No description available.

No description available.

Deactivation of titania-supported vanadia commercial SCR catalysts exposed to flue gases from both coal and coal-biomass co-firing boilers were investigated. BET surface area and average pore diameter measurements on both fresh and exposed commercial catalyst samples indicated pore plugging occurred to exposed catalyst samples. ESEM analyses showed fouling on catalyst surface, and poison deposition on both catalyst surface and inner pores. Activity assessments of commercial monolith catalysts with various exposures (time and fuel type) indicated that catalyst deactivation involves fouling, pore plugging, and poisoning. Different mechanisms may dominate depending on exposure time, catalyst properties, and combustion environment. Better controlled lab-scale investigations involved poisoning and sulfation of SCR vanadia/titania catalysts synthesized with an incipient impregnation method. In situ FTIR spectroscopy indicate that K, Na, and Ca (among others materials) reduce, and sulfation and tungsten increase ammonia adsorption intensity on Brønsted acid sites. Activity measurements by MS showed K, Na, and Ca poison SCR catalysts, and sulfation and tungsten enhance SCR NOx reduction activity. Both the decrease and increase of catalyst activity arise from the decrease and increase of the pre-exponential factor (A) correspondingly. Moreover, the decrease of NO reduction activity from each poison are consistent with the IR peak area decrease of ammonia adsorbed on Brønsted acid site caused by the corresponding poison but not Lewis acid sites. Therefore, Brønsted acid sites participate more actively in SCR reaction than Lewis acid sites. However, Brønsted acid sites itself do not possess NOx reduction activity as indicated by zero NO conversion on 9% W/Ti which shows large amounts of Brønsted acid sites population. Therefore, dual acid (Brønsted) -redox (vanadia) sites are suggested to provide the active center during catalytic reduction cycle with weakly adsorbed or gas phase NOx reacts with surface adsorbed ammonia. In addition, in situ FTIR spectroscopy combined with XPS analyses indicate that sulfate does not form on vanadia sites but on titania sites.

No description available.

No description available.

In der vorliegenden Arbeit wurden Cluster- und QM/MM-Einbettungsmodelle für geträgerte Vanadiumoxidkatalysatoren auf Siliziumdioxid mit Hilfe von DFT-Rechnungen untersucht. Es wurden Strukturen, Schwingungen und die Stabilität gegenüber Wasser und Sauerstoff unter Reaktionsbedingungen betrachtet. Ferner wurde die Reaktivität bei der Oxidativen Dehydrierung (ODH) von n-Propan zu n-Propen und der Oxidation von Methanol zu Formaldehyd untersucht. Zur Durchführung der Einbettungsrechnung wurde ein angepasstes Shell-Model-Potential verwendet. Bezüglich der Schwingungen zeigte sich, dass sich der Einfluss der Einbettung hauptsächlich auf die Kopplung von Schwingungen beschränkt, aber die Frequenzen kaum verändert werden. Die lokale Struktur um das Vanadiumatom beeinflusst die Vanadylschwingung wenig. Die Stabilitätsberechnungen haben gezeigt, dass die untersuchten Modelle unter Reaktionsbedingungen vorliegen und hydroxylierte Spezies keine Bedeutung haben. Bei der Untersuchung der beiden Reaktionen wird für die Cluster- und die QM/MM-Einbettungsrechnungen jeweils derselbe Mechanismus gefunden. Der Vorteil der Einbettungsrechnungen besteht darin, dass die lokale Struktur um das aktive Zentrum variiert werden kann. Bei der ODH von Propan hat die lokale Struktur einen eher geringen Einfluss auf die Reaktionsenergien, denn die Reaktion verläuft hauptsächlich am Vanadylsauerstoff. Der Übergangszustand des geschwindigkeitsbestimmenden Schrittes liegt bei der Einbettungsrechnung dennoch energetisch höher. Grund ist eine sterische Hinderung durch die Hydroxylgruppen der Oberfläche. Bei der Oxidation von Methanol ist der Einfluss der lokalen Struktur größer, denn die Reaktion verläuft sowohl über den Vanadylsauerstoff als auch über die Brückensauerstoffatome zum Trägermaterial. Für beide Reaktionen wird ein Einfluss der Vanadiumbeladung auf die Reaktionsenergien gefunden. Bei höherer Beladung werden die Reaktionen exothermer. / In this work cluster models and models for QM/MM-embedding for supported vanadia catalysts on silica were studied with help of DFT-calculations. The structures, vibrations and stability towards water and oxygen under reaction conditions were examined. Furthermore the reactivities towards the oxidative dehydrogenation (ODH) of n-propane to n-propene and the oxidation of methanol to formaldehyde were tested. For the embedding an adapted shell-model-potential was employed. Regarding the vibrations it was shown that the influence of the embedding lies mostly in the coupling of vibrations and not in their frequencies. The local structure surrounding the vanadium atom has only minor influence. The stability calculations have shown that the tested model systems exist under reaction conditions while hydroxylated species do not exist. When studying the reactivity of the two reactions always the same mechanism is found for cluster and embedded calculations. The benefit of the embedded calculations is the possibility to vary the local structure surrounding the active center. For the ODH of propane the local structure has only small impact on reaction energies because the reaction takes mainly place at the vanadyl oxygen. The transition state of the rate determining step nevertheless is energetically higher in the embedded calculations due to steric hindrance caused by the hydroxyl groups of the surface. The impact of local structure is more important for the oxidation of methanol since in this case vanadyl oxygen and bridging oxygens to the support are involved in the reaction. For both reactions an influence on reaction energies of the vanadia loading is found. With more loading the reactions becomes more exothermic.

Unter Verwendung von Dichtefunktionaltheorie werden die katalytischen Eigenschaften von Cerdioxidoberflächen mit verschiedenen Terminierungen untersucht. Cerdioxid wird auch als Trägermaterial in der heterogenen Katalyse eingesetzt, um Aktivität, Selektivität und Stabilität der aktiven Komponente zu erhöhen. In dieser Arbeit werden geträgerte Vanadiumoxidcluster diskutiert. Dabei wird die oxidative Dehydrierung von Methanol als Modellreaktion zur Aktivierung von C-H-Bindungen genutzt. Ceroxidpartikel werden oft in wässriger Lösung synthetisiert. Damit hängt die Form der Nanokristallite direkt von der relativen Stabilität der unterschiedlichen Terminierungen in der Gegenwart von Wasser ab. Außerdem ist Wasser an zahlreichen Reaktionen entweder als Produkt, Edukt oder Lösungsmittel beteiligt. Aus diesem Grund werden auch die Wasser-Oberflächenwechselwirkungen untersucht. Des Weiteren wird die Genauigkeit von drei verschiedenen Funktionalen (B3LYP, HSE und PBE+U) durch den Vergleich mit experimentellen Daten evaluiert. Diese beinhalten Barrieren, die mittels Temperatur-programmierter Desorptionsspektroskopie erhalten wurden, und Schwingungsspektren. / Density functional theory is applied to study the catalytic properties of ceria surfaces with different terminations. Ceria is also used as a support material in heterogeneous catalysis to improve activity, selectivity, and stability of the active component. In this work, supported vanadia clusters are discussed. The oxidative dehydrogenation of methanol is used as a model reaction for C–H bond activation. Ceria catalysts are often prepared in aqueous solution. As a result, the shape of ceria nanocrystallites depends on the relative stability of the different surface terminations in the presence of water. Furthermore, many reactions involve water either as a product, as a reagent, or as a solvent. Hence, water–surface interactions are studied as well. Furthermore, the accuracy of three different functionals (B3LYP, HSE, and PBE+U) is assessed by comparison to experimental data such as barriers obtained via temperature-programmed desorption and infrared spectra.

Bio-inspired or biomimetic chemistry deals with the replication of the nature’s fundamental processes, which can help in understanding the functioning of biological systems and develop novel applications. Although a large number of researchers worked towards the replication of natural synthetic pathways through biogenetic syntheses, enzyme mimicry by the small organic molecules and inorganic complexes emerged in leaps and bounds over the years. The development of biomimetic chemistry then continued in designing the molecules that can function like enzymes. And now, with the advent of nanotechnology, nanostructured materials have been shown to exhibit enzyme-like activities (nanozymes). Interestingly, the two distinct fields, biology and materials science, have been integrated to form an entirely new area of research that has captured a great attention. Along with the pronounced application of nanomaterials as drug delivery vehicles, anticancer agents, antimicrobials, etc., research is also focused on designing nanomaterials for the biomimetic applications. The thesis consists of five chapters. The first chapter provides a general overview of the recently discovered nanozymes that mimic heme-peroxidase, oxidase, superoxide dismutase, catalase, haloperoxidase and phosphatase. This chapter also deals with the nanozymes’ application in sensing and immunoassay, and as antioxidants, neuroprotective agents. The factors affecting the nanozymes’ activity and the challenges associated with them is also covered in this chapter. Chapter 2 is divided into two parts and it deals with the biomimetic properties of graphene-based materials. In part A, the remarkable peroxynitrite (PN) reductase and isomerase activities of hemin-functionalized reduced graphene oxide (rGO) is discussed. In part B, the activity of graphene oxide (GO) as peroxide substrate for the glutathione peroxidase (GPx) enzyme is discussed. In chapter 3, the oxidant material, V2O5, is shown to exhibit significant GPx-like antioxidant activity in its nano-form. Chapter 4 deals with the oxidase-like activity of MnFe2O4 nanooctahedrons for the antibody-free detection of major oxidative stress biomarker, carbonylated proteins. In chapter 5, the phosphotriesterase mimetic role of vacancy engineered nanoceria is discussed. instead of H2O2 for glutathione peroxidase (GPx) enzyme. As partial reduction of GO was observed when treated with GPx enzyme due to the fact that large sheet-like structures cannot be accessible to the active site, we studied the reaction with some GPx mimetics (Fig. 2). Varying the concentration of cofactor glutathione (GSH) required for the reaction, GPx mimic, ditelluride, could accomplish the reduction of GO following Michaelis-Menten kinetics. As the structure of GO is elusive and under active investigation, our study highlights the presence of peroxide linkages as integral part of GO other than hydroxyl, epoxy and carboxylic groups. This study also highlights an important fact that the modification of GO by biologically relevant compounds such as redox proteins must be taken into account when using GO for biomedical applications because such modifications can alter the fundamental properties of GO. Figure 2. The GO reductase and decarboxylase activities of GPx mimetic ditelluride compound, suggesting the presence of peroxide linkages on GO. In chapter 3, we have discussed about the novel antioxidant nanozyme that combats oxidative stress. During our attempts in the investigation of antioxidant nanozymes, we surprisingly noticed that the oxidant material, V2O5, shows significant GPx-like antioxidant activity in its nano-form. The Vn readily internalize in the cells and exhibit remarkable protective effects when challenged against reactive oxygen species (ROS). Although Vn has been shown to protect cells from ROS-induced damage, cells treated with bulk V2O5 and few vanadium complexes resulted in generation of ROS and severe toxicity. Detailed investigation on the mechanism of this interesting phenomenon Chapter 4 deals with the development of novel methodology for detection of biomarkers. Inspired by the use of antibodies and enzymes for detection of a specific antigen, we have shown for the first time that the nanozymes can entirely replace antibodies and enzymes in Enzyme-linked Immunosorbent Assays (ELISA). As a specific example, we focused on the antibody-free detection of chief oxidative stress biomarker, carbonylated proteins, as our target. To achieve this, we designed MnFe2O4 nanooctahedrons that can function as oxidase enzyme and form signaling point of detection. We functionalized MnFe2O4 nanooctahedrons with hydrazide terminating groups so that carbonylated proteins can be linked to nanozymes by hydrazone linkage (Fig. 4a). Treatment of various carbonylated proteins (hemoglobin (Hb), Myoglobin (Mb), Cytochrome c (Cyt c), RNase and BSA) coated in well plate with hydrazide-terminated MnFe2O4 nanooctahedrons and then with 3,3’,5,5’-tetramethylbenzidine substrate, resulted in instantaneous detection by well plate reader (Fig. 4b). Considering the challenges and difficulties associated with the conventional methods used to detect such modified proteins, this methodology opens up a new avenue for the simple, cost-effective, instantaneous and entirely antibody-free ELISA-type detection of carbonylated proteins. Our results provide a cumulative application of nanozymes’ technology in oxidative stress associated areas and pave a new way for direct early detection of post translational modification (PTM) related diseases. Figure 4. a) Nanozyme linked to the carbonylated protein coated on a plate through hydrazone linkage. b) General bar diagram showing detection of oxidized (carbonylated) proteins by nanozymes. Synopsis Figure 5. a) A cartoon view of surface of ceria showing vacancy. b) Zoomed portion of high resolution transmission electron microscopic image showing few vacancies on the surface of nanoceria. c) Catalytic mechanism of detoxification of paraoxon at the defect site. In the final chapter, chapter 5, we have discussed about the nanomaterial that can function as phosphotriesterase enzyme. Phosphotriesterase enzyme is a bacterial enzyme that is involved in the rapid hydrolysis of sarin gas-related deadly nerve agents such as paraoxon, parathion and malathion. When encountered with these orgnaophospatetriesters, living beings tend to undergo nerve shock to cause paralysis by inhibiting an extremely important enzyme called acetylcholine esterase. They are also known to cause severe oxidative stress problems and are associated with neurodegenerative disorders. Therefore, curbing the toxic effects and detoxification of these nerve agents is a world-wide concern and many research teams have focused their attention to address this important problem. Working on the development of nanozymes for important problems, we found that nanoceria, especially the vacancy engineered one (Fig. 5a,b), can serve as active mimic of phosphotriesterase enzyme in the presence of N-methylmorpholine (acting as a distal base histidine). Vacancy engineered nanoceria has been shown to catalyze the hydrolysis of high amounts of paraoxon quiet efficiently and within few minutes with very low activation energy and high kcat. Detailed mechanistic investigation revealed that the presence of both Ce(III) and Ce(IV) is very essential for detoxification activity (Fig. 5b). The vacancies on the surface of nanoceria, were the buried Ce(III) ions are directly exposed to the reaction environment, behave as hotspots or enzyme active sites for detoxification reaction (Fig. 5b).

Philosophiae Doctor - PhD / Energy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading-edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT). / 2023-12-01