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Methane is the primary component of natural gas, coal bed gases, shale gas and natural gas hydrates, and its commercially recoverable amounts exceed those of petroleum and coal by a few orders of magnitude. The strong C-H bonds of methane make its selective and controlled activation/dissociation difficult and this impedes the widespread utilization of this small alkane as a chemical feedstock to make value added chemicals, fuels and materials. Thus, developing alternate techniques, synthesising new catalytic materials and gaining fundamental mechanistic insights into C-H bond activation on known catalytic surfaces are pivotal to making ‘methane to chemicals and fuels’ a reality. Using state of the art quantum chemical simulations, it is shown for the first time that mechanical impact of methane molecules induces the dissociation of their strong C-H bonds. This novel bimolecular ‘coupling induced dissociation mechanism’ is demonstrated to convert methane molecules undergoing mechanical impact, directly to C2 hydrocarbons like ethane and ethylene. The impact induced vibrational excitation of the molecules allow successive transitions to lower potential energy states, leading to the concerted dissociation of C-H bonds of the molecules and coupling of the carbon atoms. Using ab initio molecular dynamics and Metadynamics simulations, it is shown that the mechanical impact of methane on an inactive transition metal like copper, in the form of nanoclusters, can dissociate it with activation free energy barriers between 60 and 90 kJ mol-1. The impact induced vibrational excitation of the molecule and the formation of a collision complex, which serves as a precursor for the dissociation of methane are key reasons for the low free energy barriers. Additionally, the small 3-dimensional copper nanoclusters have electronic structure and morphological features which favour the impact induced dissociation of methane while subsequent dehydrogenation steps have high barriers. The stabilization of the transition state and the products of dissociation (CH3 and H) by the under-coordinated Cu-O pair on the CuO surfaces, enable the dissociation of methane with an activation energy barrier as low as 76 kJ mol-1 on the most stable CuO(111) surface, compared to the barrier of 170 kJ mol-1 on Cu(111) surface. Thus, oxygen enhances the activity of copper in methane dissociation. The stronger the H chemisorption on the surface lattice oxygen on the different CuO surfaces, the more active is the surface in dissociating methane, making H chemisorption energy a descriptor for the reactivity of the surface. The weaker the copper- lattice oxygen interaction on the surface, the stronger is the H chemisorption on the lattice oxygen. The difference in the intrinsic metal- oxygen interaction on the different CuO surfaces is the root cause for the differences in their reactivity. In contrast to CuO, the 5-coordinated surface lattice oxygen on the most stable NiO surface, NiO(100), makes the surface inactive for methane dissociation with activation barrier of 136 kJ mol-1 compared to 70 kJ mol-1 on Ni(100) surface. NiO surfaces are as active as metallic Ni for methane dissociation when 1) the surface lattice oxygen is 4 coordinated as in the less stable NiO(110) surface; 2) NiO has surface Ni vacancies; and 3) NiO is doped with low valent dopants like Li. On comparing un-doped and doped surfaces, the H chemisorption energy, the descriptor for the reactivity of the lattice oxygen on different NiO surfaces, was found to have a weaker correlation with the intrinsic binding strength of the lattice oxygen on the surfaces. Low valent dopants like Li increase the activity of surface lattice oxygen for methane dissociation by lowering the binding strength of the surface lattice oxygen. In summary, this thesis reveals unusually high reactivity of methane resulting from collisional impact. The findings have implications for understanding of certain planetary phenomena, offer an explanation for the genesis of ‘abiogenic petroleum’ on the earth and also indicate opportunities for the commercial exploitation of methane. Insights into the role of lattice oxygen, vacancies and dopants on metal oxides in methane dissociation, and H chemisorption energy as a descriptor for reactivity can serve as guidelines in screening and designing efficient multifunctional catalysts for methane dissociation and oxidation reactions. DOCTOR OF PHILOSOPHY (SCBE)

Biomass is a carbon neutral renewable alternative to fossil fuels, and can help in reducing the demand for fossil fuels in the near future. This study is relevant to the liquid phase catalytic conversion of biomass to fuels, fuel additives and chemicals. Products obtained during the catalytic conversion can be used as platform chemicals for further upgradation to bulk chemicals, fuels and fuel additives. One such platform chemical is 5-hydroxymethylfurfural (HMF), which can be produced by the acid catalyzed dehydration of glucose, which is the largest monomeric component of lignocellulosic biomass. Recent research on the conversion of glucose to HMF has shown that the conversion and yield of the reaction are affected by the choice of solvents used. It has been noted that the solvents not only play the role of a benign solvation medium but also are involved in the conversion process and significantly affect the conversion and yield of the reaction. However, the exact role of solvents, as the reaction media, is not yet well understood. It would be extremely difficult to decouple physical solvation and chemical participation effects using experimental methods, so as to study them individually. To overcome this difficulty, computational modeling is used. The present work focuses on identifying key physical interactions between biomass molecules and solvents using molecular modeling. We perform molecular dynamics simulations, using OPLS/AA force field to investigate the physical solvation of glucose in four common solvents used in Biomass conversion studies, namely, water, Dimethylsulfoxide (DMSO), N,N-Dimethylformamide (DMF) and Tetrahydrofuran (THF). The parameters for the solvents were selected by careful consideration and were benchmarked with existing data from the literature to ensure accuracy. Force-field parameters for DMF, as reported in the literature with a negative partial charge on the amide nitrogen, resulted in poor prediction of the bulk properties like density and dielectric constant and showed reduced miscibility with water in a DMF-water mixed system. To address these issues, we proposed a new set of parameters with a small positive partial charge on the amide nitrogen. The new parameters were benchmarked with both, preexisting experimental data and using ab initio molecular dynamics, to ensure better accuracy of the DMF molecule. The local arrangement of solvents around the glucose molecule is analyzed using 2-dimensional radial pair distribution functions and 3-dimensional volumetric maps. Additionally, lifetimes and activation free energies of hydrogen bonds between solvents and glucose and the tendency of glucose molecules to agglomerate were studied. From our simulation studies and analysis it was observed that i) all the aforementioned co-solvents compete with water to be in the first solvation shell of glucose and significant amount of water is pushed to the second coordination shell; ii) though fewer water molecules are directly coordinated with glucose in the presence of co-solvents, they are bound strongly to it; iii) DMSO, THF and DMF tend to localize more around the hydrogen atom of the hydroxyl groups of selected carbon atoms of glucose; iv) the preferential arrangement of co-solvents and water around glucose may play a role in facilitating the reaction pathway for the formation of HMF and levulinic acid and may reduce the likelihood of glucose’ degradation to unwanted dehydration/rehydration products; v) Increasing the proportion of co-solvents also increases the hydrogen bond lifetimes between water and glucose and reduces the mobility of glucose molecules within the solvent. The reduced mobility of glucose molecules in the presence of co-solvents might be correlated to the experimentally observed reduction in the rate of formation of polymerization/condensation products and humins. MASTER OF ENGINEERING (SCBE)

With huge global natural gas reserves, coupled with depletion of fossil fuels, researchers are exploring potential technologies to convert methane into high value-added chemicals. Transition metal oxides (TMOs) are an important class of catalytic materials widely used in the direct and indirect catalytic methane conversion methods. Fundamental understanding of the reaction chemistry is crucial to the realization of commercial catalytic methane conversion processes. Computational tools like Density Functional Theory (DFT), and experimental surface characterization techniques like Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and X-ray Photoelectron Spectroscopy (XPS), are often used independently by computational and experimental researchers, to provide insights into metal oxide catalyzed reaction mechanisms, pathways, and energetics. Identifying realistic reaction intermediates and their corresponding IR and XPS spectral peaks presents a challenge for researchers to study complex catalytic reactions on TMO surfaces. DFT calculations are widely employed to assist in experimental analysis and provide mechanistic insights into reaction intermediates, and pathways for TMO catalyzed reactions. Localised nature of electrons leads to the strongly correlated nature of TMOs, and the standard approximations in the DFT exchange-correlation functional fail to describe these electron localizations accurately. DFT+U method is a widely used extension of DFT, where the Hubbard U term is an onsite potential that penalizes electron delocalization, successfully describing such systems. This U-value is usually chosen based on its accuracy in reproducing bulk properties, however, using the bulk properties-based U-values in a locally changing surface reaction environment may not describe the surface reaction energetics correctly. CuO is a widely-used TMO with applications in heterogeneous and environmental catalysis. In this thesis, two novel DFT+U approaches are developed with CuO as a model TMO and present methods for U-value determination that accurately capture the surface chemistry on TMOs. Both these approaches provide consistent U-values of 4-5 eV that accurately predicts the surface catalytic properties, as opposed to the widely used bulk property, optimized U-value of 7 eV that fails to correctly predict both surface reaction energetics and XPS shifts for CuO catalytic systems. In the first method, DFT+U calculations are performed to investigate the dissociative chemisorption of H2 on CuO, and the appropriate U-value is determined from the comparison of DFT+U calculated adsorption enthalpies for different U-values with the experimental adsorption enthalpy. In the second method, comparison of experimental XPS shifts with DFT+U derived XPS shifts (for a range of surface moieties on the catalyst) for different U-values leads to the determination of the U-value. The second method not only benchmarks the U-value but also establishes unknown surface adsorbates, their configurations and predict their experimental XPS shifts synergistically, thus addressing the bottlenecks associated with the application of integrated computational and experimental methods for studying TMO catalyzed reactions. After establishing a robust DFT+U method that accurately captures surface chemistry on TMOs, the sequential activation of C-H bonds of methane on CuO is investigated using DFT+U and experimental FTIR study. The primary process and operational challenges for methane catalytic conversion over TMO surfaces are associated with the activation of the highly stable and weakly polarized C-H bonds of methane, which leads to the employment of high operating temperatures, consequently favoring undesired reactions, leading to a loss in activity, selectivity, and yield of desired products. In literature, the presence of moisture and surface hydroxyls on transition metal systems is known to reduce the barriers of various catalytic methane conversion reactions, but their role in TMO catalyzed reactions has not been investigated. The current thesis reveals that the presence of surface hydroxide species on CuO reduces the activation barriers associated with methane activation and dissociation. Experimental FTIR study was performed to investigate the reaction under dry and moisturized reaction conditions and revealed the presence of similar intermediates (methoxy, formic, CO2, and surface hydroxyl species) under both conditions. Presence of surface hydroxide species even under dry conditions is predicted by DFT and confirmed by FTIR experiments, thus indicating that the C-H bond of methane may not be activated by CuO lattice oxygen directly but gets oxidized with the formation of moisture and surface hydroxide species, henceforth reducing the C-H activation barriers. In summary, this thesis reveals: (i) A novel surface reactivity based semi-empirical DFT+U approach that accurately describes surface catalytic reactions over TMOs and establishes the failure of widely applied bulk property optimized U-value to study these surface catalytic reactions, (ii) The Synergistic application of DFT and experimental XPS shifts to determine the reaction intermediates and surface species for TMO catalyzed reactions without any explicit knowledge of the U-value for respective TMO. This is the first study that integrates DFT and XPS methods to study TMO catalyzed reactions and addresses the bottleneck constraining the application of combined experimental and computational approaches to such systems. (iii) The promoting role of moisture and surface hydroxides in the activation and dissociation of methane from computational and experimental studies. This study provides evidence that even under dry conditions, lattice oxygen may not directly activate the C-H bonds of methane but indirectly via the formation of surface hydroxides formed on the surface. It also establishes that moisturized surface approach can lead to an increased lifetime of the catalysts due to water being the oxygen donor for the initial part of the methane activation. Doctor of Philosophy

Depletion of non-renewable sources has led to efforts in the development of technologies to utilize lignocellulosic biomass as a potential feedstock. One of the promising techniques to convert biomass to fuels is fast pyrolysis. Cellulose, a major component of biomass, is made of the β-D glucose rings attached by a β-1,4 glyosidic bond (C-O-C). Cleavage of the glycosidic bond is the first and an important reaction step in the decomposition of cellulose during fast pyrolysis. Experimental studies have shown that cellulose fragmentation undergoes two distinct cleavages - high activation barrier, possibly associated mid/intra-chain cleavage and low activation barrier, possibly associated end-chain scission. However, fundamental understanding and mechanistic insights into the two distinct kinetic regimes is completely lacking. Hence, in this study, the mechanistic and kinetic differences in mid and end-chain glycosidic bond cleavages in a condensed phase environment using periodic boundary conditions is investigated by mimicking the condensed environment observed experimentally during cellulose fragmentation. The activation barriers for different end and mid-chain scission mechanisms were calculated using cellotetraose as model compound and are also compared with those for cellulose and cellobioise. The end-chain scission enthalpic activation barriers are calculated were found to be lower than the mid-chain scission barriers by ~18.7 kcal mol-1, ~6.5 kcal mol-1 and ~5.1 kcal mol-1 for transglycosylation, glycosylation and ring contraction mechanisms for cellotetraose, respectively. This is in excellent agreement with the reported experimental studies showing different kinetic parameters regimes for different scission mechanisms. The difference between the end and mid chain scissions was attributed to the inter and intra molecular interactions that govern the relative stabilisation of the transition state. These interactions were interpreted using Reduced Density Gradient (RDG) plots. Energy decomposition analysis shows that the intermolecular interaction stabilizes end-chain scission, while mid-chain cleavage transition state is stabilized by intramolecular interactions. The magnitude of intermolecular interactions for end-chain cleavage was observed to be higher than intra-molecular interactions of mid-chain cleavage, leading to a more stable end-chain fragmentation transition state and lower C-O-C bond scission barriers. This observation was consistent when compared with cellobiose and cellulose glycosidic bond breaking. To the best of our knowledge, this is the first study providing mechanistic insights into end and mid-chain glycosidic bond cleavage and the need to incorporate intermolecular interactions while simulating pyrolysis reaction mechanisms using DFT. Master of Engineering (SCBE)