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 Zn0.4Co2.6O4 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 Zn0.4Co2.6O4 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-Zn0.4Co2.6O4 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 Zn0.4Co2.6O4 spinel catalyst are proposed.