PNNL

Abstract

The present contribution provides clarity to N2O formation mechanisms and key influencing factors during low temperature NH3-SCR, with the goal of enabling the rational design of advanced SCR catalysts with low greenhouse gas impact. By studying more than 50 small pore Cu-exchanged zeolite SCR catalyst samples, including model catalysts synthesized in our laboratories and state-of-the-art industrial catalysts, we explored a wide range of factors affecting N2O formation. These factors included Cu loading, support Si/Al ratio, support topology, catalyst aging, reaction temperature and reactant feed composition effects. We probed N2O formation under both steady-state SCR, and during NH4NO3 decomposition via temperature programmed desorption (TPD). Finally, we used DFT to probe energetics of possible N2O formation pathways. Based on these studies, we confirm that low temperature N2O formation occurs via multiple reaction pathways that all involve NH4NO3 and are supported by Cu moieties that facilitate in-situ NO oxidation to NO2.