Experimental and theoretical study of NH$_{3}$ adsorption and desorption over a Cu-chabazite NH$_{3}$-SCR catalyst

Abstract

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 $^{\circ}$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 $^{\circ}$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.