Cu-Exchanged CHA-Type Zeolite from Organic Template-Free Synthesis: An Effective Catalyst for NH₃‑SCR

A Cu-containing CHA-type zeolite was prepared via aqueous ion exchange of the CHA zeolite from organic template-free synthesis. The thus-obtained template-free Cu-CHA showed the best catalytic performance (i.e., high low- and high-temperature reactivity, wide temperature-window, and high hydrothermal stability) in ammonia selective catalytic reduction (NH₃-SCR) of NO_x among three investigated Cu-CHA zeolites. Different Cu ion distributions of these Cu-CHA catalysts were confirmed by deconvolution of NO adsorbed Fourier transform infrared spectra; the Cu-containing template-free CHA catalyst has a high amount of isolated Cu²⁺ in a six-membered ring (6MR). Furthermore, the framework Al distribution is investigated by ²⁹Si MAS NMR analysis, indicating that the catalyst has a high fraction of paired Al sites, which stabilize Cu²⁺ ions in the 6MR, leading to a high ability to resist the harsh hydrothermal aging.