Water-Driven Surface Lattice Oxygen Activation in MnO2 for Promoted Low-Temperature NH3–SCR

Water is ubiquitous in various heterogeneous catalytic reactions, where it can be easily adsorbed, chemically dissociated, and diffused on catalyst surfaces, inevitably influencing the catalytic process. However, the specific role of water in these reactions remains unclear. In this study, we innovatively propose that H2O-driven surface lattice oxygen activation in γ-MnO2 significantly enhances low-temperature NH3–SCR. The proton from water dissociation activates the surface lattice oxygen in γ-MnO2, giving rise to a doubling of catalytic activity (achieving 90% NO conversion at 100 °C) and remarkable stability. Comprehensive in situ characterizations and calculations reveal that spontaneous proton diffusion to the surface lattice oxygen reduces the orbital overlap between the protonated oxygen atom and its neighboring Mn atom. Consequently, the Mn–O bond is weakened and the surface lattice oxygen is effectively activated to provide excess oxygen vacancies available for converting O2 into O2–. Therefore, the redox property of Mn–H is improved, leading to enhanced NH3 oxidation-dehydrogenation and NO oxidation processes, which are crucial for low-temperature NH3–SCR. This work provides a deeper understanding and fresh perspectives on the water promotion mechanism in low-temperature NOx elimination.