Plasma-enhanced catalytic reduction of SO2: Decoupling plasma-induced surface reaction from plasma-phase reaction

Abstract

Complex processes take place when coupling nonthermal plasma with heterogenous catalysis, obscuring mechanistic understanding of the plasma–catalysis synergy. Simultaneous homogenous plasma-phase reactions and heterogenous surface catalytic reactions occur in the system, which makes distinguishing the plasma’s contributions very challenging. In this work, we perform a careful and rigorous evaluation of surface reactions under plasma conditions. We use SO2 hydrogenation as a probe reaction to examine plasma-induced surface reactions, desorption, and dissociation of SO2 adsorbate. A temperature-programmed plasma-induced surface reaction approach is used to decouple plasma-induced surface reactions from plasma-phase reactions. The qualitative and quantitative analyses reveal a new Eley-Rideal reaction between plasma-generated atomic hydrogen in the gas-phase and strongly adsorbed SO2 over alumina, a reaction that is not thermally feasible. Furthermore, plasma causes partial desorption of weakly adsorbed SO2 species and enhances the strong chemisorption of SO2 over supported iron sulfide catalyst. Moreover, plasma facilitates H2 chemisorption and reaction with iron sulfide, producing sulfur vacancies. This work sheds light on the possible origin of plasma–catalysis synergy and offers fundamental insight about the underlying mechanisms of plasma-assisted SO2 hydrogenation reaction.