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

Abstract

Copper-based (Cu-based) catalysts have garnered significant attention for their potential in ammonia-selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx). 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 NOx removal performance due to the crystal-plane effects of CuO. Specifically, the proportion of Cu+ and surface-adsorbed oxygen (Oα) 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 NOx 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.