Effect of plasma-induced surface charging on catalytic processes: application to CO₂activation

Abstract

Understanding the nature and effect of the multitude of plasma-surface interactions in plasma catalysis is a crucial requirement for further process development and improvement. A particularly intriguing and rather unique property of a plasma-catalytic setup is the ability of the plasma to modify the electronic structure, and hence chemical properties, of the catalyst through charging, i.e., the absorption of excess electrons. In this work, we develop a quantum chemical model based on density functional theory (DFT) to study excess negative surface charges in a heterogeneous catalyst exposed to a plasma. This method is specifically applied to investigate plasma-catalytic CO2 activation on supported M/Al2O3 (M = Ti, Ni, Cu) single atom catalysts. We find that (1) the presence of a negative surface charge dramatically improves the reductive power of the catalyst, strongly promoting the splitting of CO2 to CO and oxygen, and (2) the relative activity of the investigated transition metals is also changed upon charging, suggesting that controlled surface charging is a powerful additional parameter to tune catalyst activity and selectivity. These results strongly point to plasma-induced surface charging of the catalyst as an important factor contributing to the plasma-catalyst synergistic effects frequently reported for plasma catalysis.

Fundamental Properties and Applications of Dielectric Barrier Discharges in Plasma‐Catalytic Processes at Atmospheric Pressure

“…However, plasma-induced modification of the electronic properties may lead to new catalyst systems. Bal et al [71] investigated supported single-atom catalysts containing Ti, Ni or Cu and reported based on a quantum-chemical model that negative surface charges not only improve the reductive potential of the catalysts, but also change their relative activity. Furthermore, the trapped surface charges initiate the formation of streamers as the trapped surface charges are released by photons emitted from a single filament [72].…”

Plasma-catalysis: Is it just a question of scale?

“…It is also possible that the addition of electrons can affect the bonding between a molecular adsorbate and the surface creating repulsive interactions leading to desorption. Bal et al [53] have used density functional theory to look at the effect of negative surface charging of a catalyst exposed to a plasma. They examined the activation of CO 2 on transition metal/alumina catalysts finding that the charging significantly enhances the dissociation of the CO 2 to CO by improving the reductive power of the metal and that the magnitude of this effect differs for different metals.…”

Activation of CO2 on Copper Surfaces: The Synergy between Electric Field, Surface Morphology, and Excess Electrons

“…Using density functional theory (DFT) calculations, we have already shown that the presence of excess electrons improves the activation of CO2 on supported transition metal clusters 21,22 . In these works, however, we did not attempt to disentangle the role of electric field and surface charge.…”