Experimental and theoretical study of NH3 adsorption and desorption over a Cu-chabazite NH3 -SCR catalyst

Abstract

NH3 adsorption and desorption behavior of a commercial Cu-chabazite (CHA) NH3 selective catalyticreduction (NH3 -SCR) catalyst was studied in the presence and absence of H2 O. NH3 uptake values at various adsorptiontemperatures were obtained during various steps of the adsorption and temperature-programmed desorption (TPD)experiments. Total NH3 uptake decreased from 4.6 to 1.6 g NH3 /L catalyst when the adsorption temperature wasincreased from 50 to 300 ◦ C. Three major adsorption sites for NH3 adsorption could be identified and quantified usingTPD experiments, namely loosely, moderately, and strongly bound NH3 with peak centers at around 147, 266, and 447◦ C. The total NH3 uptake was significantly affected by the presence of H2 O in the feed. This resulted in a significantuptake loss (nearly 60%) for the loosely bound NH3 . Three single-site and one three-site model were developed andcompared in terms of NH3 uptake and release. The effects of site density values and thermodynamic restrictions inone-site models were investigated. The model using site density values obtained during the TPD phase resulted in thebest fit among one-site models. The three-site model, which uses site density values obtained using dry adsorption ofNH3 , best represented the experimental data.