Fundamental insights into the active sites and kinetics of ammonia oxidation over Cu/SSZ-13 catalysts

Yiqing  Wu, Pacific Northwest National Laboratory

Fundamental insights into the active sites and kinetics of ammonia oxidation over Cu/SSZ-13 catalysts 

Yiqing Wu, Kenneth G. Rappé, Yong Wang, Feng Gao

Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99354, USA

*Corresponding author: feng.gao@pnnl.gov

Abstract:

The commercialization of selective catalytic reduction of NOx with NH3 has achieved great successes in recent years1. In order to achieve the desired NOx conversions, excess quantities of urea are typically introduced to the SCR systems, which leads to the release of unreacted NH3, called NH3 slip. To address this issue, the ammonia selective oxidation (NH3-SCO) process has been developed to oxidize the unreacted NH3 to nitrogen and water vapor. Cu-exchanged small-pore SSZ-13 zeolite catalysts (Cu/SSZ-13) have shown promising performance in the NH3-SCO, yet the nature of active sites and mechanistic interpretations have remained elusive2.

In this work, 3%Cu/SSZ-13 with zeolite Si/Al ratios ranging from 6 to 36 were prepared as model catalysts in order to achieve well-defined, but varied distributions of different Cu sites, including Cu2+-2Z, [Cu2+OH]+-Z and CuOx clusters3. In the present study, the correlation between the distribution of these active sites and the Si/Al ratios of SSZ-13 zeolite were established, allowing us to identify and distinguish the contribution from each type of active sites. Hydrothermal stability is of great importance to the performance and lifetime of Cu/SSZ-13 catalysts, and thus, were examined via hydrothermal aging at 650 °C for 100 hours. Kinetic studies were carried out to gain fundamental insights into the active sites and reaction mechanisms of Cu/SSZ-13 catalysts in NH3-SCO. The effects of feed composition, such as the NH3 and O2, on the activity and selectivity were also studied in this work.

References:

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[2]. Zhang, T.; Chang, H.; You, Y.; Shi, C.; Li, J., Environmental Science & Technology 2018, 52 (8), 4802-4808.

[3]. Paolucci, C.; Parekh, A. A.; Khurana, I.; Di Iorio, J. R.; Li, H.; Caballero, J. D. A.; Shih, A. J.; Anggara, T.; Delgass, W. N.; Miller, J. T.; Ribeiro, F. H.; Gounder, R.; Schneider, W. F., J Am Chem Soc 2016, 138 (18), 6028-6048.