Mn−Co Mixed Oxide Nanosheets Vertically Anchored on H₂Ti₃O₇ Nanowires: Full Exposure of Active Components Results in Significantly Enhanced Catalytic Performance

The full exposure of active ingredients plays an important role in the enhancement of catalytic performance. In this work, a series of novel catalysts, Mn−Co mixed oxide nanosheets with ultrathin thickness (about 3.5 nm) and different Mn/Co ratios (0.52, 0.69, and 1.52) vertically anchored on a support (H₂Ti₃O₇ nanowires), are rationally developed. This unique structure not only fully exposes the active ingredients of the Mn−Co mixed oxides, but also is very favorable for the diffusion and transfer of gas molecules through the space between these standing nanosheets. As expected, the developed catalysts (MnO_x-CoO_y/H₂Ti₃O₇, MnCoTi), especially MnCoTi-2 with the Mn/Co molar ratio of 0.69, present excellent low-temperature selective catalytic reduction (SCR) performance, high N₂ selectivity, superior water tolerance and stability. The relative turnover frequency (TOF) value over MnCoTi-2 at 100 °C is as high as 9.25×10⁻⁴ s⁻¹ under the gas hourly space velocity (GHSV) of 200 000 h⁻¹, which is rarely reported among Mn-Ti, Mn−Co, and Mn−Co-Ti mixed oxide catalysts. The results of in situ diffuse reflectance infrared Fourier transform spectroscopy suggest that the coordinated NH₃, NH₄ ⁺ ions, adsorbed NO₂, and bidentate nitrate are the reactive species and the Eley–Rideal and Langmuir–Hinshelwood mechanisms can be simultaneously involved on the surface of the MnCoTi-2 at a relatively low temperature (90 °C).