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.
Four commercial monolithic diesel oxidation catalysts (DOCs) with two different platinum group metal (PGM) loadings and Pt:Pd ratios of 1:0, 2:1, 3:1 (w/w) were investigated systematically for CO, C 3 H 6 , and NO oxidation, CO-C 3 H 6 co-oxidation, and CO-C 3 H 6 -NO oxidation reactions via transient activity measurements in a simulated diesel engine exhaust environment. As PGM loading increased, light-off curves shifted to lower temperatures for individual and co-oxidation reactions of CO and C 3 H 6 . CO and C 3 H 6 were observed to inhibit theoxidation of themselves and each other. Addition of Pd to Pt was found to enhance CO and C 3 H 6 oxidation performance of the catalysts while the presence and amount of Pd was found to increase the extent of self-inhibition of NO oxidation. NO inhibited CO and C 3 H 6 oxidation reactions while NO oxidation performance was enhanced in the presence of CO and C 3 H 6 probably due to the occurrence of reduced Pt and Pd sites during CO and C 3 H 6 oxidations. The optimum Pt:Pd ratio for individual and co-oxidations of CO, C 3 H 6 , and NO was found to be Pt:Pd = 3:1 (w/w) in the range of experimental conditions investigated in this study.
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