Decomposition of O3 onto natural Gobi dust: From uptake to surface reactivity

Abstract

International audienceBeyond synthetic metal oxides, this work investigates natural mineral dust as a material of interest for O3 uptake and decomposition. Ozone and Gobi dust interactions are addressed combining gas phase and adsorbed phase approach. It allows for determining: (i) the drivers of O3 decomposition process on Gobi and (ii) surface reactions and mechanism. First, the steady catalytic decomposition of ozone onto Gobi is explored on a large O3 concentration range: 20 ppb − 10 ppm, with steady uptake coefficients ranging from 2.6 x 10-9 to 6.2 x 10-8. If moisture (20 % RH) does not impact initial uptake of O3 it is evidenced to hinder the steady state behavior. Cyclic surface regeneration evidences that: (i) wet air flushing restores initial uptake properties, and (ii) mild thermal treatment (150 °C) restores the complete uptake process. Along O3 decomposition, adsorbed phase monitoring using DRIFT allows for identification and dynamic monitoring of specific IR bands on Gobi surface. Oxide and peroxide surface species are created. To meet environmental conditions, the role of water on surface groups created by O3 uptake is addressed through water molecule uptake experiments. Finally, a five-step mechanism is proposed to describe uptake and surface reactivity of O3 on Gobi dust. This work provides a comprehensive evaluation of the surface properties and reactivity of Gobi dust towards O3, valuable for atmospheric, geocatalytic and plasma-catalytic processes