Unexpected increase in low-temperature NH3-SCR catalytic activity over Cu-SSZ-39 after hydrothermal aging

Abstract

The control of nitrogen oxides (NOx) from heavy-duty diesel vehicles is becoming increasingly urgent due to its detrimental effects on the environment. Cu-SSZ-39, with its exceptional NH3-SCR activity and hydrothermal stability, has attracted more and more attention in the field of diesel vehicle emission control. In this work, an unexpected phenomenon was observed for Cu-SSZ-39 after hydrothermal aging. Generally, the hydrothermal aging process causes deterioration of the catalytic performance of catalysts. However, a remarkable increase in low-temperature NH3-SCR catalytic activity was observed in Cu-SSZ-39 after it was exposed to 850 ℃ hydrothermal aging conditions for 16 h. EPR, DRIFTS, H2-TPR, UV–vis and XANES were utilized to detect the changes in Cu species. It was determined that a portion of the Cu2+ ions near double six-membered rings (d6r) transformed into CuxOy species after hydrothermal treatment. These CuxOy species facilitated the production of nitrate species which were critical intermediates in the NH3-SCR process, resulting in an increase in low-temperature catalytic activity.