Nonthermalized Precursor-Mediated Dissociative Chemisorption at High Catalysis Temperatures.

Quasiclassical trajectory calculations and vibrational-state-selected beam-surface measurements of CH4 chemisorption on Ir(111) reveal a nonthermal, hot-molecule mechanism for C-H bond activation. Low-energy vibrationally excited molecules become trapped in the physisorption well and react before vibrational and translational energies accommodate the surface. The reaction probability is strongly surface-temperature-dependent and arises from the pivotal role of Ir atom thermal motion. In reactive trajectories, the mean outward Ir atom displacement largely exceeds that of the transition-state geometry obtained through a full geometry optimization. The study also highlights a new way for (temporary) surface defects to impact high-temperature heterogeneous catalytic reactivity. Instead of reactants diffusing to and competing for geometrically localized lower barrier sites, transient, thermally activated surface atom displacements deliver low-barrier surface reaction geometries to the physisorbed reactants.

Assessment of van der Waals inclusive density functional theory methods for layered electroactive materials.

The discovery of computationally driven materials requires efficient and accurate methods. Density functional theory (DFT) meets these two requirements for many classes of materials. However, DFT-based methods have limitations. One significant shortcoming is the inadequate treatment of weak van der Waals (vdW) interactions, which are crucial for layered materials. Here we assess the performance of various vdW-inclusive DFT approaches for predicting the structure and voltage of layered electroactive materials for Li-ion batteries, considering a set of 20 different compounds. We find that the so-called optB86b-vdW density functional improves the agreement with the experimental data, closely followed by the latest generation of dispersion correction methods. These approaches yield average relative errors for the structural parameters smaller than 3%. The average deviations for redox potentials are below 0.15 V. Looking ahead, this study identifies accurate methods for Li-ion vdW bound systems, providing enhanced predictive power to DFT-assisted design for developing new types of electroactive materials in general.

Lowering energy barriers in surface reactions through concerted reaction mechanisms.

Any technologically important chemical reaction typically involves a number of different elementary reaction steps consisting of bond-breaking and bond-making processes. Usually, one assumes that such complex chemical reactions occur in a step-wise fashion where one single bond is made or broken at a time. Using first-principles calculations based on density functional theory we show that the barriers of rate-limiting steps for technologically relevant surface reactions are significantly reduced if concerted reaction mechanisms are taken into account.