Theoretical Studies on the Influence of Size and Support Interactions of Copper Catalysts for CO2 Hydrogenation to Methanol

Global warming and climate change, caused by greenhouse gases (GHG) released into the atmosphere by human activities, are becoming one of the world’s most crucial issues. Carbon dioxide (CO2) is the primary emitted greenhouse gas, produced mostly from the usage of fossil fuels. The daily increase in the global energy demand and the promising potential of converting and using the captured emitted CO2 to value-added products and chemicals (e.g., methanol) resulted in a vast amount of inventions and investigations on this topic. Methanol is the simplest alcohol and one of the valuable converted products of the CO2 conversion process, which can be used as renewable energy, fuels, etc. In industry, methanol is synthesized through heterogeneous catalytic reactions utilizing Cu-based catalysts, promoted or unpromoted nanoparticles (NPs) on support materials. Theoretical and computational methods of modelling heterogeneous catalytic reactions, done mostly by applying density functional theory (DFT) methods, are one example of benefiting from computer-aided material designing. However, investigating this procedure is challenging as the difference in the size scale of the study systems between the experiments and theoretical works are different. ... mehrDFT is perfectly capable of handling systems consisting of a few hundred atoms, which contrasts with real systems with thousands of atoms.
In this thesis, by applying cost-efficient and, at the same time, highly accurate computational models, some critical challenges regarding the procedure of converting CO2 to methanol, such as the catalyst’s particle size and shape effect, support effect, and applications of trends in catalytic reactions, were investigated. The utilization of DFT provided a fundamental understanding of the properties of the transition metal (TM) catalysts, with sizes ranging from 0.5 nm to 3.6 nm, using their fixed geometries and the adsorption energies of the intermediates related to methanol synthesis as descriptors. In addition, after confirming the reliability of the proposed models for different transition metals, the influence of the supports, inert (graphene) and oxide (magnesium oxide (MgO)), on the properties of NPs, through adsorption studies with different sizes and shapes was determined.
Moreover, the development of the models mentioned paved the way toward finding the trends in catalytic reactions through linear scaling relationships between the adsorption energies of the intermediates involved in methanol synthesis. In addition to the linear scaling relationships in the adsorption energies, the important role of geometrical and electronic effects affecting these relations is also demonstrated.
Finally, the origin of the copper particle size effect, which plays a significant role in CO2 hydrogenation to methanol and its competitor reverse water gas shift reaction (RWGS), is demonstrated as the reaction being clearly structure sensitive and providing a new guideline in designing of novel catalysts for methanol synthesis from CO2.