One-Pot Synthesis of the Cu-SAPO-18 Catalyst Using Waste Mother Liquid and its Application in the SCR of NO_x with NH₃

Abstract

A green and efficient way of synthesizing Cu-SAPO-18 was developed, which is characterized by the one-pot method and recycling of the mother liquid. All fresh samples synthesized with or without the mother liquid exhibit similar structural properties, Si/(P + Al), and particle sizes. However, all fresh catalysts show some differences in Brunauer−Emmett−Teller surface areas, Cu content, roughness of the crystal surface, and Si coordination. Temperature-programed desorption of ammonia, 29 Si magic angle spinning nuclear magnetic resonance, temperature-programmed reduction experiments by H 2 , electron paramagnetic resonance, and UV−vis-diffuse reflectance spectroscopy results suggest that the mother liquid declines the content of acid sites, Cu 2+ and CuO of Cu-18-0.5 and Cu-18-1. Therefore, Cu-18-0.5 and Cu-18-1 exhibit a decline in low-temperature activity but an increase in high-temperature activity, compared to Cu-18-0. During aging treatment, the mother liquid contributes to the movement of CuO to ion-exchange sites and new isolated Cu 2+ ions are generated. However, excess mother liquid causes severe structural damage of Cu-18-1. Finally, Cu-18-0.5 exhibits the best hydrothermal stability owing to the more active Cu 2+ sites and less structural collapse.