Effects of K doping on Zn0.4Co2.6O4 spinel catalysts for low-temperature catalytic N2O decomposition in the presence of inhibitors

The recent development of NH₃ as a fuel has led to significant emissions of N₂O, a major greenhouse gas. Direct catalytic N₂O decomposition (de-N₂O) is a promising technology for N₂O emissions control because it effectively decomposes N₂O at low temperatures without requiring reducing agents or producing other pollutants. In marine applications, to improve the flame properties, NH₃ is often mixed with marine diesel oil, which contains sulfur. Although alkali-metal-doped Co-based catalysts show high de-N₂O activity at low temperatures, their performance in the presence of SO₂ has not been evaluated. In this study, we examined the effects of alkali metals on the Zn_0.4Co_2.6O₄ spinel-structured catalyst for low-temperature de-N₂O in the absence and presence of inhibitors (O₂, H₂O, and SO₂). Incorporating alkali metals (Na, K, Rb, and Cs) significantly enhanced the catalytic activity of the Zn_0.4Co_2.6O₄ spinel catalyst. Specifically, adding 1 wt% K reduced the light-off temperature from 271.7 °C to ∼150.0 °C at 60,000 h^-1 gas hourly space velocity in the absence of inhibitors. The enhanced electronic properties resulting from the addition of alkali metals led to weakening of Co-O bonds, promoting the regeneration of active sites and thus enhancing catalytic activity. K served as sacrificial sites for sulfur adsorption, delaying deactivation of the 1K-Zn_0.4Co_2.6O₄ spinel catalyst by SO₂. The formation of bulk sulfates, surface sulfites, and CoSO₄ was responsible for the deactivation by SO₂. Mechanisms for the deactivation by SO₂ and the promotion of SO₂ resistance by K in the Zn_0.4Co_2.6O₄ spinel catalyst are proposed.