High CO₂ conversion via plasma assisted reverse water-gas shift reaction over Ag/ZnO catalyst

Reverse water-gas shift reaction represents a strategic pathway for CO₂ utilization. Despite its potential, reverse water-gas shift reaction via conventional thermal-catalysis faces several challenges. Now, a study published in Frontiers of Chemical Science and Engineering shows how non-thermal plasma (NTP) combined with a Ag/ZnO catalyst overcomes these limitations.

The research team synthesized the Ag/ZnO catalyst using a co-precipitation method. When tested in a dielectric barrier discharge (DBD) reactor, the plasma + Ag/ZnO system showed dramatic improvement. In contrast, the plasma alone system achieved only 21.8% CO₂ conversion, while the inclusion of ZnO alone did not improve performance.

X-ray photoelectron spectroscopy and Auger electron spectroscopy results confirm the presence of electronic metal-support interactions between Ag and ZnO. These interactions facilitate the formation of electron-deficient Ag sites and partially reduced ZnO species. Temperature-programmed desorption experiments showed that Ag/ZnO has enhanced ability for H₂ and CO₂ adsorption and activation compared to ZnO.

The researchers attribute the excellent performance to a dominant plasma-assisted surface reaction pathway. The electron-deficient Ag sites enhance H₂ dissociation and spillover, while oxygen vacancies and reduced ZnOₓ species on the catalyst surface effectively adsorb and activate CO₂. The plasma then drives the surface reaction between these activated species.

The system demonstrated stable operation over 6h, maintaining ~76.5% CO₂ conversion and ~96.8% CO selectivity. The energy efficiency of 0.19 mmol·kJ⁻¹ in the plasma + Ag/ZnO system represents nearly a 4-fold improvement over the plasma alone and plasma + ZnO conditions.

This work underscores the crucial role of electronic metal-support interactions in manipulating surface environments for efficient plasma-assisted catalytic reactions. The findings offer significant implications for the rational design of catalysts capable of converting CO₂ efficiently under mild conditions.