Effects of coverage on the structures, energetics, and electronics of oxygen adsorption on RuO2(110)

Synergistic effect of Ag(111) and transition metal promoters toward optimization of catalytic ethylene epoxidation selectivity

The ethylene epoxidation process is crucial for selective chemical oxidation in various industrial applications. However, adding suitable promoters improves the selectivity of the commercially available Ag-catalyzed ethylene epoxidation toward ethylene oxide (EO). Empirical evidence suggests that cesium can significantly enhance the modest selectivity of silver; however, there is a need for more effective dual or multi-promoter combinations to achieve better selectivity for EO. In the present study, we employ a density functional theory (DFT) approach to investigate the impacts of Cs and various transition metal (TM) promoters-Re, Rh, Au, Cu, W, Zn, and Mo-on the ethylene epoxidation. We analyze the electronic properties of the catalysts, the adsorption energies of the reactants, and the activation barrier energies associated with the intermediates, utilizing fundamental principles and transition state theory. The results indicate that an optimal charge balance on the catalyst can be attained by combining electron-accepting TMs with electron-donating Cs. This balance effectively suppresses the formation of nucleophilic oxygen species that would otherwise improve ethylene combustion. It also mitigates the excessive electrophilicy of Ag centers, which facilitates EO isomerization. Therefore, the overall selectivity toward EO is enhanced. Indeed, the findings and methodologies presented in this work illustrate that the multi-promoted catalyst (Ag/Cs22Cu24Re24Au30) can substantially improve the selectivity of the EO reaction, with a shift in selectivity from 1.29 to 2.71 eV when compared to the pristine Ag (111) catalyst.

Single-atom catalyst for high-performance methanol oxidation

Single-atom catalysts have been widely investigated for several electrocatalytic reactions except electrochemical alcohol oxidation. Herein, we synthesize atomically dispersed platinum on ruthenium oxide (Pt₁/RuO₂) using a simple impregnation-adsorption method. We find that Pt₁/RuO₂ has good electrocatalytic activity towards methanol oxidation in an alkaline media with a mass activity that is 15.3-times higher than that of commercial Pt/C (6766 vs. 441 mA mg^‒1_Pt). In contrast, single atom Pt on carbon black is inert. Further, the mass activity of Pt₁/RuO₂ is superior to that of most Pt-based catalysts previously developed. Moreover, Pt₁/RuO₂ has a high tolerance towards CO poisoning, resulting in excellent catalytic stability. Ab initio simulations and experiments reveal that the presence of Pt‒O_3f (3-fold coordinatively bonded O)‒Ru_cus (coordinatively unsaturated Ru) bonds with the undercoordinated bridging O in Pt₁/RuO₂ favors the electrochemical dehydrogenation of methanol with lower energy barriers and onset potential than those encountered for Pt‒C and Pt‒Ru.

It is still challenging to engineer single-atom catalysts for electrocatalytic methanol oxidation. Here, the authors design Pt single atom supported on RuO2 for highly active methanol oxidation in contrast to the inert Pt single atom supported on carbon.

Stable reconstruction of the (110) surface and its role in pseudocapacitance of rutile-like RuO2

Surfaces of rutile-like RuO₂, especially the most stable (110) surface, are important for catalysis, sensing and charge storage applications. Structure, chemical composition, and properties of the surface depend on external conditions. Using the evolutionary prediction method USPEX, we found stable reconstructions of the (110) surface. Two stable reconstructions, RuO₄-(2 × 1) and RuO₂-(1 × 1), were found, and the surface phase diagram was determined. The new RuO₄-(2 × 1) reconstruction is stable in a wide range of environmental conditions, its simulated STM image perfectly matches experimental data, it is more thermodynamically stable than previously proposed reconstructions, and explains well pseudocapacitance of RuO₂ cathodes.

A More Accurate Kinetic Monte Carlo Approach to a Monodimensional Surface Reaction: The Interaction of Oxygen with the RuO2(110) Surface

The theoretical study of catalysis would substantialy benefit from the use of atomistic simulations that can provide information beyond mean-field approaches. To date, the nanoscale understanding of surface reactions has been only qualitatively achieved by means of kinetic Monte Carlo coupled to density functional theory, KMC-DFT. Here, we examine a widely employed model for oxygen interaction with the RuO₂(110) surface, a highly anisotropic system. Our analysis reveals several covert problems that render as questionable the model’s predictions. We suggest an advanced approach that considers all the relevant elementary steps and configurations while smoothing the intrinsic errors in the DFT description of oxygen. Under these conditions, KMC provides quantitative agreement to temperature-programmed desorption experiments. These results illustrate how KMC-based simulations can be pushed forward so that they evolve toward being the standard methodology to study complex chemistry at the nanoscale.

Kinetic Monte Carlo simulations of heterogeneously catalyzed oxidation reactions

In this perspective, we focus on the catalyzed oxidation of CO and HCl over the model catalyst RuO₂(110) and how the kinetics of these reactions can only properly be modeled by kinetic Monte Carlo (kMC) simulations when lateral interactions of the surface species are taken into account.

Density functional theory for transition metals and transition metal chemistry

We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.