In-situ regeneration of Au nanocatalysts by atmospheric-pressure air plasma: Significant contribution of water vapor

• In-situ and rapid regeneration of Au catalysts is achieved by humid air plasma.
• Regeneration degree depends strongly on water vapor content in air plasma.
• Water vapor speeds up carbonate species decomposition on the deactivated catalysts.
• Water vapor inhibits nitrogen oxides formation during air plasma regeneration.

In-situ regeneration of deactivated Au nanocatalysts during CO oxidation, was conducted effectively by pure oxygen plasma, but poisoned by dry air plasma in our previous work (Appl. Catal. B2012, 119–120, 49–55). With extension of previous study, a simple and effective technique of atmospheric-pressure cold plasma of humid air is explored for in-situ regeneration of Au nanocatalysts. In comparison with ineffective regeneration by dry plasma, humid plasma using synthetic air (20% O2 balance N2) as discharge gas surprisingly exhibited effective regeneration performance over Au catalyst due to significant contribution of water vapor. After plasma regeneration for 5 min, the regeneration degree of Au catalysts significantly increased up to 98% under humid plasma in presence of 2.77 vol.% water, while decreased down to negative 29% under dry plasma. To disclose the mechanism of water vapor contribution to greatly improved regeneration degree, the characterizations of regenerated catalysts, and the analyses of electric discharge characteristics and gaseous products during the plasma regeneration were conducted. The significant contribution of water vapor embodies in that it speeds up the decomposition of carbonate species and simultaneously inhibits the formation of poisoning species of nitrogen oxides. Furthermore, normal air instead of synthetic air in humid plasma regeneration was implemented on the evaluations of the deactivated Au catalysts after a long-term reaction and during ten deactivation-regeneration cycles, which ensured the feasibility and reliability of in-situ plasma regeneration of Au nanocatalysts as a simple, effective and promising technique.

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