4 years ago

Experimental and Computational Interrogation of Fast SCR Mechanism and Active Sites on H-Form SSZ-13

Experimental and Computational Interrogation of Fast SCR Mechanism and Active Sites on H-Form SSZ-13
Sichi Li, Janos Szanyi, Feng Gao, Yang Zheng, William F. Schneider
Experiments and density functional theory (DFT) models are combined to develop a unified, quantitative model of the mechanism and kinetics of fast selective catalytic reduction (SCR) of NO/NO2 mixtures over H-SSZ-13 zeolite. Rates, rate orders, and apparent activation energies collected under differential conditions reveal two distinct kinetic regimes. First-principles thermodynamics simulations are used to determine the relative coverages of free Brønsted sites, chemisorbed NH4+, and physisorbed NH3 as a function of reaction conditions. First-principles metadynamics calculations show that all three sites can contribute to the rate-limiting N–N bond forming step in fast SCR. The results are used to parametrize a kinetic model that encompasses the full range of reaction conditions and recovers observed rate orders and apparent activation energies. Observed kinetic regimes are related to changes in most-abundant surface intermediates.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b01319

DOI: 10.1021/acscatal.7b01319

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