Cu-exchanged Al-rich OFF-CHA twin-crystal zeolite for the selective catalytic reduction of NOx by NH3.

The NOx conversion of Cu 3.1 -OFF-CHA-Fresh was maintained above 90 % in the range from 160 to 550 ℃, and it still remained above 80 % in the range 180–450 °C even after hydrothermal treatment. [Cu(OH)]+ was more affected by hydrothermal treatment than Cu2+ in Cu-OFF-CHA. Cu2+ in Cu-OFF-CHA was mainly migrated from CHA to OFF sites after hydrothermal treatment, and Cu2+ in OFF sites on Cu-OFF-CHA should be more stable, resulting in less conversion of Cu2+ to CuOx clusters. Thus, it is inferred that OFF zeolite was the main reason for excellent hydrothermal stability of Cu-OFF-CHA catalyst. [Display omitted] • Al-rich OFF-CHA zeolite twin-crystal was synthesized by one-pot hydrothermal method. • Cu-OFF-CHA exhibited excellent SCR activity and hydrothermal stability. • OFF zeolite was the main reason for excellent hydrothermal stability of Cu-OFF-CHA. Novel Al-rich OFF-CHA twin-crystal zeolite was synthesized by one-pot hydrothermal method, and applied in ammonia-selective catalytic reduction (NH 3 -SCR) after copper ion exchange. Results indicated that Cu content in Cu-OFF-CHA played a significant role in NH 3 -SCR reaction. The insufficiency of copper activity sites and the formation of CuOx were the main reasons affecting low and high temperature SCR activity of catalyst, respectively. Cu 3.1 -OFF-CHA, with the optimal copper content, demonstrated over 90 % NOx conversion and exhibited excellent N 2 selectivity in the range from 160 to 550 ℃. Further research verified that the SCR activity of Cu 3.1 -OFF-CHA maintained above 80 % in the temperature range from 180–450 °C after hydrothermal treatment 16 h. The reason might be that Cu2+ in Cu-OFF-CHA was migrated from CHA to OFF sites after hydrothermal treatment, and Cu2+ in OFF sites on Cu-OFF-CHA was more stable, resulting in less conversion of the active site to CuOx clusters. Cu-OFF-CHA has the potential to be applied in SCR after-treatment systems of diesel exhaust due to the excellent SCR activity and hydrothermal stability. [ABSTRACT FROM AUTHOR]