Mikrokinetično modeliranje katalitske pretvorbe ogljikovega dioksida v metanol : doktorska disertacija

slovenian

doktorska dela

2022

carbon dioxide conversion   Cu/ZnO/Al2O3   methanol synthesis   microkinetic modelling   structural-activity relationships

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

Reduction of greenhouse gas emissions into the atmosphere is key to maintaining the current state of the environment. At the same time, sustainable development requires the use of renewable raw materials and energy, so that we can avoid resource shortages and financial instability in the future. The purpose of the doctoral dissertation is to contribute to a faster transition to sustainable technologies, especially in the field of catalytic binding of carbon dioxide to more useful substances such as methanol. Knowledge of the behaviour of the catalyst structure and consequently of its activity is crucial due to the large amounts of emissions. Typically, kinetic models are constructed using the assumption of a single reaction path and the slowest step in the conversion. Microkinetic models in contrast include individual reaction steps at specific active sites of the surface, and therefore the structure and activity of the catalyst can be linked. Such a model is robust because it is based on a smaller number of assumptions and can be used to optimize the process with higher accuracy.The dissertation includes the study of the influence of the catalyst structure (and composition) on activity to describe the active sites for methanol synthesis. Based on these observations, the ab initio kinetics (or kinetics from the first principles) of a certain active site structure were selected and adjusted. Various characterization methods were used to determine the structure of the materials (N2O PSO-pulsed surface oxidation with N2O, STEM EDS-scanning electron microscopy with energy dispersive spectroscopy, XPS-X-ray photoelectron spectroscopy, XRD-X-ray powder diffraction with Rietveld analysis, N2 physisorption and many others).The main findings include the determination of the dynamics of Zn or ZnO on industrial Cu/ZnO/Al2O3 catalyst, which dictates the activity of the material. The impact of the key difference between CO2/H2 mixture conversion and the commercial fossil-based synthesis gas conversion process (mostly CO instead of CO2), was determined. This difference is the presence of the resulting water from CO2, which according to this study results in the deactivation of the catalyst through accelerated sintering of the Al2O3 phase. A catalyst deactivation model was developed, which is the first to link the influence of temperature, pressure and time on methanol synthesis activity. Structural-activity connections show that the activity of an industrial catalyst is influenced by several factors, the most important being the number of copper sites and the number of active zinc sites. Based on this, a microkinetic model based on Zn/Cu(211) kinetics and experimentally measured H2 adsorption kinetics on Cu was developed and includes the number of active Cu and Zn sites as parameters.The mechanism of CO2 conversion to Cu/SrTiO3 was additionally studied. The material combines important properties for efficient conversion and opens up new possibilities in the field of catalyst development.

07.08.2023