Enhanced low-temperature performance of Al-rich Cu-SSZ-13 by Ce modification upon hydrothermal aging for NH3-SCR

Abstract

3wt.% Cu/SSZ-13 (Cu3/Z) and Ce modified 3wt.% Cu/SSZ-13 (Ce-Cu3/Z) catalysts were prepared and then hydrothermally aged. The Ce-modified Ce-Cu3/Z catalyst revealed excellent NH3-SCR activity and hydrothermal stability. Combined with a series of characterizations, it was proved that the introduction of Ce could inhibit the dealumination, and prevent the aggregation of Cu ions to form CuOx and CuAl2O4 species upon hydrothermal aging, thus improving the hydrothermal stability of Ce-Cu3/Z. In addition, Ce could interact with Cu species to enhance the reducibility of catalyst, and the interaction between Ce and Cu species was strengthened after hydrothermal aging. Also, the presence of Ce species could enhance the NH3 and NOx adsorption capacity of the catalyst, resulting in higher NH3-SCR activity of Ce-Cu3/Z after hydrothermaly aged at 700 °C. In situ DRIFTS results showed that the NH3-SCR reaction followed both E-R and L-H mechanisms on the Cu3/Z-700 and Ce-Cu3/Z-700 catalysts at 150 °C. Ce doping could promote the formation of L-NH3 (NH3 species coordinated to Lewis acid sites) and nitrate species on the Ce-Cu3/Z-700 catalyst, as well as the involvement of L-NH3 in the reaction, which play a crucial role as the main active intermediates at low temperature.