Dongjae Shin (신동재)

Catalyst design with good stability beyond simply having high activity is crucial for a variety of reactions. Here, we evaluate the ceria catalyst for CO oxidation as a model reaction to rationally design an ultrastable catalyst with high activity. The goal was achieved by co-doping with rare-earth (RE) and transition metals (TM) simultaneously. The RE dopant stabilized the catalyst by inhibiting sintering that could lead to catalyst deactivation. The TM dopant increased the activity by facilitating formation of surface defects. Consequently, ceria co-doped with RE (=La, Sm) and TM (=Cu) had increased catalytic activity as well as superior resistance to deactivation during 10 cycle measurement (1 cycle: 900 °C, 24 h → cooling at room temperature → target °C, 24 h) of ∼700 h, which is harsher than any other reported conditions. This approach will shed light on the design of ultrastable oxide materials for a wide range of catalytic reactions.

The water–gas shift reaction (WGSR) is important in industries because it can reduce the CO content of syngas to produce purified H2, which can be used as fuel or to make ammonia (NH3). Supported noble metal catalysts have been widely studied for the WGSR because they exhibit high reactivity. However, the role of a metal–support interface in the WGSR has not yet been revealed and remains elusive. Density functional theory (DFT) calculations were performed for a model system of Co3O4-supported Pd (Pd/Co3O4) catalysts. The presence of the interface was found to promote the H2O dissociation step, which is crucial for improving WGSR activity. Thus, the WGSR activity was predicted to be enhanced by an increased number of interfaces, which could be achieved by controlling the size of the supported Pd nanoparticles (NPs). Furthermore, electronic metal–support interactions (MSIs) were found to be a source of the promoted H2O dissociation at the interface. The DFT-predicted promotion of H2O dissociation was further experimentally validated using Pd/Co3O4 catalysts that were size-controlled with calcination temperatures, and the total length of the interface was shown to have a direct correlation with the WGSR rate. Theoretical insights into the role of the interface and the enhancement of WGSR activity due to increased interface sites, which can be achieved by size control, are believed to be useful in the design of efficient supported metal catalysts for the WGSR.

Oxidation of elemental Hg (Hg0) is catalytically and economically an efficient way to remove the harmful Hg contained in the flue gas from coal combustion facilities. Thus, the development of a highly active V2O5/TiO2 catalyst, which is active to the Hg oxidation, is very essential. Support modification can change the reactivity of V2O5/TiO2 by affecting the V2O5 active center which is critical to the surface–reactant interaction, so understanding the effects of support tuning methods, e.g., crystallographic phase control and reduction treatment, on the Hg oxidation activity is valuable. Herein, density functional theory calculations were performed to mechanistically investigate the change of Hg oxidation reactivity by the support tuning methods and to elucidate the change of the electronic environment at the active site. The phase control to the TiO2 support was found to improve the Hg oxidation activity, but the reduction treatment decreased the activity, which is attributed to the change of the charge density at V2O5. Furthermore, the origin of the reactivity change was elucidated within a Sabatier-like principle that the interaction between the V site and the surface Cl critically contributes to the change of the Hg oxidation reactivity by balancing the competition between two key reaction steps of HCl dissociation and HgCl2 desorption. Our results provide guidance to improve the activity of the VOx/TiO2 catalyst for various reactions such as Hg oxidation and selective catalytic reduction of NOx and so on.