Towards the Understanding of Parameters Allowing to Anticipate the Precipitation Reaction of Metallic Precursors in Humid Air Gliding Arc Plasma Reactor

Abstract

The humid air gliding arc plasma (GP) has demonstrated its capability to synthesize catalysts (metal (hydr)oxides and supported catalysts) with intriguing properties and significant catalytic activity while employing interesting synthesis conditions compared to conventional catalyst synthesis. However, previous studies exposed various precursors to the plasma without prior knowledge of their reactivity through GP. The objective of this paper is to investigate the parameters influencing precursor reactivity and precipitation under humid air GP, by identifying commonalities between reactive and non-reactive precursors. Several factors were identified as predominant: the solubility of the precursor and precipitate, the acidification of the medium along exposure, the redox potential of reactions between the precursor and HNO₂/NO₂⁻ species plasma-generated, and the metal precursor nature. These identified factors have enabled us to create a dichotomous key that can be used for any type of precursors, allowing to anticipate their potential precipitation when exposed to the GP. By utilizing this key, we have identified two new precursors that react, forming new types of solids never synthesized before by GP: Au and Ru-based solids. This demonstrates that GP may be a promising method for developing new types of catalysts, such as metal-supported catalysts, but also indicates that a limited number of precursors may react, at least without changing the conventional synthesis parameters. Therefore, this article highlights both the possibilities and limitations of GP catalyst synthesis.