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

Novel Al-rich OFF-CHA twin-crystal zeolite was synthesized by one-pot hydrothermal method, and applied in ammonia-selective catalytic reduction (NH3-SCR) after copper ion exchange. Results indicated that Cu content in Cu-OFF-CHA played a significant role in NH3-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. Cu3.1-OFF-CHA, with the optimal copper content, demonstrated over 90 % NOx conversion and exhibited excellent N2 selectivity in the range from 160 to 550 degrees C. Further research verified that the SCR activity of Cu3.1OFF-CHA maintained above 80 % in the temperature range from 180-450 degrees 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.