(375e) First Principles Simulation of NO Oxidation on Cu-SSZ-13 Zeolite Catalyst

Nitrogen Oxides (NO_x) are pollutants generated in oxygen rich combustion. In an increasingly more stringent emission regulations, ammonia Selective Catalytic Reduction (NH₃-SCR) of NO_x into N₂ and H₂O is the leading technology in diesel and stationary sources. However, the active sites and reaction mechanism of the commercially used Cu-exchanged zeolite SCR catalyst, i.e. Cu-SSZ-13, are still being investigated. 

Past research has shown that the presence of NO₂ affects NH₃-SCR reaction mechanism and activity. Hence, we began our study by modeling the NO oxidation reaction on Cu-SSZ-13 using first-principles calculations to model two different active sites: single and dimeric Cu.

We examine the preferred locations of single and dimeric Cu species within the confines of SSZ-13 microporous structure in a periodic supercell. On these two sites, we compute GGA and hybrid adsorption energy of relevant intermediates (O, O₂, NO, NO₂, NO₃) involved in NO oxidation. We explore co-adsorption of these intermediates in the two active sites to probe Cu-SSZ-13 capability of accommodating more than one adsorbate. We then employ the use of thermodynamic phase diagram under NO oxidation condition to examine the most stable species. Comparing the computed NO oxidation pathway under reaction conditions on both sites, we conclude that Cu dimer provides a more accessible pathways, consistent with experimental observations.