Effects of post-treatment method and Na co-cation on the hydrothermal stability of Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx with NH3

摘要

Post-treatment with dilute HNO3 solution after one-pot synthesis was an effective method to prepare excellent Cu-SSZ-13 catalysts for the selective catalytic reduction of NOx with NH3 (NH3-SCR). Using solutions with varying levels of acidity, catalysts with different Cu and Na contents were obtained, and the Cu3.9Na0.8-SSZ-13 catalyst showed the optimal NH3-SCR activity and hydrothermal stability. As co-cations, Na+ ions affected the hydrothermal stability of the one-pot-synthesized Cu-SSZ-13 catalysts greatly. Poorer hydrothermal stability was observed for catalysts with higher Na+ contents. The results of Al-27 and Si-29 NMR spectra proved that Na+ ions did not influence the Si(nAl) distributions in the catalysts significantly. However, H-2-TPR profiles indicated that excess Na+ ions in the catalysts decreased the stability of Cu species seriously. Thus, poor stability of Cu species caused by excess Na+ ions was the direct reason for the poor hydrothermal stability of the catalysts. Because of the negative effect on hydrothermal stability, excess Na+ ions should be avoided in Cu-SSZ-13 catalysts prepared by the one-pot synthesis method. (C) 2015 Elsevier B.V. All rights reserved.