Sulfur poisoning of Cu-SSZ-13 for NH3-SCR: kinetic model development

Yasser  Jangjou, University of Virginia

Sulfur poisoning of Cu-SSZ-13 for NH3-SCR: kinetic model development


Yasser Jangjou1, Di Wang2 Ashok Kumar2 Junhui Li2, William S. Epling*1

1) Department of Chemical Engineering, University of Virginia, Charlottesville, VA 22904 (USA)

2) Cummins Inc., Catalyst Technology, Columbus, Indiana 47201 (USA)

*, Tel.: +1 (434) 924-6278


Cu-SSZ-13, an ion-exchanged small pore zeolite with a chabazite structure, reportedly has superior activity and stability for NH3-SCR applications compared to other candidates such as medium or large pore zeolites [1]. However, under practical conditions, sulfur poisoning inhibits low temperature (< 350 °C) SCR activity over Cu-SSZ-13 [2]. Despite these previous studies focused on sulfur poisoning, there are remaining questions as the S poisoning mechanism is yet to be fully understood. Here, an attempt was made to first experimentally study the sulfur poisoning mechanism with regards to the two main Cu active centers, i.e. Z2Cu and ZCuOH, available in Cu-SSZ-13. Then, a detailed NH3-SCR kinetic model capable of describing the behaviour of fresh, sulfated and regenerated catalysts was developed.

Two model Cu-SSZ-13 catalysts with different Si/Al ratios were prepared using a recipe reported by Gao et al. [3]. To characterize the prepared samples and quantify amount of Cutot and Z2Cu and ZCuOH, inductively coupled plasma optical emission spectroscopy (ICP-OES), H2 temperature programmed reduction (H2-TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used. Temperature programmed desorption (TPD) and in-situ DRIFTS experiments were performed to study adsorption and desorption dynamics of S species on different active sites. A micro-reactor setup (described elsewhere [4]) was used to carry out NH3-SCR activity tests over fresh, sulfated and de-sulfated samples. The results show that the responses of Z2Cu and ZCuOH to sulfur poisoning differ. More specifically, the nature of the S intermediates as well as the poisoning mechanism are site specific. It was found that S, depending on which site it is being adsorbed on, can either be present as ammonium sulfate (decomposes at ~380 °C) or copper bisulfite (decomposes at ~580 °C) resulting in different poisoning and deSOx routes on Z2Cu versus ZCuOH.

To develop the kinetic model, GT-ISE v2017 software was used to define the reaction scheme and solve the governing equations for gas-phase and surface concentrations and temperatures. The mechanism input included NH3 adsorption and desorption, SCR, ammonium sulfate formation and decomposition, and Cu bisulfite formation and decomposition. Taking into account this unique behaviour, kinetic parameters were optimized to minimize the error between the experimental data and model prediction. The developed kinetic model accurately predicts the experimental behaviour of the catalyst observed in our micro-reactor setup.



[1] A. M. Beale, F. Gao, I. Lezcano-Gonzalez, C. H. F. Peden, and J. Szanyic, “Recent advances in automotive catalysis for NOx emission control by small-pore microporous materials,” Chem. Soc. Rev. 44, 7371 (2015).

[2] L. Zhang, D. Wang, Y. Liu, K. Kamasamudram, J. Li, and W. S. Epling, “SO2 poisoning impact on the NH3-SCR reaction over a commercial Cu-SAPO-34 SCR catalyst,” Appl. Catal. B: Environmental 156, 371 (2014).

[3] F. Gao, N. W. Washton, Y. Wang, M. Kollár, J. Szanyi, and C. H. F. Peden, “Effects of Si/Al ratio on Cu/SSZ-13 NH3-SCR catalysts: Implications for the active Cu species and the roles of Brønsted acidity.” J. Catal. 331, 25 (2015).

[4] Y. Jangjou, D. Wang, A. Kumar, J. Li, and W. S. Epling, “SO2 Poisoning of the NH3-SCR Reaction over Cu-SAPO-34: Effect of Ammonium Sulfate versus Other S-Containing Species,” ACS Catal. 6, 6612 (2016).


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