Abstract
The purpose of this study is to attribute NH3-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 NH3-TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H2-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 NH3-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
Highlights
IntroductionElectronic supplementary material The online version of this article (doi:10.1007/s10562-017-2083-8) contains supplementary material, which is available to authorized users
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.In the current framework of increasingly stringent N Ox emission regulations, the continuous improvement of N Ox removal technologies is critical
The overall similarity in the ratio S1/S2 obtained from both DRIFT and NH3 storage, which is clearly seen in Fig. 5c, further supports our proposal that the TPD peaks at intermediate and high temperature can be assigned to ammonia storage in 6-membered rings (6MR) and 8MR units, respectively
Summary
Electronic supplementary material The online version of this article (doi:10.1007/s10562-017-2083-8) contains supplementary material, which is available to authorized users. While there are two published studies using different copper loadings as a tool to understand the TPD peaks [2, 3, 7], neither correlated ammonia storage with different positions in the zeolite. The goal of this study is to use a large number of Cu/SSZ-13 samples with loadings above and below 20% IE to interpret the ammonia-TPD peaks and correlate them with sites in different locations in the zeolite. Another factor that we take into consideration to make the assignment of the TPD peaks easier, is the presence of CuO species. In addition we aim to assign DRIFT peaks to the different sites and use Cu/SSZ13 samples with different Si/Al ratios to further support the assignment of Cu sites to specific positions
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