Inter-particle migration of Cu ions in physically mixed Cu-SSZ-13 and H-SSZ-13 treated by hydrothermal aging

Physically mixed Cu-SSZ-13 and H-SSZ-13 catalysts were prepared using two different methods to control the extent of contact between the particles; one was mixed by grinding the particles that were supposed to be in close contact (PM-C) with a mortar, and the other was a mixture of granules that were in loose contact (PM-L). After hydrothermal treatment at 550 °C for 4 hours, we observed that the two physically mixed catalysts had different distributions of copper (Cu) species and catalytic activities although the Cu loadings were the same. The characteristics of the Cu species were investigated by H2-TPR, NH3-TPD, DRIFT and EPR analysis. The catalytic activities were evaluated by the NH3-SCR reaction. The differences in the distribution of Cu species are attributed to the migration of Cu ions via direct contact between particles in PM-C because they prefer to be located at more energetically stable sites, which in this study is referred to as ‘inter-particle migration’. This research reports the migration of copper ions over much longer distances than previously reported that is regarded as an important factor for deactivation due to hydrothermal aging.