Cu/SAPO-34 prepared by a facile ball milling method for enhanced catalytic performance in the selective catalytic reduction of NOx with NH3

Abstract

Cu/SAPO-34 catalysts were prepared by different solid-state ion exchange methods, i.e., mechanical mixing (Cu/SAPO-34-M) and ball milling (Cu/SAPO-34-B), and were used for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) reaction. Compared with Cu/SAPO-34-M, Cu/SAPO-34-B exhibited more excellent NH₃-SCR catalytic activity. Various characterization methods, including XRD, SEM, N₂ adsorption–desorption, UV-vis, H₂-TPR, EPR, NO + O₂-TPD, NH₃-TPD, and in situ DRIFTS, were used to elucidate their different catalytic performances. The characterization results suggested that ball milling could be beneficial for increasing the amount of isolated Cu²⁺ ions in the Cu/SAPO-34 catalyst. In comparison with Cu/SAPO-34-M, Cu/SAPO-34-B had more isolated Cu²⁺ ions, which mainly contributed to the NO_x adsorption and Lewis acid sites. Furthermore, ball milling could improve the redox property of the Cu/SAPO-34 catalyst. The in situ DRIFTS results verified that NH₃ adsorbed on Lewis acid sites were more active than those adsorbed on Brønsted acid sites. Therefore, it was believed that ball milling was a suitable method to prepare more efficient Cu/SAPO-34 catalysts for NO_x removal from diesel exhaust.