Ammonia Desorption Peaks Can Be Assigned to Different Copper Sites in Cu/SSZ-13

Artikel i vetenskaplig tidskrift, 2017

The purpose of this study is to attribute NH 3 -TPD peaks observed over Cu/SSZ-13 catalysts to different catalytic sites. This is done by comparing a large number of copper loadings, especially below 40% ion exchange, to be able to see effects relevant to sites in both 6-membered and 8-membered rings. We found that intermediate (200–300 °C) and high (400–500 °C) temperature NH 3 -TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H 2 -TPR and NO-DRIFTS. Thus we propose that these two TPD peaks represent ammonia stored on H and Cu sites in 6 and 8-membered rings, respectively. This assignment is further supported by the finding that the intermediate and high temperature NH 3 -TPD peaks of samples with different Si/Al ratios also follow the same trend. Moreover, we observe that the activation energy for ammonia oxidation is significantly lower for Cu in 6MR compared to Cu in 8MR rings. Graphical Abstract: [Figure not available: see fulltext.].