Chemical reactions under cover – a sneak peek

In this paper, using density functional theory (DFT) based ab initio molecular dynamics (AIMD), we showed that 2-dimensional confinement, manifested in the form of a graphene layer, can enhance CO oxidation reaction on a platinum surface substantially at lower temperatures than at high temperatures. If realised experimentally at a large scale, we could carry out oxidation of toxic CO at low temperatures that would be sustainable and environmentally beneficial.

Accelerating chemical reactions using heterogeneous catalysts plays a major player in attaining a sustainable future. Chemical reactions at surfaces on clean metal surfaces have been the prototypes for studying the mechanism of heterogeneous catalytic reactions at the molecular level. In these types of reactions, molecule/s in the gas phase interact/s with the catalyst in the solid phase to form product/s. Most heterogeneous catalytic reactions are thermally driven in which a reaction is accelerated with an increase in temperature. However, an interesting question was posed to the community a decade ago. Can chemical reactions at surfaces be accelerated in the presence of a 2-dimensional (2D) layer, like graphene, for example? The 2D cover, like graphene, provides a confined environment, wherein the reactant molecules are sandwiched between the catalyst surface and the 2D layer (cover image). This special interface was experimentally shown to accelerate chemical reactions compared to those at surfaces without 2D confinement. For example, in reactions like CO oxidation on a platinum surface, where a harmful CO (carbon monoxide) is converted to less harmful CO2 (carbon dioxide).

Energetics and electronic structure information obtained using static DFT has been widely used to understand the effect of 2D cover on these types of reactions. However, these DFT calculations are limited to providing only a static picture. Moreover, the effect of temperature is not included in these calculations. Since the active sites of catalysts in these types of reactions are dynamic, a dynamics simulation that includes the effect of temperature is necessary. To this aim, using DFT-based AIMD simulations, for the first time, we show that the effect of 2D confinement is profound at lower temperatures (90 K) compared to higher temperatures (593 K). We believe this study would motivate further studies in operando modelling of heterogeneous catalytic reactions under confined environments.