2024

Lempelto, Aku

In this dissertation, computational modelling methods based in density functional theory (DFT) were used to investigate the structure and adsorption characteristics of a heterogeneous catalytic system, consisting of zirconia-supported copper nanoparticles with a zinc oxide promoter (CZZ), that is used for carbon dioxide conversion to methanol (CTM). Supplementary analysis methods, such as the energetic span model and atomistic thermodynamics, were used to examine the stability and catalytic performance of the ternary Cu–Zn(O)–ZrO₂ interface. An extended screening was conducted to establish a suitable computational model for representing the metal–zirconia interface. Our results demonstrate how the specific internal geometry of a nanorod model and strains caused by lattice mismatch between Cu and ZrO₂ affect CO₂ adsorption at the interface, even leading to an overestimation of binding strength. The effect of Zn centres at the active interface sites was examined by using mixed CuZn interfaces and modelling the full catalytic network of CO₂ CTM using DFT and energetic span analysis. The calculated binding of reaction intermediates demonstrated how Zn incorporated into the catalyst metal selectively stabilizes certain species, such as CO₂, COOH and H₂CO. The energetic span analysis suggests that a reverse water–gas shift reaction followed by CO hydrogenation is the mechanistic pathway with the highest turnover frequency. An examination of ZnO monomers and sub-nano clusters on the zirconia surface suggests that the ZrO₂ support offers some resistance to the initial stages of agglomeration. An atomistic thermodynamics analysis suggests that the complete reduction of zirconia-bound ZnO into metallic Zn is unfavourable. Our results offer an atomic-level view of the behaviour of the ZnO promoter and its effect on CO₂ adsorption and conversion.