Surface activation by electron scavenger metal nanorod adsorption on TiH2, TiC, TiN, and Ti2O3

Propane dehydrogenation catalysis of group IIIB and IVB metal hydrides

Catalytic propane dehydrogenation (PDH) has mainly been studied using metal- and metal oxide-based catalysts. Studies on dehydrogenation catalysis by metal hydrides, however, have rarely been reported. In this study, PDH reactions using group IIIB and IVB metal hydride catalysts were investigated under relatively low-temperature conditions of 450 °C. Lanthanum hydride exhibited the lowest activation energy for dehydrogenation and the highest propylene yield. Based on kinetics studies, a comparison between the reported calculation results and isotope experiments, the hydrogen vacancies of metal hydrides were involved in low-temperature PDH reactions.

Prediction of Stable Surfaces of Metal Oxides through the Unsaturated Coordination Index

This study proposes the unsaturated coordination index, σ, as a potential descriptor of the stability of metal-oxide surfaces cleaved from bulk. The value of σ, the number of missing bonds per unit area, can be obtained very quickly using only crystallographic data, namely, the bulk geometry. The surface energies of various binary oxides, with and without atom relaxation, were calculated. Their correlations with σ had good coefficients of determination (R2) values, particularly in high-symmetry crystals. The proposed descriptor is very useful for an initial evaluation of stable metal-oxide surfaces without conducting any surface model calculations.

Trends in Surface Oxygen Formation Energy in Perovskite Oxides

Perovskite oxides comprise an important class of materials, and some of their applications depend on the surface reactivity characteristics. We calculated, using density functional theory, the surface O vacancy formation energy (E _Ovac) for perovskite-structure oxides, with a transition metal (Ti-Fe) as the B-site cation, to estimate the catalytic reactivity of perovskite oxides. The E _Ovac value correlated well with the band gap and bulk formation energy, which is a trend also found in other oxides. A low E _Ovac value, which is expected to result in higher catalytic activity via the Mars-van Krevelen mechanism, was found in metallic perovskites such as CaCoO₃, BaFeO₃, and SrFeO₃. On the other hand, titanates had high E _Ovac values, typically exceeding 4 eV/atom, suggesting that these materials are less reactive when O vacancy formation is involved in the reaction mechanism.

Understanding and controlling the formation of surface anion vacancies for catalytic applications

Systematic computational efforts aimed at calculating surface anion vacancy formation energies as important descriptors of catalytic performance are summarized.

Factors determining surface oxygen vacancy formation energy in ternary spinel structure oxides with zinc

Spinel oxides are an important class of materials for heterogeneous catalysis including photocatalysis and electrocatalysis. The surface O vacancy formation energy (E_Ovac) is a critical quantity for catalyst performance because the surface of metal oxide catalysts often acts as a reaction site, for example, in the Mars-van Krevelen mechanism. However, experimental evaluation of E_Ovac is very challenging. We obtained the E_Ovac for (100), (110), and (111) surfaces of normal zinc-based spinel oxides ZnAl₂O₄, ZnGa₂O₄, ZnIn₂O₄, ZnV₂O₄, ZnCr₂O₄, ZnMn₂O₄, ZnFe₂O₄, and ZnCo₂O₄. The most stable surface is (100) for all compounds. The smallest E_Ovac for a surface is the largest in the (100) surface except for ZnCo₂O₄. For (100) and (110) surfaces, there is a good correlation, over all spinels, between the smallest E_Ovac for the surface and bulk formation energy, while the ionization potential correlates well in (111) surfaces. Machine learning over E_Ovac of all surface sites in all orientations and for all compounds to find the important factors, or descriptors, that decide the E_Ovac revealed that bulk and surface-dependent descriptors are the most important, namely the bulk formation energy, a Boolean descriptor of whether the surface is (111) or not, and the ionization potential, followed by geometrical descriptors that are different in each O site.