Добірка наукової літератури з теми "Low-temperature catalytical oxidation"

Volatile organic compounds (VOCs) are organic chemicals mostly emitted from different sources like industrial or domestic having high vapor pressure at room-temperature conditions. Some of these are also anthropogenic in nature and also these are the major contributor for the photochemical ozone. The different methods available for the abatement of VOCs are thermal oxidation, catalytic oxidation, photocatalytic oxidation, adsorption etc. Due to the stringent regulation of VOCs emission in different countries there is a need of efficient abatement technology to preserve the environment. In this context catalytic combustion of organic pollutants offers considerable advantages over the industrially operated thermal combustion process. Generally, oxidative destruction is possible at low temperature in presence of a catalyst. In addition catalytic process is more energy efficient and can operate with very dilute pollutants. A number of catalysts have been used for the complete oxidation of VOCs, among these Pillared clays type porous materials are also useful for the purpose. Pillared clays have high surface area, pore volume, thermal stability and can be tailor made for particular catalytic application compared with the parent clays. In the present review we will summarize the latest developments on the clay based materials including the effect of different controlling parameters for the synthesis of pillared clay based porous materials and its specific application for the low temperature VOCs decomposition. In particular the effect of transition metals like iron and manganese oxide pillared clay on the VOC decomposition is discussed.

Metal nanoparticles (NPs) have received much attention for potential applications in medicine (mainly in oncology, radiology and infectiology), due to their intriguing chemical, electronical, catalytical, and optical properties such as surface plasmon resonance (SPR) effect. They also offer ease in controlled synthesis and surface modification (e.g., tailored properties conferred by capping/protecting agents including N-, P-, COOH-, SH-containing molecules and polymers such as thiol, disulfide, ammonium, amine, and multidentate carboxylate), which allows (i) tuning their size and shape (e.g., star-shaped and/or branched) (ii) improving their stability, monodispersity, chemical miscibility, and activity, (iii) avoiding their aggregation and oxidation over time, (iv) increasing their yield and purity. The bottom-up approach, where the metal ions are reduced in the NPs grown in the presence of capping ligands, has been widely used compared to the top-down approach. Besides the physical and chemical synthesis methods, the biological method is gaining much consideration. Indeed, several drawbacks have been reported for the synthesis of NPs via physical (e.g., irradiation, ultrasonication) and chemical (e.g., electrochemisty, reduction by chemicals such as trisodium citrate or ascorbic acid) methods (e.g., cost, and/ortoxicity due to use of hazardous solvents, low production rate, use of huge amount of energy). However, (organic or inorganic) eco-friendly NPs synthesis exhibits a sustainable, safe, and economical solution. Thereby, a relatively new trend for fast and valuable NPs synthesis from (live or dead) algae (i.e., microalgae, macroalgae and cyanobacteria) has been observed, especially because of its massive presence on the Earth’s crust and their unique properties (e.g., capacity to accumulate and reduce metallic ions, fast propagation). This article discusses the algal-mediated synthesis methods (either intracellularly or extracellularly) of inorganic NPs with special emphasis on the noblest metals, i.e., silver (Ag)- and gold (Au)-derived NPs. The key factors (e.g., pH, temperature, reaction time) that affect their biosynthesis process, stability, size, and shape are highlighted. Eventually, underlying molecular mechanisms, nanotoxicity and examples of major biomedical applications of these algal-derived NPs are presented.

Novel oxidation technology to decolorize dye wastewater was discussed and the feasibility of color removal with Fe/MgO catalyst fluidizing in a reactor under continuous flow was demonstrated at room temperature. In batch tests, the oxidation reaction of reactive and disperse dye with an oxidizing agent, hydrogen peroxide, in the presence of Fe/MgO catalyst was performed. Through the catalytic oxidation, dyes were oxidized to molecules with lower molecular weight and then mineralized based on TOC analysis. The influence of hydrogen peroxide and catalyst dosage on the catalytic oxidation rate was verified. The catalytic oxidation rate increased with increasing hydrogen peroxide and catalyst dosage. Fe/MgO catalyst fluidizing in the reactor operated at room temperature was tested to decolorize the wastewater from a dye manufacturing industry. In the fluidized bed reactor, the wastewater was completely decolorized and about 30% of COD removal was obtained during 30 days of operation. Organic matters were degraded and part of them mineralized by the catalytic oxidation. BOD/COD ratio of the effluent from the fluidized bed reactor was increased compared to that of the influent. After 30 days of operation, the effluent from the fluidized bed reactor started becoming yellowish. COD and residual hydrogen peroxide concentration in the effluent started to increase due to the catalyst losing its activity.

Manganese oxide catalysts, including γ-MnO2, Mn2O3 and Mn3O4, were synthesized by a precipitation method using different precipitants and calcination temperatures. The catalytic oxidations of benzene and 1,2-dichloroethane (1,2-DCE) were then carried out. The effects of the calcination temperature on the catalyst morphology and activity were investigated. It was found that the specific surface area and reducibility of the catalysts decreased with the increase in the calcination temperature, and both the γ-MnO2 and Mn3O4 were converted to Mn2O3. These catalysts showed good activity and selectivity for the benzene and 1,2-DCE oxidation. The γ-MnO2 exhibited the highest activity, followed by the Mn2O3 and Mn3O4. The high activity could be associated with the large specific surface area, abundant surface oxygen species and excellent low-temperature reducibility. Additionally, the catalysts were inevitably chlorinated during the 1,2-DCE oxidation, and a decrease in the catalytic activity was observed. It suggested that a higher reaction temperature could facilitate the removal of the chlorine species. However, the reduction of the catalytic reaction interface was irreversible.

The main goal of the study was the development of effective catalysts for the low-temperature selective catalytic reduction of NO with ammonia (NH3-SCR), based on ferrierite (FER) and its delaminated (ITQ-6) and silica-intercalated (ITQ-36) forms modified with copper. The copper exchange zeolitic samples, with the intended framework Si/Al ratio of 30 and 50, were synthetized and characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low-temperature N2 adsorption), form and aggregation of deposited copper species (UV-vis-DRS), surface acidity (NH3-TPD) and reducibility (H2-TPR). The samples of the Cu-ITQ-6 and Cu-ITQ-36 series were found to be significantly more active NH3-SCR catalysts compared to Cu-FER. The activity of these catalysts in low-temperature NH3-SCR was assigned to the significant contribution of highly dispersed copper species (monomeric cations and small oligomeric species) catalytically active in the oxidation of NO to NO2, which is necessary for fast-SCR. The zeolitic catalysts, with the higher framework alumina content, were more effective in high-temperature NH3-SCR due to their limited catalytic activity in the side reaction of ammonia oxidation.

Catalytic oxidation of organic volatile compounds (VOCs) is considered superior to conventional methods because very low concentration of VOCs can also be oxidized and removed at low temperatures without consumption of addditional fuel and introduction of NOx compounds into the environment. Herein, the synthesis of MnO2 nanoparticles on bentonite (Bent) support in the presence of CuO for catalytic oxidation of m-xylene is reported. The synthesized materials were analyzed with FT-IR, XRD, and TEM analysis for structural and morphological characterization. XRD and TEM analysis indicated the formation of δ-MnO2 with sheet structure on Bent surface. Temperature-programmed reduction (H2-TPR) of hydrogen was used to investigate catalytic performance of δ-MnO2 towards oxidation of m-xylene at different temperatures. The catalytic activity was strongly dependent on the δ-MnO2 content in the synthesized material. 100 % oxidation of m-xylene with observed with 10% Mn content at temperature below than 325 oC. Intersetingly introduction of CuO greatly improved the catalytic activity of Mn-Bent materials. The presence of Cu in Mn-Bent has greatly reduced the temperature for complete oxidation of m-xylene. In this case100% conversion of m-xylene was observed at 250 oC.

Catalytic oxidation of organic volatile compounds (VOCs) is considered superior to conventional methods because very low concentration of VOCs can also be oxidized and removed at low temperatures without consumption of addditional fuel and introduction of NOx compounds into the environment. Herein, the synthesis of MnO2 nanoparticles on bentonite (Bent) support in the presence of CuO for catalytic oxidation of m-xylene is reported. The synthesized materials were analyzed with FT-IR, XRD, and TEM analysis for structural and morphological characterization. XRD and TEM analysis indicated the formation of δ-MnO2 with sheet structure on Bent surface. Temperature-programmed reduction (H2-TPR) of hydrogen was used to investigate catalytic performance of δ-MnO2 towards oxidation of m-xylene at different temperatures. The catalytic activity was strongly dependent on the δ-MnO2 content in the synthesized material. 100 % oxidation of m-xylene with observed with 10% Mn content at temperature below than 325 oC. Intersetingly introduction of CuO greatly improved the catalytic activity of Mn-Bent materials. The presence of Cu in Mn-Bent has greatly reduced the temperature for complete oxidation of m-xylene. In this case100% conversion of m-xylene was observed at 250 oC.

Low temperature (165°C) Wet Oxidation (WO) and Catalytic Wet Oxidation (CWO) of 12 organic compounds has been studied in highly alkaline, high ionic strength solution (simulating that encountered in the Bayer process used to refine alumina) for the first time. Most (11 out of 12) of the 12 organic compounds studied (formic, acetic, propionic, butyric, oxalic, malonic, succinic, glutaric, citric, lactic, malic and tartaric acids) have been identified in various worldwide Bayer liquors. The various aspects of WO and CWO studied for each of the above-mentioned compounds were as follows; -Extent of complete oxidation to carbonate (i.e. extent of removal of organic compound) -Extent of overall oxidation (i.e. extent of complete oxidation and partial oxidation to stable products) -The product(s) formed from partial (incomplete) oxidation -The reaction mechanism occurring -Why certain compounds undergo low temperature WO and/or CWO in highly alkaline, high ionic strength solution -The ability of various transition metal oxides to catalyse the WO of the selected organic compounds Of the 12 organic compounds studied only six (formic, malonic, citric, lactic, malic and tartaric acids) underwent appreciable (>2% overall oxidation) WO in isolation under the reaction conditions used (4.4 -7.0 M NaOH, 165°C, 500 kPa Po₂, 2 hours). Each of these six compounds underwent some complete oxidation and therefore can be partly removed from highly alkaline, high ionic strength solution using low temperature WO. The order of extent of complete oxidation determined was as follows tartaric> citric> malonic> formic> lactic> malic. All of these compounds also underwent some partial oxidation under the reaction conditions used, excluding formic acid, which only underwent complete oxidation. Oxalic acid was a major product of partial oxidation of all of the above-mentioned compounds (excluding formic acid), while acetic acid was a major product of partial oxidation of citric, lactic, malic and tartaric acids. The WO of formic, malonic, citric, lactic, malic and tartaric acids varied considerably with NaOH concentration over the NaOH concentration range studied (4.4 - 7.0 M). The extent of overall oxidation undergone by each of these compounds increased significantly with increasing NaOH concentration. All of the compounds that underwent appreciable WO under the reaction conditions studied contained hydrogen(s) significantly more acidic then the compounds that did not undergo appreciable WO, thus indicating that only organic compounds that contain acidic (albeit weakly acidic) hydrogens undergo low temperature (165°C) WO in highly alkaline, high ionic strength solution. Two different reaction mechanisms were identified to occur during low temperature WO in highly alkaline, high ionic strength solution. Malonic and formic acids underwent WO predominantly via a free radical based reaction mechanism, while citric, lactic, malic and tartaric acids underwent WO predominantly via an ionic based reaction mechanism. The six organic compounds that did not undergo appreciable WO in isolation (acetic, propionic, butyric, oxalic, succinic and glutaric acids) all underwent appreciable WO when in the presence of malonic acid undergoing low temperature WO. Hence, low temperature WO of all of the above-mentioned compounds can be initiated by free radical intermediates produced by malonic acid undergoing WO in highly alkaline, high ionic strength solution. The ability of several transition metal oxides to catalyse the WO of the chosen 12 organic compounds was investigated. Of the transition metal oxides studied CuO was clearly the most active. Five of the organic compounds studied (malonic, citric, lactic, malic and tartaric acids) were catalytically wet oxidised by CuO in highly alkaline, high ionic strength solution in isolation. The order of catalytic activity observed was malonic > tartaric> lactic> malic> citric. Two different catalytic reaction mechanisms were identified for CuO catalysed WO in highly alkaline solution for the organic compounds studied. CuO catalysed the WO of malonic acid predominantly by catalysing the formation of free radical intermediates. CuO catalysed the WO of citric, lactic, malic and tartaric acids predominantly via a complexation-based reaction mechanism.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-147).
As production of shale gas has increased greatly in the United States, the amount of stranded shale gas that is flared as carbon dioxide has become significant enough to be considered an environmental hazard and a wasted resource. The conversion of methane, the primary component of natural gas, into methanol, an easily stored liquid, is of practical interest. However, shale wells are generally inaccessible to reforming facilities, and construction of on-site, conventional methanol synthesis plants is cost prohibitive. Capital costs could be reduced by the direct conversion of methane into methanol at low temperature. Existing strategies for the partial oxidation of methane require harsh solvents, need exotic oxidizing agents, or deactivate easily. Copper-exchanged zeolites have emerged as candidates for methanol production due to high methanol selectivity (> 99%), utilization of oxygen, and low reaction temperature (423-473 K). Despite these advantages, three significant shortcomings exist: 1) the location of surface intermediates on the zeolite is not well understood; 2) methane oxidation is stoichiometric, not catalytic; 3) there are few active sites and methanol yield is low. This work addresses all three shortcomings. First, a new reaction pathway is identified for methane oxidation in copper-exchanged mordenite zeolites using tandem methane oxidation and Koch carbonylation reactions. Methoxy species migrate away from the copper active sites and adsorb onto Bronsted acid sites, signifying spillover on the zeolite surface. Second, a process is developed as the first instance of the catalytic oxidation of methane into methanol at low temperature, in the vapor phase, and using oxygen as the oxidant. A variety of commercially available copper-exchanged zeolites are shown to exhibit stable methanol production with high methanol selectivity. Third, catalytic methanol production rates and methane conversion are further improved 100- fold through the synthetic control of copper speciation in chabazite zeolites. Isolated monocopper species, directed through the one-pot synthesis of copper-exchanged chabazite zeolites, correlates with methane oxidation activity and is likely the precursor to the catalytic site. Together, these synthetic methods provide guidelines for catalyst design and further improvements in catalytic activity.
by Karthik Narsimhan.
Ph. D.

This project is focused on the synthesis, modification and characterization of rhodium based catalysts supported on MCM-41 mesoporous silica to produce well-defined active sites for catalysis of CO oxidation at low-temperature. The Rh catalysts were prepared by incipient wetness impregnation (IWI) then modified by the inclusion of different transition metal oxides (ca. CeOx, ZrOx, CrOx, Ce0.5Zr0.5Ox and Ce0.5Cr0.5Ox) via two different routes. The first was achieved by pre-modification of MCM-41 support during its synthesis using the inorganic precursors of the promoter oxides followed by the addition of the specified Rh precursor (0.5 - 2.5 wt%), i.e. post-synthesis of Rh catalysts. The second route was performed by the post addition of the promoters using their non-inorganic sources [ca. Ce(acac)3, Zr(acac)4 and bis(benzene)chromium] by the controlled surface modification (CSM) method. The catalysts were characterized by using TGA, FT-IR, N2 physisorption analysis, PXD, SEM-EDX, TEM, DR UV/Vis spectroscopy and XPS. Furthermore, the structure-performance relationship and the dependence of the preparation method towards CO oxidation were also investigated by in situ QEXAFS-MS spectroscopy in the temperature range of 300 - 573 K. The combination of soft and hard X-ray absorption edges was applied to in situ structural studies. In addition to the Rh K-edge, the Ce L3, Zr K or Cr K-edges were used as probes of the catalysts as a function of temperature (300 - 573 K) under of different ambient gases (He, 10% H2/He, 10% O2/He and 10% CO/O2/He) during activation and reaction conditions. As a result, the fractions of Rh active species, coordination numbers and atom-to-atom distances were extracted from analysis of XANES and EXAFS results. In addition, the turnover frequency (TOF) values and CO conversion% over these catalysts were also calculated. The results revealed that Rh species and/or the promoter oxides prepared by both two methods were well confined into the mesoporous framework of silica support in amorphous nano-sized scale. However, the distribution of the Rh atoms and/or the promoter oxides depends mainly on the preparation method with much more homogeneity and local vicinity in those prepared by the CSM method. Furthermore, the preparation method played a crucial rule not only in the local structure, but also in the catalysts performance towards CO oxidation with high activity for catalysts prepared by CSM.

In this paper the composites Ag / SiO2 with regularly distributed in bulk matrix silver and copper oxide nanoparticles were synthesized. Herewith, copper ions was introduced into porous support at the stage of sol-gel synthesis. Sample Ag / CuO / SiO2 was tested by the catalytic reaction of CO oxidation and com-pared with Ag / SiO2. It was revealed that sample with introduced copper show lower activity .This fact can be explained by formation of silver cuprate during preparation of composite Ag / CuO / SiO2. Treatment by reaction mixture (CO and O2) led to release of silver in ionic, clusters and metal states that increased cata-lytic activity of the composite. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35611

Робота виконана на кафедрі хімічних технологій та водоочищення Черкаського державного технологічного університету Міністерства освіти і науки України.
Дисертація присвячена питанням розробки технологій інтенсифікації первинних ендотермічних стадій реакцій горіння та окиснення сировини, що містять вуглеводневі гази і тверді вуглеводні, які базуються на використанні направленої дії штучно створеної низькотемпературної плазми з упорядкованим рухом «повільних» електронів в присутності гетерогенного каталізатору та визначення оптимальних умов проведення цих процесів. Розроблений новий напрям в проведенні окиснювальних процесів, який базується на використанні для інтенсифікації первинних ендотермічних стадій реакцій горіння та окиснення сировини, що містить вуглеводневі гази і тверді вуглеводні, низькотемпературної плазми з упорядкованим рухом «повільних» електронів в присутності гетерогенного каталізатору. Штучно створена низькотемпературна нерівноважна плазма, при її короткотривалій дії на об’єкт горіння або окиснення, дає можливість проводити хімічні реакції, які в звичайних умовах можливі при значних енерговитратах або не протікають, або протікають дуже повільно. Мінімізація енерговитрат в процесах, що пропонуються, досягається з використанням каталізу в зоні розряду. Для створення низькотемпературної плазми запропоновано використання бар′єрного та об′ємного розрядів. Цей напрям отримав назву електронно-каталітичний метод. Використання цього методу в процесах горіння і окиснення дозволяє витрачати на процес інтенсифікації ендотермічних стадій значно меншу кількість енергії завдяки використанню енергії «повільних» електронна, на утворення яких впливає нерівноважна плазма. При горінні паливної суміші в предполумьяній зоні значно зменшується вміст води, на руйнування якої витрачалося велика кількість енергії. Замість неї утворюються радикали і іони, теплоємність яких значно менше теплоємності води і завжди має негативне значення. Енергія, яка витрачалася на руйнування, додається до сумарної енергії, що надають електрони і протони. Сумарний енергетичний внесок всіх утворюються при з'єднань, достатній, щоб ініціювати як процес горіння, так і окислення різних з'єднань. Для газової фази досягався додатковий енергетичний ефект в розмірі 12-15% від кількості енергії, що виділяється при звичайному згорянні палива.
Dissertation is devoted to the development of technologies for the intensification of endothermic stages of combustion and oxidation reactions on hydrocarbon gases and solid hydrocarbons based on the directional action of artificially created low-temperature plasmas with the ordered motion of "slow" electrons in the presence of a heterogeneous catalyst and determining the optimum conditions for carrying out these processes. A new direction has been developed in carrying out oxidation processes, which are based on the use of a low-temperature plasma with the ordered motion of "slow" electrons in the presence of a heterogeneous catalyst for the intensification of the endothermic stages of combustion and oxidation reactions on hydrocarbon gases and solid hydrocarbons. An artificially created low-temperature nonequilibrium plasma, with its short-term action on the object of combustion or oxidation, makes it possible to conduct a chemical reaction, which under normal conditions is possible at considerable energy costs, or proceed very slowly. Minimization of energy consumption in the proposed processes is achieved by using catalysis in the discharge zone. To create a low-temperature plasma, it is proposed to use a barrier and volume discharge. This direction was called the electron-catalytic method. The use of this method in combustion and oxidation processes allows a much smaller amount of energy to be expended on the process of intensification of endothermic stages due to the use of the energy of "slow" elecrons, the formation of which is affected by the nonequilibrium plasma. When the fuel mixture burns in the presumed zone, the water content significantly decreases, and a large amount of energy is consumed to destroy it. Instead, radicals and ions are formed, the heat capacity of which is much less than the heat capacity of water and always has a negative value. Energy, which was spent for destruction, is applied to the total energy that exerts electrons and protons. The total energy contribution of all compounds formed during the compounds is sufficient to initiate both the burning process and the oxidation of various compounds. For the gas phase, an additional energy effect was achieved in the amount of 12-15% of the amount of energy released during the usual combustion of fuel.
Диссертация посвящена вопросам разработки технологий интенсификация эндотермических стадий реакций горения і окисления углеводородные газы и твердые углеводороды, которые базируются на использовании направленного действия искусственно созданной низкотемпературной плазм с упорядоченным движением «медленных» электронов в присутствии гетерогенного катализатора и определении оптимальных условий проведения этих процессов. Разработано новое направление в проведении окислительных процессов, которые базируются на использовании низкотемпературной плазмы с упорядоченным движением «медленных» электронов в присутствии гетерогенного катализатора для интенсификация эндотермических стадий реакций горения і окисления на катализаторах углеводородные газы и твердые углеводороды,. Искусственно созданная низкотемпературная неравновесная плазма, при её кратковременном действии на объект горения или окисления, дает возможность проводить химическую реакцию, которые в обычных условиях возможны при значительных энергозатратах, или протекают очень медленно. Минимизация энергозатрат в предлагаемых процессах достигаются при использовании катализе в зоне разряда. Для создания низкотемпературной плазмы предложено использовать барьерный и объемный разряд. Это направление получило название электронно-каталитический метод (ЭКМ). Использования этого метода в процессах горения и окисления позволяет расходовать на процесс интенсификации эндотермических стадий значительно меньшее количество энергии благодаря использованию энергии «медленных» элекронов, на образование которых влияет неравновесная плазма. При горении топливной смеси в предполумьяний зоне значительно уменьшается содержание воды, на разрушение которой расходовалось большое количество энергии. Вместо нее образуются радикалы и ионы, теплоемкость которых значительно меньше теплоемкости воды и всегда имеет отрицательное значение. Энергия, которая тратилась на разрушение, прилагается к суммарной энергии, оказывающих электроны и протоны. Суммарный энергетический вклад всех образующихся при соединений, достаточный, чтобы инициировать как процесс горения, так и окисления различных соединений. Для газовой фазы достигался дополнительный энергетический эффект в размере 12-15% от количества энергии, выделяемую при обычном сгорании топлива. В условиях ЭКМ на химический процесс влияют факторы: упругое и неупругое соприкосновения электронов и частиц, Ионизация, колебательное возбуждение и диссоциация молекул, температурная неоднородность между газовым потоком и потоком низкотемпературной плазмы, резонанс частоты колебаний молекул и электрического разряда. Существенное влияние оказывают диссоциативное прилипания, которое протекает при соприкосновении электронный с молекулой с образованием промежуточного агента - отрицательно заряженного иона, который затем разлагается на фрагменты, один из которых имеет отрицательный заряд и электронное возбуждение. При использовании низкотемпературной плазмы перед зоной реакции возникают резонансные частоты колебаний, которые могут вступать в резонанс с молекулой и инициировать первичные стадии горения и окисления сырья. Для электрического барьерного разряда характерно ряд температурных неоднородностей. При наложении электрического разряда на пламя под действием электромагнитного поля и потока электронов происходит направленное движение положительных частиц, которые образуются в пламени. Под действием электронов количество этих ионов увеличивается. Действие этого направленного движения ионизированных частиц увеличивает скорость процесса горения, благодаря более интенсивному движению частиц и изменении поверхности контакта. Использование ЭКМ интенсификации процесса горения твердого топлива позволяет повысить выход летучих соединений, в составе которых содержатся вещества, теплоты сгорания которых значительно выше, чем теплота сгорания веществ, которые образовались при обычном термолизе. Кроме того, использование ЭКМ приводит к образованию летучих соединений при значительно меньших температурах, что позволяет использовать избыток теплоты, образовавшийся на целевые нужды. Были проведены исследования горения и окисления углеводородных газов, в результате которых установлено: - оптимальные условия проведения электронно-каталитической интенсификации первичных стадий процессов горения и окисления газообразного и твердого топлива. Достигнуты значительные повышения выделения тепла для различных видов топлива. - влияние состава катализаторов на процесс окисления и горения газообразного топлива. Для ЭКМ наиболее эффективны катализаторы, содержащие никель и хром. - влияние параметров напряжения и формы синусоиды тока на процесс горения газообразного топлива. Наибольший эффект достигается при увеличении напряжения разряда и нижней синусоиде тока. Исследован процесс неполного окисления метана с использованием ЭКМ с образованием формальдегида и метанола. Получены зависимости формальдегида при разных составах исходной смеси и температуре. Для процесса сжигания твердого топлива определено влияние напряжения на процесс выделения газообразных веществ при термолизии топлива. Полученные зависимости выделение тепла от напряжения при сжигании антрацита, древесины и пеллет. При использовании ЭКМ в процессах горения достигнуто уменьшение выбросов оксидов углерода (II) до 52% и оксидов азота до 80% при сжигании твердого топлива. Составлены и решены математические модели процессов горения углеводородных газов, угля и древесины, процесса неполного окисления метана и формальдегид. Были предложены методы электронно-каталитической интенсификации процесса горения газообразного топлива, угля и древесины; метод синтеза формальдегида при атмосферном давлении.

Alumina supported manganese oxides were used in the gas phase oxidation of toluene by ozone. Catalyst activity and characterization, the promotional effect of noble metals (Pt and Pd) on the activity of manganese oxides, and the kinetics and mechanism of the reaction were investigated in this PhD thesis. It was shown that MnO2 and Mn2O3 were the active sites of the catalyst capable of oxidizing toluene to CO and CO2 below 100 oC. Catalysts were deactivated at room temperature due to the accumulation of carbonaceous species on their surface. At least 65 oC was required for the stable operation of the catalysts. X-ray absorption spectroscopy was used to study the structure and electronic properties of the mono metallic and bimetallic catalysts. It was found that the catalysts with higher Mn loading resulted in higher oxidation states of Mn which were less favorable for the oxidation of toluene. The addition of Pt to the Mn containing catalyst increased the reaction rate by transferring electrons from Pt to Mn. On the other hand, no promotional effect was observed by the addition of Pd to Mn. The Oxidation state of Mn atoms was one of the most important parameters, controlling the rate of toluene oxidation. Lower oxidation states of Mn were able to easily transfer electrons to ozone, accelerating the rate of toluene oxidation. A reaction mechanism was proposed for the catalytic oxidation of toluene over manganese oxides. In this mechanism, the oxidation of toluene was carried out by the abstraction of hydrogen atoms followed by the oxidation of toluene carbon skeleton. A rate equation was derived based on this mechanism, determining the reaction orders of -1 and 2 for toluene and ozone, respectively. It was concluded that catalytic ozonation is an effective method for the low temperature oxidation of volatile organic compounds (VOCs) in air. The significance of this method is related to energy saving in air purifying systems by reducing the required temperature to oxidize VOCs. Catalytic ozonation can be used in indoor and outdoor applications for removal of VOCs from enclosed environments or polluted industrial streams.

碩士
國立中正大學
化學工程研究所
88
Abstract Hydrophobic catalysts, Pt/SDB (Styrene Divinylbenzene Copolymer), patented by Dr. Chuang (Alberta University, Canada) have been used for the destruction of volatile organic compounds (VOC) in wastewater. The test reactions indicated that the catalysts present excellent performance at low concentration but poor in high VOC concentration. Because of the heat removal problem, oxidative reaction would be happen within the catalyst leading to rapid aging and crumbling. For the petrochemical industry in Taiwan, the rather high VOC containing in wastewater (usually higher than 10,000 ppm) limit the application of Pd/SDB catalysts. Since Pt/Zeolite of high silica to alumina ratio also has the hydrophobic characteristic and endures much higher temperature than Pd/SDB do, they are chosen for the treatment of wastewater containing high VOC. As expected, the catalysts present not only high conversion but also good stability maintenance. Because of their high stability and regenerability, the catalysts were regarded to be promising for industrial application and the feed reactivity then was tested. The experimental results indicated that the reaction rate is inversely proportional to the molecular weight for the compounds with same functional group and aldehyde is easier to be destructed than alcohol. To minimize the energy consumption, liquid phase reaction was preferred since the heat of reaction could maintain the reaction temperature.

Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10–15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. There are many factors that influence the outcome of enzymatic reactions in carbon dioxide. These include enzyme activity, enzyme stability, temperature, pH, pressure, diffusional limitations of a two-phase heterogeneous mixture, solubility of enzyme and/or substrates, water content of the reaction system, and flow rate of carbon dioxide (continuous and semibatch reactions). It is important to understand the aspects that control and limit biocatalysis in carbon dioxide if one wants to improve upon the process. This chapter serves as a brief introduction to enzyme chemistry in carbon dioxide. The advantages and disadvantages of running reactions in this medium, as well as the factors that influence reactions, are all presented. Many of the reactions studied in this area are summarized in a manner that is easy to read and referenced in Table 6.1. Carbon dioxide is cited as a good choice of solvents for a number of reasons. Some of the advantages of running reactions in carbon dioxide instead of the more traditional organic solvents include the low viscosity of the solvent, the convenient recovery of the products and non-reacted components, abundant availability, low cost, no solvent contamination of products, full miscibility with other gases, non-existent toxicity, low surface tension, non-flammability, and recyclability. The low mass-transfer limitations are an advantage because of the large diffusivity of reactants.

As described in other chapters of this book and elsewhere (Jessop, 1999), a wide range of catalytic reactions can be carried out in supercritical fluids, such as Fischer–Tropsch synthesis, isomerization, hydroformylation, CO2 hydrogenation, synthesis of fine chemicals, hydrogenation of fats and oils, biocatalysis, and polymerization. In this chapter, we describe experiments aimed at addressing the potential of using supercritical carbon dioxide (and carbon dioxide/propane mixtures) for applications in the hydrogenation of vegetable oils and free fatty acids. Supercritical fluids, particularly carbon dioxide, offer a number of potential advantages for chemical processing including (1) continuously tunable density, (2) high solubilities for many solids and liquids, (3) complete miscibility with gases (e.g., hydrogen, oxygen), (4) excellent heat and mass transfer, and (5) the ease of separation of product and solvent. The low viscosity and excellent thermal and mass transport properties of supercritical fluids are particularly attractive for continuous catalytic reactions (Harrod and Moller, 1996; Hutchenson and Foster, 1995; Kiran and Levelt Sengers, 1994; Perrut and Brunner, 1994; Tacke et al., 1998). There are a number of reports on hydrogenation reactions in supercritical fluids using homogenous and heterogeneous catalysts (Baiker, 1999; Harrod and Moller, 1996; Hitzler and Poliakoff, 1997; Hitzler et al., 1998; Jessop et al., 1999; Meehan et al., 2000; van den Hark et al., 1999). We have investigated the selective hydrogenation of vegetable oils and the complete hydrogenation of free fatty acids for oleochemical applications, since there are some disadvantages associated with the current industrial process and the currently used supported nickel catalyst. The hydrogenation of fats and oils is a very old technology (Veldsink et al., 1997). It was invented in 1901, by Normann, in order to increase the melting point and the oxidation stability of fats and oils through selective hydrogenation. Since the melting point increases during the hydrogenation, the reaction is also referred to as hardening. The melting behavior of the hydrogenated product is determined by the reaction conditions (temperature, hydrogen pressure, agitation, hydrogen uptake). Vegetable oils (edible oils) are hydrogenated selectively for application in the food industry; whereas free fatty acids are completely hydrogenated for oleochemical applications (e.g., detergents).

A novel, low temperature Organometallic Chemical Vapour process (LOM), developed by Liburdi Engineering is presented in this paper. The process, which is widely used in the electronics industry to apply thin layers of pure aluminum, has been successfully scaled from a 3″ (75 mm) diameter quartz reactor to a production hot wall metal retort with an internal diameter of 18″ (0.45m) and a height of 60″ (1.5m). The capability for simultaneously coating external and internal surfaces is discussed. The aluminum layer can be used directly for low temperature atmospheric corrosion protection in place of IVADIZING or diffusion heat treated to produce an oxidation resistant aluminide coating for superalloys. Results of cyclic oxidation and salt fog corrosion testing are presented. The potential for alloying with modifying elements such as platinum to further enhance its high temperature oxidation resistance and to use the process in conjunction with thermal barrier coatings are presented. Potential applications ranging from coating of heat exchangers and automotive catalytic converters to the coating of industrial and aero turbine blades with complex cooling passages are presented.

Exhaust gas recirculation (EGR) treatment techniques that include combustible substance oxidation, catalytic fuel reforming, and partial bypass-flow control have been experimentally investigated on a single cylinder diesel engine. Application tests are conducted to investigate the effects of the reformed gases on the diesel combustion characteristics and exhaust emissions. This research is aimed at stabilizing and expanding the limits of heavy EGR during steady and transient operations by enhancing the premixed combustion that may significantly alleviate problems with soot formation and cyclic variations. Additionally, the heavy treated EGR is applied to enable in-cylinder low temperature combustion. A preliminary investigation on the effects of water addition to the high temperature catalyst bed is also conducted. The potential of EGR reforming is also examined for possible generation of synthetic EGR (CO2) at low engine loads. The effectiveness of the treated EGR on engine emission and operating characteristics are therefore reported.

Micro-solid oxide fuel cell (SOFC) power plants are emerging as a promising alternative for power generation for portable applications due to their low emission of pollutants, high power density and fuel flexibility. Some of the challenges for developing such micro-SOFC power plants are geometrical compactness, fast start-up and self-sustainability at operating conditions. In this work, we present a hybrid start-up process for a micro-SOFC power plant using catalytic oxidation of n-butane over Rh-doped Ce0.5Zr0.5O2 nanoparticles in a small-scale reactor to provide the necessary intermediate operating temperature (500–550 °C) and syngas (CO + H2) as fuel for a micro-SOFC membrane. A short heating wire is used to generate the heat required to trigger the oxidative reaction. The hybrid start-up is investigated for partial oxidation (POX) and total oxidation (TOX) ratios at one specified flow rate. Additionally, the variation of electrical heating time and its influence on the hybrid start-up is evaluated.

Results are presented of an experimental laboratory investigation of the oxidation reactions of heated low velocity streams of homogeneous lean fuel-air mixtures within a packed bed tubular reactor at atmospheric pressure in the presence of non-noble metal oxides catalysts. The main fuel considered was methane, however, other common gaseous fuels, i.e. propane, carbon monoxide, hydrogen and ethylene were also examined for comparative purposes. It was shown that binary cobalt oxide/chromium oxide catalysts can be effective in the oxidation of very lean fuel-air mixtures. Furthermore, there is an optimum value of their mass ratio that could produce a significant improvement to the low temperature oxidation of the lean mixtures examined and the corresponding resulting emissions.

The objective of this paper is modeling the mechanism of high temperature catalytic oxidation of natural gas, or methane. The model is two-dimensional steady-state, and includes axial and radial convection and diffusion of mass, momentum and energy, as well as homogeneous (gas phase) and heterogeneous (gas-surface) single step irreversible chemical reactions within a catalyst channel. Experimental investigations were also made of natural gas, or methane combustion in the presence of Mn-substituted hexaaluminate catalysts. Axial profiles of catalyst wall temperature, and gas temperature and gas composition for a range of gas turbine combustor operating conditions have been obtained for comparison with and development of a computer model of catalytic combustion. Numerical calculation results for low pressure agree well with experimental data. The calculations have been extended for high pressure (10 atms) operating conditions of gas turbine.

The performance of Cu-Ce-Al-oxide and Cu-Cr-Al-oxide catalysts of varying compositions prepared by co-precipitation method was evaluated for the PEM fuel cell grade hydrogen production via oxidative steam reforming of methanol (OSRM). The limitations of partial oxidation and steam reforming of methanol for the hydrogen production for PEM fuel cell could be overcome using OSRM and can be performed auto-thermally with idealized reaction stoichiomatry. Catalysts surface area and pore volume were determined using N2 adsorption-desorption method. The final elemental compositions were determined using atomic absorption spectroscopy. Crystalline phases of catalyst samples were determined by X-ray diffraction (XRD) technique. Temperature programmed reduction (TPR) demonstrated that the incorporation of Ce improved the copper reducibility significantly compared to Cr promoter. The OSRM was carried out in a fixed bed catalytic reactor. Reaction temperature, contact-time (W/F) and oxygen to methanol (O/M) molar ratio varied from 200–300°C, 3–21 kgcat s mol−1 and 0–0.5 respectively. The steam to methanol (S/M) molar ratio = 1.4 and pressure = 1 atm were kept constant. Catalyst Cu-Ce-Al:30-10-60 exhibited 100% methanol conversion and 152 mmol s−1 kgcat−1 hydrogen production rate at 300°C with carbon monoxide formation as low as 1300 ppm, which reduces the load on preferential oxidation of CO to CO2 (PROX) significantly before feeding the hydrogen rich stream to the PEM fuel cell as a feed. The higher catalytic performance of Ce containing catalysts was attributed to the improved Cu reducibility, higher surface area, and better copper dispersion. Reaction parameters were optimized in order to maximize the hydrogen production and to keep the CO formation as low as possible. The time-on-stream stability test showed that the Cu-Ce-Al-oxide catalysts subjected to a moderate deactivation compared to Cu-Cr-Al-oxide catalysts. The amount of carbon deposited onto the catalysts was determined using TG/DTA thermogravimetric analyzer. C1s spectra were obtained by surface analysis of post reaction catalysts using X-ray photoelectron spectroscopy (XPS) to investigate the nature of coke deposited.

Platinum based catalysts are well known as the most active ones among noble metals for oxidation of hydrocarbons as well as hydrogen. Microcombustion experiments using bare Pt foil catalyst have shown that hydrocarbon fuels (e.g. propane) can be oxidized at low-temperature (< 60 °C) and ignited (< 90 °C) by treating the catalyst surface by burning propane-air mixtures with ∼ 5% of the propane replaced by ammonia for half an hour. This NH3 pre-treatment etches the catalyst surface and creates surface structures on the scale of few μms, completely unlike those without NH3 treatment. This change in structure with NH3 treatment is noteworthy in that it increases the performance of the catalyst by a factor of 3, but only for low Re, corresponding to conditions with low maximum reaction temperatures characteristic of microcombustors. However, no similar such low-temperatures were found without NH3 pre-treatment, even for catalytic reactions. This is not merely a surface area effect, since increasing bulk catalyst area had almost no effect on combustion performance. Nevertheless, it may be possible to further extend reaction and ignition to even lower temperatures by examining alternative hydrocarbon fuels and catalysts. Self-starting fuels and catalysts are highly desirable, especially for the micro-combustors used for MEMS (Micro Electro-Mechanical Systems) power generators, because it would eliminate the need for glow plugs, supplemental battery, electronics, etc. associated with active ignition systems.

Urea-selective catalytic reduction (SCR) catalysts are regarded as the leading NOx aftertreatment technology to meet the 2010 NOx emission standards for on-highway vehicles running on heavy-duty diesel engines. However, issues such as low NOx conversion at low temperature conditions still exist due to various factors, including incomplete urea thermolysis, inhibition of SCR reactions by hydrocarbons and H2O. We have observed a noticeable reduction in the standard SCR reaction efficiency at low temperature with increasing water content. We observed a similar effect when hydrocarbons are present in the stream. This effect is absent under fast SCR conditions where NO ∼ NO2 in the feed gas. As a first step in understanding the effects of such inhibition on SCR reaction steps, kinetic models that predict the inhibition behavior of H2O and hydrocarbons on NO oxidation are presented in the paper. A one-dimensional SCR model was developed based on conservation of species equations and was coded as a C-language S-function and implemented in Matlab/Simulink environment. NO oxidation and NO2 dissociation kinetics were defined as a function of the respective adsorbate’s storage in the SCR catalyst. The corresponding kinetic models were then validated on temperature ramp tests that showed good match with the test data.