Insight into Low-Temperature Catalytic NO Reduction with NH3 on Ce-Doped Manganese Oxide Octahedral Molecular Sieves

Oxygen vacancy defect (OVD) as one of the crystal defects is critical to the reactivity of heterogeneous catalyst surface for catalytic NO reduction with NH3 (NH3-SCR). Here, we propose a simple and feasible method to enhance OVDs through Ce doping manganese oxide octahedral molecular sieves (Ce-K-OMS-2), where it was proven that Ce mainly enters the framework structure of K-OMS-2. The robust NH3-SCR catalytic test showed that the presence of Ce could lower the catalytic temperature and activity for NO conversion (similar to 100%) across a wide temperature span of 140-230 degrees C. The characterization results indicated the distortion of octahedral units after Ce substitution and the subsequent introduction of OVDs. Moreover, we demonstrated by density functional theory (DFT + U) calculations that the unique nanostructure of Ce doping K-OMS-2 with OVDs in the framework can alter the local bond lengths and the density of states, thereby obviously accelerating the low-temperature NH3-SCR. NH3 prefers to be adsorbed at the Ce site of Ce-K-OMS-2, while NO is much more likely to adsorb on the 0 site of Ce-K-OMS-2, following the Langmuir-Hinshelwood mechanism.