Graphene Oxide-Promoted Mn–Ce Oxide Catalysts for Superior Low-Temperature NH3–SCR of NO x

Abstract

Low-temperature NH3–SCR requires catalysts that are simultaneously highly active and highly N2-selective below 200 °C, a combination difficult to achieve with Mn–Ce oxides (MnCeOx) because the strong oxidizing character needed to activate NO also promotes NH3 overoxidation. Here, graphene oxide (GO) was incorporated into MnCeOx by a mild room-temperature rheological-phase route without calcination. GO enlarges the specific surface area from 93.1 to 167.2 m2 g–1, confines the Mn–Ce oxides into highly dispersed low-crystallinity nanoparticles, and redistributes the surface valence states, raising the Mn4+ fraction from 24.8% to 36.9%, the Ce3+ fraction from 15.3% to 24.6%, and chemisorbed oxygen (Oβ) from 36.4% to 57.9%. The optimal MCGO(2) reaches >90% NOx conversion and >80% N2 selectivity at 100–200 °C (GHSV 80,000 mL gcat–1 h–1), with a relative turnover frequency per Mn atom 3.1 times that of GO-free MnCeOx. Normalizing the rate by surface area and Mn atoms shows that the promotion arises mainly from the enlarged surface area and improved dispersion, with an additional intrinsic contribution from the modified surface redox chemistry. In situ DRIFTS confirms that GO strengthens NH3 adsorption, suppresses its overoxidation, and enables the Langmuir–Hinshelwood pathway. MCGO(2) also shows good stability and reversible H2O deactivation.