Dizel motorlu ağır iş makinelerinin motor sonrası sistemi kalibrasyonu için ticari bir katalizör kullanılarak NOX'un amonyak ile seçici katalitik indirgenmesinin üç-siteli kinetik modeli

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia is an efficient process for NOx abatement in diesel powered heavy duty vehicles. In the first part of this study, mass transfer limitations for standard SCR reaction in a monolith reactor over a commercial copper-chabazite (Cu-CHA) washcoated catalyst were investigated using a single reaction model. Results revealed that the intrinsic kinetic parameters obtained at low temperatures cannot account for SCR activity at higher temperatures and external mass transfer limitations exist at temperatures above 350 °C. Accordingly, in the second part, a multi-site kinetic model, in combination with internal and external mass transfer effects, was developed for ammonia SCR of NOx over CuCHA. NH3 adsorption & desorption, NH3 oxidation, NO oxidation and standard SCR reactions as well as the N2O formation reactions were studied separately in the temperature range of 100 to 600 °C using a monolith reactor. NH3 adsorption and desorption profiles showed good agreement with a kinetic model based on three different sites for ammonia storage on Cu-CHA. These three sites are believed to be monocopper species located near/on 6-membered ring of the chabazite structure, copper oxide clusters or coppers which move to the large cages at high temperatures and sites on which ammonia binds loosely. Site densities and coefficients of the mass transfer coefficient correlation for square channeled cordierite honeycomb monoliths, (𝑆ℎ = 𝐴(1 +𝐵(𝑅𝑒)(𝑆𝑐)(𝑑ℎ/𝐿))𝐶), were regressed from NH3 adsorption breakthrough and temperature programmed desorption data. The activation energies and pre-exponential factors for NH3 adsorption & desorption, NH3 oxidation, NO oxidation, standard SCR, and N2O formation reactions were also regressed from experimental data. The three site kinetic model is in excellent agreement with the experimental data at a wide temperature range (100 to 600 °C). The model also predicted very well standard SCR reactor effluent composition at different flow rates, which were not considered during the parameter estimation. Findings of this study revealed that correlations in the literature for estimation of mass transfer coefficients in monolith reactors were not appropriate for these systems (NH3-SCR). Therefore, mass transfer coefficients should be regressed from experimental data at conditions of interest for accurate prediction of SCR activity.