Understanding the superior NH3-SCR activity of CHA zeolite synthesized via template-free interzeolite transformation

Abstract

Synthesizing CHA-type zeolite via template-free interzeolite transformation has been considered as a green method, but the resultant zeolite exhibits low activity in the selective catalytic reduction of NO_x by ammonia (NH₃-SCR). Herein we report a highly active NH₃-SCR catalyst (Cu-CHA_USY) derived from CHA-type zeolite (CHA_USY) that is synthesized via template-free interzeolite transformation from ultra-stable Y (USY). The ultra-high activity is attributed to the specific silicon and aluminum configurations in USY which are distinctly different from those in the conventionally used parent NaY, although they have similar SiO₂/Al₂O₃ ratios. This characteristic endows CHA_USY with more single Al atoms in a six-membered ring, benefiting the self-reduction of [Cu(OH)]⁺ and the activation of O₂ during the NH₃-SCR reaction. Moreover, Cu-CHA_USY is demonstrated to outperform the two reference catalysts prepared from the aluminosilicate gel by conventional hydrothermal crystallization with the assistance of organic templates. Our work provides a new strategy for preparing highly active NH₃-SCR catalysts.