Mechanistic insights into heterogeneous methane activation

Abstract

While natural gas is an abundant chemical fuel, its low volumetric energy density has prompted a search for catalysts able to transform methane into more useful chemicals. This search has often been aided through the use of transition state (TS) scaling relationships, which estimate methane activation TS energies as a linear function of a more easily calculated descriptor, such as final state energy, thus avoiding tedious TS energy calculations. It has been shown that methane can be activated via a radical or surface-stabilized pathway, both of which possess a unique TS scaling relationship. Herein, we present a simple model to aid in the prediction of methane activation barriers on heterogeneous catalysts. Analogous to the universal radical TS scaling relationship introduced in a previous publication, we show that a universal TS scaling relationship that transcends catalysts classes also seems to exist for surface-stabilized methane activation if the relevant final state energy is used. We demonstrate that this scaling relationship holds for several reducible and irreducible oxides, promoted metals, and sulfides. By combining the universal scaling relationships for both radical and surface-stabilized methane activation pathways, we show that catalyst reactivity must be considered in addition to catalyst geometry to obtain an accurate estimation for the TS energy. This model can yield fast and accurate predictions of methane activation barriers on a wide range of catalysts, thus accelerating the discovery of more active catalysts for methane conversion.

Identifying promising metal–organic frameworks for heterogeneous catalysis via high‐throughput periodic density functional theory

“…When studying materials such as MOFs with spatially isolated active sites, the expected mechanism for the conversion of methane to methanol is the radical‐rebound mechanism, as shown in Figure . For HT screening purposes, we focus on the oxidation of the metal and H‐abstraction steps of this mechanism, as they dictate the overall conversion of methane by influencing the number of metal oxide active sites and the activity of each site, respectively.…”

Selective Activation of Methane C-H Bond in the Presence of Methanol

“…Brønsted-Evans-Polanyi or transition state scaling type of relation), [11] we found that such scaling relation is not applicable in our case, i.e., the uncertainty in the linear correlation is larger than what is practical ( Fig. S4), presumably because for single-atom catalysts the properties of the active single-site are very sensitive to the TM element and its immediate neighborhood.…”

Catalytic Oxidation of Methane: Pd and Beyond

“…the differences in the complexity of models and real catalytic systems), aiding in the selection of promoters, the indication of the active phases, and for modeling reaction kinetics . We believe that a combination of powerful tools of rapid computational screening, advanced synthetic methods for nanostructural control [e.g. Atomic Layer Deposition (ALD)] and operando characterization techniques can make important contributions to unraveling structure/activity relationships and design better methane oxidation catalysts.…”