The Mechanism of N2O Decomposition on Co3O4-Based Catalysts: Effects of Support on Reactivity

Yongchun  Hong, UC Berkeley

Nitrous oxide (N₂O) causes atmospheric changes as an ozone-depleting reagent and as a substance with global warming potential about 300-fold greater than CO₂. N₂O forms as a potential side product in exhaust treatment strategies based on selective catalytic reduction of NO_x. The catalytic decomposition of N₂O to O₂ and N₂ is favored by thermodynamics; it represents a practical and effective remediation strategy, but currently available catalytic materials show insufficient reactivity, especially in O₂-rich streams, because of strong inhibition by the residual O₂ present in diesel exhaust. Here, we examine mechanistic details of N₂O decomposition routes and the origins of such inhibition effects on Co₃O₄ domains, both as bulk powders and as dispersed active structures. We show that N₂O decomposition on Co₃O₄ is inhibited by O* formed via quasi-equilibrated O₂ chemisorption; the kinetically-relevant step involves N-O cleavage step via interactions between N₂O species bound at an O-vacancy and a vicinal lattice O-atom (N₂O* + O* = N₂ + O₂ +2*) at stoichiometric Co₃O₄ surfaces. As a result, turnover rates increase as the number of binding sites (*) increases, a reflection of the reduction properties of Co³⁺ cations in these oxide domains, with larger domains and semiconducting supports leading to more reducible cations.