating parameters achieve better efficiency of flue gas cleaning. Comparison of the BASF and CERAM catalysts is also performed. Finally, a material balance of the system is performed and a new external electric heater is designed to accelerate the heating process.

There is an overview of secondary methods for NOX removal from stationary sources in the first part of master’s thesis. There are well known methods as SCR o SNCR, but also new and experimental ones. An accent is putting on catalytic filtration, especially on cloth filter, which will be used for experiments. An important part of master’s thesis is a project of new experimental unit for experiments with cloth and ceramic catalytic filters as well as with a bit of cloth filtration material. Unit has compact proportions, high-class measurement and control and wide application spectra. Other advantages of this equipment are fast and easy cleaning and installation. This unit, called INTEQ II, can be used in plants or in laboratories. There is prediction model created together with new technology. It enables calculation of efficiency at catalytic filters with variable conditions without many experiments. This model is elaborate and will be finished with dates from measuring. There in only summary of planned experiments in this thesis, because measurements at new unit have not done yet. Experiences with operations at unit INTEQ I were used for proposal of new equipment and for experiments planning.

Research in the field of NOX abatement has grown significantly in the past two decades. The general trend has been to develop new catalysts with complex materials in order to meet the stringent environmental regulations. The master’s thesis deals with the cleaning flue gases through a filter element which is from porous ceramics. There is catalyst implemented for NOx reduction throug the method of selective catalytic reduction in the filter element. There is also description of experimental unit for flue gas cleaning. Part of the thesis is creation of prediction model which allows to predict efficiency reduction in the filtration device operating conditions with some accuracy.

<p>Zeolites contain distinct Brønsted acid site (H⁺) ensembles that arise from differences in the arrangement of framework Al atoms (Al−O(−Si−O)x−Al) between isolated (x ≥3) and paired (x=1,2) configurations, the latter defined by their ability to exchange certain divalent cations (e.g., Cu²⁺, Co²⁺). Manipulation of the synthesis conditions used to prepare MFI zeolites has been proposed to influence the proximity of framework Al atoms, but in a manner that is neither determined randomly nor by any simple predictive rules. Moreover, the effects of proton proximity have been studied for hydrocarbon catalysis in MFI zeolites, but interpretations of catalytic phenomena are convoluted by effects of the distribution of framework Al atoms among different crystallographic tetrahedral sites (T-sites) and diverse pore environments (i.e., confining environments) present in MFI. This work instead focuses on the chabazite (CHA) framework, which contains a single crystallographically-distinct lattice tetrahedral site (T-site) that allows clarifying how synthesis conditions influence Al proximity, and in turn, how H⁺ site proximity influences catalysis independent of T-site location. </p> <p> Selective quantification of the number and type of H⁺ site ensembles present in a given zeolite allows for more rigorous normalization of reaction rates by the number of active sites, but also for probing the number and identity of active sites on bifunctional catalysts that contain mixtures of Brønsted and Lewis acid sites. Gaseous NH₃ titrations can be used to count the total number of protons on small-pore CHA zeolites, which are inaccessible to larger amine titrants (e.g., pyridine, alkylamines), and can be used to quantify the exchange stoichiometry of extraframework metal cations (e.g., Cu²⁺, [CuOH]⁺) that are stabilized at different framework Al arrangements. Additionally, paired Al sites in CHA zeolites can be titrated selectively by divalent Co²⁺ cations, whose sole presence is validated by measuring UV-Visible spectra, counting residual protons after Co²⁺ exchange, and titration of paired Al with other divalent cations (e.g., Cu²⁺). These different titration procedures enabled reliable and reproducible quantification of different Al arrangements, and recognition of the effects of different synthetic methods on the resulting arrangement of framework Al atoms in CHA zeolites. </p> <p>Upon the advent of this suite of characterization and titration tools, different synthetic methods were developed to crystallize CHA zeolites at constant composition (e.g., Si/Al = 15) but with systematic variation in their paired Al content. The substitution of N,N,N-trimethyl-1-adamantylammonium (TMAda⁺) cations for Na⁺ in the synthesis media (Na⁺/TMAda⁺<2), while holding all other synthetic variables constant, resulted in CHA zeolites of similar composition (Si/Al = 15) and organic content (ca. 1 TMAda⁺ per cage), but with percentages of paired Al (0-44%) that increased with the total amount of sodium retained on the zeolite product. This result suggests that sodium atoms are occluded near the ammonium group of TMAda⁺ leading to the formation of a paired Al site. Replacement of Na⁺ by other alkali cations in the synthesis media allowed for the crystallization of CHA (Si/Al = 15) at higher ratios of alkali to TMAda⁺than accessible by Na⁺, likely due to the ability of different alkali cations to favor (or inhibit) crystallization of other zeolite phases. Incorporation of different alkali cations during CHA crystallization influences the formation of paired Al sites in different ways, likely reflecting the nature of different alkali to preferentially occupy different positions within the CHA framework. <i>Ab initio</i> molecular dynamics simulations were used to assess the stability of various Al-Al arrangements in the presence of combinations of alkali and TMAda⁺ cations, and provide thermodynamic insight into electrostatic interactions between cationic structure-directing agents that stabilize paired Al sites in CHA. </p> <p> Using these synthetic procedures to prepare CHA zeolites of similar composition, but with varied arrangements of framework Al, the catalytic consequences of framework Al arrangement were investigated using acid and redox catalysis. The low-temperature (473 K) selective catalytic reduction of NOx with NH₃ (NH₃-SCR) was investigated over Cu-exchanged CHA zeolites containing various Al arrangements. Cu cations exchange as both divalent Cu²⁺ and monovalent [CuOH]⁺ complexes, which exchange at paired and isolated Al sites, respectively, and turnover with similar SCR rates (473 K). <i>In situ</i> and <i>operando</i> X-ray absorption spectroscopy (XAS) were used to monitor the oxidation state and coordination environment of Cu as a function of time and environmental conditions. Rationalization of these experimental observations by first-principles thermodynamics and <i>ab initio</i> molecular dynamics simulations revealed that both Cu²⁺ and [CuOH]⁺ complexes are solvated by NH₃ and undergo reduction to Cu⁺ upon oxidation of NO with NH₃. Cu⁺ cations become mobilized by coordination with NH₃ under reaction conditions (473 K, equimolar NO and NH₃ feed), and activate O₂ through a dicopper complex formed dynamically during reaction. These results implicate the spatial density of nominally site-isolated Cu cations and, in turn, the arrangement of anionic framework Al atoms that anchor such cationic Cu complexes, influence the kinetics of O₂ activation in selective oxidation reactions, manifested as SCR rates (per 1000 A³) that depend quadratically on Cu density (per 1000 A³) and become rate-limiting processes in practice at low temperatures.</p> <p>Furthermore, first-order and zero-order rate constants (415 K, per H⁺) of methanol dehydration, a probe reaction of acid strength and confinement effects in solid Brønsted acids, are nearly one order of magnitude larger on paired than on isolated protons in CHA zeolites, reflecting differences in prevalent mechanisms and apparent enthalpic and entropic barriers at these different active site ensembles. Yet, these differences in rate constants and activation parameters at isolated and paired protons do not persist within larger pore zeolites (e.g., MFI). <i>In situ </i>IR spectra measured during steady-state methanol dehydration catalysis (415 K, 0.05-22 kPa CH₃OH) reveal that surface methoxy species are present in CHA zeolites containing paired protons, but not in CHA zeolites containing only isolated protons or MFI zeolites, providing evidence that sequential dehydration pathways via methoxy intermediates become accessible on paired protons in CHA. Density functional theory is used to provide atomistic detail of confined intermediates and transition states at isolated and paired protons in CHA and MFI zeolites, indicating that paired protons in CHA preferentially stabilize dehydration transition states that are partially-confined within the 8-membered ring (8-MR) of CHA. These findings provide evidence that catalytic diversity for the same stoichiometric reaction among zeolites of fixed structure and composition, even for frameworks containing a single T-site, can be introduced deliberately through synthetic control of the atomic arrangement of matter. </p>

The need for sustainability has been on the rise. Municipalities are finding ways of reducing waste, but also finding ways to reduce energy costs. Waste-to-energy is a sustainable method that may reduce bio-solids volume while also producing energy. In this research study bio-solids enters a bubbling bed gasifier and within the gasifier a synthesis gas is produced. This synthesis gas exits through the top of the gasifier and enters a thermal oxidizer for combustion. The thermal oxidizer has an innovative method of oxidizing the synthesis gas. The thermal oxidizer has two air injection sites and the possibility for aqueous ammonia injection for further NOx reduction. Most thermal oxidizers already include an oxidizer such as air in the fuel before it enters the thermal oxidizer; thus making this research and operation different from many other thermal oxidizers and waste-to-energy plants. The reduction in waste means less volume loads to a landfill. This process significantly reduces the amount of bio-solids to a landfill. The energy produced from the synthesis is beneficial for any municipality, as it may be used to run the waste-to-energy facility. The purpose of this study is to determine methods in which operators may configure future plants to reduce NOx emissions. NOx mixed with volatile organic compounds (VOC) and sunlight, produce ozone (O3) a deadly gas at high concentrations. This study developed a model to determine the best methods to reduce NOx emissions. Results indicate that a fuel-rich then fuel-lean injection scheme results in lower NOx emissions. This is because at fuel-rich conditions not all of the ammonia in the first air ring is converted to NOx, but rather a partial of the ammonia is converted to NOx and N2 and then the second air ring operates at fuel-lean which further oxidizes the remaining ammonia which converts to NOx, but also a fraction to N2. If NOx standards reach more stringency then aqueous ammonia injection is a recommended method for NOx reduction; this method is also known as selective non-catalytic reduction (SNCR). The findings in this study will allow operators to make better judgment in the way that they operate a two air injection scheme thermal oxidizer. The goal of the operator and the organization is to meet air quality standards and this study aims at finding ways to reduce emissions, specifically NOx.

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