Series of halogen engineered well-mixed oxides derived from layered double hydroxides for highly efficient NH3-SCR catalysts: Improvement of the oxygen vacancies

Reinforcing the development of efficient catalysts is crucial for addressing the challenges associated with NO_x removal technologies. Herein, we present a unique method for the in situ production of halogen-doped NiCoMoO_x catalysts utilizing a crystallization-thermal decomposition mechanism and the use of such catalysts for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). The formation of lattice defect (oxygen vacancies) and surface acid sites on Br-doped NiCoMoO_x catalyst was considerably enhanced compared with that on pure NiCoMoO_x, resulting in highly efficient reduction of NO_x and a broader temperature operating range. The 2Br-NiCoMoO_x catalyst achieved the highest NO_x conversion of 97.2 % at 250°C, while NiCoMoO_x was only 83 %, and the NO_x conversion was always above 80 % in a wide temperature window of 200 to 350 °C. Through comprehensive characterization, it was also revealed that the introduction of Br enhanced the low temperature redox performance and the adsorption and activation of NO and NH₃ on the catalyst surface, which played a crucial role in facilitating the reaction between NO and NH₃. Furthermore, we achieved broad temperature window NO_x reduction by ingeniously utilizing a tandem catalyst system composed of V₂O₅-WO₃/TiO₂ and 2Br-NiCoMoO_x, with the optimal mass ratio of the two phases being 1:3. This research presents novel design approaches that offer a new approach to the creation of high-performance SCR catalysts.