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NH 3 adsorption and desorption behavior of a commercial Cu-chabazite (CHA) NH 3 selective catalytic reduction (NH 3-SCR) catalyst was studied in the presence and absence of H 2 O. NH 3 uptake values at various adsorption temperatures were obtained during various steps of the adsorption and temperature-programmed desorption (TPD) experiments. Total NH 3 uptake decreased from 4.6 to 1.6 g NH 3 /L catalyst when the adsorption temperature was increased from 50 to 300 • C. Three major adsorption sites for NH 3 adsorption could be identified and quantified using TPD experiments, namely loosely, moderately, and strongly bound NH 3 with peak centers at around 147, 266, and 447 • C. The total NH 3 uptake was significantly affected by the presence of H 2 O in the feed. This resulted in a significant uptake loss (nearly 60%) for the loosely bound NH 3. Three single-site and one three-site model were developed and compared in terms of NH 3 uptake and release. The effects of site density values and thermodynamic restrictions in one-site models were investigated. The model using site density values obtained during the TPD phase resulted in the best fit among one-site models. The three-site model, which uses site density values obtained using dry adsorption of NH 3 , best represented the experimental data.

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