Revealing the crystal-plane effects of CuO during the NH₃-SCR over CuO/TiO₂ catalysts

Copper-based (Cu-based) catalysts have garnered significant attention for their potential in ammonia-selective catalytic reduction (NH₃-SCR) of nitrogen oxides (NO_x). However, the widespread industrial application of Cu cation-exchanged chabazite catalysts has been hindered by poor hydrothermal stability, expensive raw materials, and complicated preparation. As a result, copper oxide-based (CuO-based) catalysts have emerged as ideal candidates due to their low cost and facile preparation. Nevertheless, the performance of NH₃-SCR catalysts is a significantly influenced by the crystal plane effect, which has been scarcely investigated in Cu oxide-based NH₃-SCR catalysts. In this study, CuO with exposed {001} and {111} facets were synthesized and combined with titanium dioxide (TiO₂) support to construct CuO/TiO₂ composite NH₃-SCR catalysts. These catalysts displayed divergent NO_x removal performance due to the crystal-plane effects of CuO. Specifically, the proportion of Cu⁺ and surface-adsorbed oxygen (O_α) in CuO(111)/TiO₂ catalyst was higher than that of CuO(001)/TiO₂ catalyst, which could facilitate the NH₃-SCR reactions. The NH₃-TPD, NO-TPD, and DFT calculations demonstrated the better NH₃ and NO adsorption capability of CuO(111)/TiO₂ catalyst than that of CuO(001)/TiO₂ catalyst. Furthermore, the more -NH₂ and nitrate species in CuO(111)/TiO₂ catalyst resulted in better NO_x removal efficiency than CuO(001)/TiO₂ catalyst. This study provides fundamental insights on the crystal-plane effect of CuO, which is critical for optimizing Cu oxide-based NH₃-SCR catalysts.