Density Functional Theory Study On The Electronic Effects And Geometric Effects Of Metal And Metal Oxide Materials In Clean Energy Production

Due to the increasing world population and rapid development of many nations, the worldwide demand for energy has never been higher and is increasing. The vast majority of energy is currently produced from fossil fuels, readily available supplies of which are limited and the waste products from their burning are linked with dramatic environmental damage. The research of alternate sources of energy, such as wind and solar, has become a hot topic during recent decades. With advancements such as high combustion heat, wide-ranging usage and no pollution, especially for it could build a carbon free cycle, hydrogen has been believed to play an important role in the future energy landscape. Fuel cells using formic acid as their hydrogen sources are thought to be a practical solution to the stroage, transportation and application of hydrogen energy. In recent years, carbon dioxide (CO2) which is one of the main greenhouse gases has attracted public attention due to the implication of its emissions on climate change. Various sequestration technologies for CO2abatement are being considered and using chemical methods it could be transform to source of energy or some other raw materials. There is recognition that CO2hydrogenation to generate methanol provides a promising approach to the recycling of CO2and substitution of fossil fuel route. It also presents a significant prospect in transform, storage and transportation of hydrogen. In these two targeting reactions of formic acid decomposition and CO2hydrogenation to methanol, heterogeneous catalysts play an crucial role. The electronic effect, geometric effect and metal-support interaction are determining elements of the catalysis reactivity and mechanisms. However, it is quite difficult to understand these important effects in micro scale. In this thesis, we will make a systematical study into the metal and metal oxide catalyst used in these two reactions combining DFT calculations and experimental results. Firstly, through a combined approach of experimental and computational results we have presented a substantial electronic modification from a range of polymer stablizers to Pd nanoparticles. The electronic donation from PA amine to Pd appears to be very strong. This could be demonstrated by the coadsorbed CO vibration. Meanwhile, corresponding to the activity and adsorption mode,a significant geometric modification is also found, with amine containing polymers showing selective blockage of low coordinate sites and polymers with two heteroatoms blocking terrace sites. This geometric effect might change the selectivity or the overall route of the reaction. From this assumption, we further calculated the decomposition mechanisms of formic acid on flat and stepped Pd surface. We found that the targeting products CO2and H could be produced from dual routes of O-H and C-H cleavage. These two processes are thermaldynamically and kinetically favourable on both flat and stepped surface. The energy barriers of initial CO generation are obviously higher on these two surfaces, indicating that CO should be a minor byproduct which is consistent with the experiment. Meanwhile, this side reaction is relatively more facil on stepped site, which is the main cause of metal catalyst poisioning. On the other hand, combining experimental characterizations and DFT calculation, we have studied two shapes of Ga2O3particles with different dominant facets. In these materials the nanorod mainly exposes the Ga2O3(111) while the nanoplate exhibits the Ga2O3(001) surface, which has two surface terminations. The Ga2O3(001)-A termination gives the lowest vacancy formation energy while it is higher on Ga2O3(001)-B than Ga2O3(111). This is decided by the change of surface Ga or O atoms coordinations and rearrangements and consistent with TEM and EPR results. The Pd loaded nanoplate presents a stronger metal-support interaction(SMSI) and more active sites in CV and CO stripping tests. Using a simplified dopant model, the SMSI has been studied and the Ga2O3(001)-A termination still keeps the lowest dope energy and vacancy formation energy as its structure is more favourable to stablize the Pd dopant. The adsorption of reactants and intermediates are calculated. CO2could be adsorbed moderately and activited by electron transfer on Ga2O3(001)-A and Ga2O3(111). The detailed initial steps of CO2hydrogenation to bicarbonate species on these two surfaces are also compared and it is more facil on Ga2O3(001)-A. As the structure and energy of intermediates are quite similar on these two surfaces, the reaction route should be close and the activation of CO2must be a deciding step, which is also the origin of the outstanding catalysis performance of nanoplate dominated by Ga2O3(001).