The main aim of this project was to optimize the conversion of 2,2', 4,4', 6,6' - hexanitrobibenzal (DPE) into 2,2', 4,4',6,6' - hexanitrostilbene (HNS). This was acheived in that conversions of greater than 90% were obtained when using salts of carboxylic acids as bases and oxygen as oxidant in dymethylsulphoxide solution. During the course of the work, studies of n.m.r spectra, reaction kinetics and electrochemistry provided convincing evidence that reaction proceeds via oxidation of the DPE monoanion which is in equilibrium with the more stable dianion and the substrate. It was also found possible to produce the DPE dianion by electrolytic reduction of HNS. In order to obtain more general information pertaining to the dehydrogenation of compounds of this type, a number of variously nitrosubstituted bibenzyls including naphthalene analogues, were prepared and their base induced dehydrogenations, in the presence of oxygen, studied. In general it was found that the substitution of nitro groups in ortho positions was disadvantageous except in the case of DPE itself. P,P' - Dinitrobibenzyl and 1,2-di-(4-nitro-1-naphthyl)ethane were found to be readily prepared and dehydrogenated in good yield using t-butoxide anion in dimethylsulphoxide solution under oxygen. In the former case, kinetic evidence was obtained which suggests that reaction proceeds via the dianion in contrast to the DPE.

Electrochemical CO2 reduction reaction (ECO2RR) powered by renewable electricity possesses the potential to store intermittent energy in chemical bonds while producing sustainable chemicals and fuels. Unfortunately, it is hard to achieve low overpotential, high selectivity, and activity simultaneously of ECO2RR. Developing efficient electrocatalysts is the most promising strategy to enhance electrocatalytic activity in CO2 reduction. Herein, we designed novel Bi-Cu2S heterostructures by a one-pot wet-chemistry method. The epitaxial growth of Cu2S on Bi results in abundant interfacial sites and these heterostructured nanocrystals demonstrated high electrocatalytic performance of ECO2RR with high current density, largely reduced overpotential, near-unity FE for formate production (Chapter 2). Meanwhile, we see a lot of opportunities for catalysis in a confined space due to their tunable microenvironment and active sites on the surface, leading to a broad spectrum of electrochemical conversion schemes. Herein, we reveal fundamental concepts of confined catalysis by summarizing recent experimental investigations. We mainly focus on carbon nanotubes (CNTs) encapsulated metal-based materials and summarize their applications in emerging electrochemical reactions, including ECO2RR and more (Chapter 3). Although we were able to obtain high activity and selectivity toward C1 products, it is more attractive to go beyond C1 chemicals to produce C2 products due to their high industrial value. Herein, we designed Ag-modified Cu alloy catalysts that can create a CO-rich local environment for enhancing C-C coupling on Cu for C2 formation. Moreover, Ag corporate in Cu can chemically improve the structural stability of Cu lattice. (Chapter 4) Nevertheless, advanced electrocatalytic platforms cannot be developed without a fundamental understanding of binding configurations of the surface-adsorbed intermediates and adsorbate-adsorbate interaction on the local environment in electrochemical CO2 reduction. In this case, we make discussions of recent developments of machine learning based models of adsorbate-adsorbate interactions, including the oversimplified linear analytic relationships, the cluster expansion models parameterized by machine learning algorithms, and the highly nonlinear deep learning models. We also discuss the challenges of the field, particularly overcoming the limitations of pure data driven models with the integration of computational theory and machine learning of lateral interactions for catalyst materials design. (Chapter 5). / Doctor of Philosophy / Excessive CO2 emissions into the atmosphere have had severe environmental impacts and pose an urgent and potentially irreversible threat to human activity. Fossil fuels, including coal, oil, and natural gas, have continued to play a dominant role in the global energy system. However, fossil fuels produce substantial greenhouse gases, which are the main contributor to global warming. This year, the global average CO2 level is increasing to 413.6 parts per million, higher than at any point in the past hundred years. To address this global warming issue, we see lots of opportunities to use alternative energy sources to convert atmospheric CO2 into value-added products through the electrochemical reduction of CO2. Nevertheless, advanced electrocatalytic platforms cannot be developed without efficient electrocatalysts in the reaction system. Therefore, we have been working on the design of catalysts with various features that improve the electrochemical reduction of CO2. The interface plays an important role as the reactions are happening at the active sites which mostly locate at the interface of electrocatalysts. We designed a novel Bi-Cu2S hetero-structured catalyst, which has abundant interfacial sites between Bi and Cu2S, demonstrating the improved catalytic performance of ECO2RR toward formate production (Chapter 2). Catalysis in a confined space offers another opportunity for tuning the catalytic performance, where carbon nanotubes (CNTs) encapsulated metal-based materials have been shown to increase the reactivity of electrochemical reactions, including ECO2RR and more (Chapter 3). Interfaces in alloys provide multifunctional environments which have been shown to have reactivity toward complicated reactions. To produce more value-added C2 chemicals, Ag-modified Cu alloy catalysts are developed, which can create a CO-rich local environment for enhancing C-C coupling on Cu to enhance C2 formation (Chapter 4). To develop advanced electrocatalytic platforms for CO2 electroreduction, it is essential to have a fundamental understanding of the binding configurations of surface-adsorbed intermediates and the adsorbate-adsorbate interaction within the local environment. In this regard, we discussed recent developments in machine learning-based models of adsorbate-adsorbate interactions for multiple electrochemical reactions (Chapter 5).

Hexagonal molybdenum nitride (δ-MoN) is one of the hardest superconductors, and its superconducting properties depend on the crystalline structure and the substrate of use. Herein, a versatile growth method has been utilized to grow single-crystalline (SC) δ-MoN thin films on any arbitrary substrate of interest. SC δ-MoN films have been achieved on amorphous substrates via the transfer of MoS2 precursors followed by chemical phase conversion. The transferred SC δ-MoN film on an amorphous SiO2/Si substrate exhibits superconductivity at Tc = 4.75 with an upper critical field Hc2(0) = 8.24 K. The effect of the transfer process was assessed by directly growing SC δ-MoN on an Al2O3 substrate, which showed enhanced superconductivity properties due to the nonuniformity in film thickness that the transfer process induces. The crystalline structure effect on superconductivity was studied by directly growing amorphous δ-MoN film on an amorphous SiO2/Si substrate. The amorphous film showed degraded superconducting behavior and confirmed that disorders in the crystal structure suppress superconductivity. The upper critical fields of the non-transferred δ-MoN films exceeded their Pauli paramagnetic limits, which could give rise to the existence of the Ising pairing effect, but further studies are needed to confirm this behavior.

As renewable energy production becomes more prevalent, the challenge of producing renewable dispatchable fuel for the transportation sector remains unresolved. One promising approach is to produce hydrogen from solar energy with a two step thermochemical cycle which utilizes an oxygen storage material (OSM) to split water through two reversible reactions. Due to the strong coupling between reactor design, operational parameters, and OSM properties, the direct comparison of two OSMs is not straightforward. In order to guide the designs of OSMs for two-step thermochemical hydrogen production, a methodology is developed to model the max performance possible for a two-step thermochemical cycle. The novel contribution of this model considers the strong coupling between reactor operation, OSM properties, and reactor performance. Next, a method for screening and evaluating new OSMs which utilizes thermogravimetric analysis (TGA) is proposed. With this data, the modeling method previously developed is applied to determine maximum reactor efficiency possible with new materials. This allows many materials to be evaluated quickly, and facilitates further characterization new OSMs. Additionally, by comparing the predicted maximum efficiency of a new material with the efficiency of current ones, this method facilitates the comparison of two different OSMs on equal footing.

The present work focuses on the study of biomass gasification process for generating hydrogen rich synthetic gas with oxy-steam as reactants using experiments and modeling studies. Utilization of the syngas as a fuel in general applications like fuel cells, Fischer-Tropsch FT) process and production of various chemicals like DME, etc. are being considered to meet the demand for clean energy. This study comprises of experiments using an open top down draft reactor with oxygen and steam as reactants in the co-current configuration. Apart from the standard gasification performance evaluation; parametric study using equivalence ratio, steam-to-biomass ratio as major variables towards generation of syngas is addressed towards controlling H2/CO ratio. The gasification process is modeled as a packed bed reactor to predict the exit gas composition, propagation rate, bed temperature as a function of input reactants, temperature and mass flux with variation in thermo-physical properties of biomass. These results are compared with the present experiments as well as those in literature. Experiments are conducted using modified open top downdraft configuration reactor with lock hoppers and provision for oxy-steam injection, and the exit gas is connected to the cooling and cleaning system. The fully instrumented system is used to measure bed temperatures, steam and exit gas temperature, pressures at various locations, flow rates of fuel, reactants and product gas along with the gas composition. Preliminary investigations focused on using air as the reactant and towards establishing the packed bed performance by comparing with the experimental results from the literature and extended the study to O2-N2 mixtures. The study focuses on determining the propagation rate of the flame front in the packed bed reactor for various operating conditions. O2 is varied between 20-100% (vol.) in a mixture of O2-N2 to study the effect of O2 fraction on flame propagation rate and biomass conversion. With the increase in O2 fraction, the propagation rates are found to be very high and reaching over 10 mm/s, resulting in incomplete pyrolysis and poor biomass conversion. The flame propagation rate is found to vary with oxygen volume fraction as XO22.5, and stable operation is achieved with O2 fraction below 30%. Towards introducing H2O as a reactant for enhancing the hydrogen content in the syngas and also to reduce the propagation rates at higher ER, wet biomass is used. Stable operating conditions are achieved using wet biomass with moisture-to-biomass (H2O:Biomass) ratio between 0.6 to 1.1 (mass basis) and H2 yield up to 63 g/kg of dry biomass amounting to 33% volume fraction in the syngas. Identifying the limitation on the hydrogen yield and the criticality of achieving high quality gas; oxy-steam mixture is introduced as reactants with dry biomass as fuel. An electric boiler along with a superheater is used to generate superheated steam upto 700 K and pressure in the range of 0.4 MPa. Steam-to-biomass ratio (SBR) and ER is varied with towards generating hydrogen rich syngas with sustained continuous operation of oxy-steam gasification of dry biomass. The results are analysed with the variation of SBR for flame propagation rates, calorific value of product syngas, energy efficiency, H2 yield per kg of biomass and H2/CO ratio. Hydrogen yield of 104 g per kg of dry casuarina wood is achieved amounting to 50.5% volume fraction in dry syngas through oxy-steam gasification process compared to air gasification hydrogen yield of about 40 g per kg of fuel and 20% volume fraction. First and second law analysis for energy and exergy efficiency evaluation has been performed on the experimental results and compared with air gasification. Individual components of the energy input and output are analysed and discussed. H2 yield is found to increase with SBR with the reduction in energy density of syngas and also energy efficiency. Highest energy efficiency of 80.3% has been achieved at SBR of 0.75 (on molar basis) with H2 yield of 66 g/kg of biomass and LHV of 8.9 MJ/Nm3; whereas H2 yield of 104 g/kg of biomass is achieved at SBR of 2.7 with the lower efficiency of 65.6% and LHV of 7.4 MJ/Nm3. The energy density of the syngas achieved in the present study is roughly double compared to the LHV of typical product gas with air gasification. Elemental mass balance technique has been employed to identify carbon boundary at an SBR of 1.5. Controlling parameters for arriving at the desired H2/CO ratio in the product syngas have been identified. Optimum process parameters (ER and SBR) has been identified through experimental studies for sustained continuous oxy-steam gasification process, maximizing H2 yield, controlling the H2/CO ratio, high energy efficiency and high energy density in the product syngas. Increase in ER with SBR is required to compensate the reduction in O2 fraction in oxy-steam mixture and to maintain the desired bed temperature in the combustion zone. In the range of SBR of 0.75 to 2.7, ER requirement increases from 0.18 to 0.3. The sustained continuous operation is possible upto SBR of 1.5, till the carbon boundary is reached. Operating at high SBR is required for high H2 yield but sustained highest H2 yield is obtained as SBR of 1.5. H2/CO ratio in the syngas increases from 1.5 to 4 with the SBR and depending on the requirement of the downstream process (eg., FT synthesis), suitable SBR and ER combination is suggested. To obtain high energy density in syngas and high energy efficiency, operations at lower SBR is recommended. The modeling study is the extension of the work carried by Dasappa (1999) by incorporating wood pyrolysis model into the single particle and volatile combustion for the packed bed of particles. The packed bed reactor model comprises of array of single particles stacked in a vertical bed that deals with the detailed reaction rates along with the porous char spheres and thermo-physical phenomenon governed by the mass, species and energy conservation equations. Towards validating the pyrolysis and single particle conversion process, separate analysis and parametric study addressing the effects of thermo-physical parameters like particle size, density and thermal conductivity under varying conditions have been studied and compared with the available results from literature. It has been found that the devolatilisation time of particle (tc) follows closely the relationship with the particle diameter (d), thermal conductivity (k), density () and temperature (T) as: The complete combustion of a single particle flaming pyrolysis and char combustion has been studied and validated with the experimental results. For the reactor modeling, energy, mass and species conservation equations in the axial flow direction formulate the governing equations coupled to the detailed single particle analysis. Gas phase reactions involving combustion of volatiles and water gas shift reaction are solved in the packed bed. The model results are compared with the experimental results from wood gasification system with respect to the propagation rate, conversion times, exit gas composition and other bed parameters like conversion, peak bed temperatures, etc. The propagation rates compare well with experimental data over a range of oxygen concentration in the O2- N2 mixture, with a peak at 10 mm/s for 100 % O2. In the case of oxy-steam gasification of dry biomass, the results clearly suggest that the char conversion is an important component contributing to the bed movement and hence the overall effective propagation rate is an important parameter for co-current reactors. This is further analyzed using the carbon boundary points based on elemental balance technique. The model predictions for the exit gas composition from the oxy-steam gasification matches well with the experimental results over a wide range of equivalence ratio and steam to biomass ratio. The output gas composition and propagation rates are found to be a direct consequence of input mass flux and O2 fraction in oxy-steam mixture. The present study comprehensively addresses the oxy-steam gasification towards generating hydrogen rich syngas using experimental and model studies. The study also arrives at the parameters for design consideration towards operating an oxy-steam biomass gasification system. The following flow chart provides the overall aspects that are covered in the thesis chapter wise.