Transition metal exchanged zeolites are among very promising catalysts for various applications. Their activity stems from single transition metal atoms located at well- defined extra-framework positions and is controlled by their precise chemical environment, which is highly dependent on the positioning of Al atoms in the framework. In this work we characterize the distribution of the Al atoms in the zeolite with the smallest unit cell size, SSZ-13 and show how it can be used to identify the active sites in the selective catalytic reduction of NOx in the presence of NH3. In a first step we identify all possibilities to distribute Al atoms in the unit cell and model finite temperature infrared spectra of CO adsorbed to Cu(I)-exchanged SSZ-13. Based upon ab-initio molecular dynamics simulations we are able to assign a two peak spectrum to the most stable site and we find excellent agreement with experimental measurements at low ion exchange levels. In a second step we compare finite temperature spectra of NO adsorbed to Cu(II) sites in the material. Energetic and combinatorial considerations then allow connecting the distribution of Cu-sites to the distribution of Al atoms in the framework. We subsequently use the Al-distribution to predict a Cu(II)-site distribution in the material, which when compared to experiment allows the clear identification of the active site in this material. In conclusion, we demonstrate that by identifying the positioning of the Al atoms in the framework and using ab-initio DFT calculations we are able to predict a distribution of any TM sites inside the framework and thus understand/predict the chemical activity of the material.

Decoding the zeolite genome and its application in understanding the active sites in the selective catalytic reduction of NOx using NH3 in Cu-SSZ13

249th National Meeting (2015)

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