(691g) Impact of Field Aging on the Redox Half Cycles of NH3- Selective Catalytic Reduction of NOx over Commercial Cu-SSZ-13 Monolith Catalysts
AIChE Annual Meeting
2021
2021 Annual Meeting
Catalysis and Reaction Engineering Division
Environmental and Automotive Catalysis II: Pollutant Control
Tuesday, November 16, 2021 - 9:48am to 10:06am
Cu-SSZ-13 zeolites are commercial catalysts for NH3-selective catalytic reduction (SCR) of NOx present in diesel vehicle exhaust. Despite the commercial success, the associated reaction chemistry and mechanism are still not fully understood, which has made it difficult to assess the kinetic impact of field aging on the SCR reaction. A standard SCR reaction, 4NO+4NH3+O2â4N2+6H2O, consists of two redox halves: the reduction half cycle (RHC) and the oxidation half cycle (OHC) that cycle the Cu-inventory between +2 and +1 oxidation states. Most of the reported experimental and theoretical studies have been performed only in the NH3-solvation region (150°C-300°C). In the current work, we employ spatially resolved capillary inlet mass-spectrometry (SpaciMS) to investigate the SCR redox cycles at various spatial locations of commercial Cu-SSZ-13 monolith catalysts in their de-greened, hydrothermally aged, and field aged forms, in the temperature range of 200°C-450°C, thereby encompassing both the NH3 solvation region and high temperature region. A 10-step protocol was developed to measure RHC, OHC and SCR transients on the Cu-SSZ-13 samples with various initial Cu-oxidation state partitioning. With the help of kinetic modeling, these transients were then analyzed to understand the half-cycle kinetics, role of Cu-species and Bronsted acid sites. Moreover, NH3 temperature-programmed desorption experiments were performed to further elucidate the roles of Lewis- bound NH3 and Bronsted- bound NH3 in RHC and OHC. The SCR reaction was found to be OHC-limited in the NH3-solvation region, and RHC-limited in the high temperature region. While field aging slowed down both RHC and OHC, its impact on OHC was greater, which made the SCR reaction OHC-limited even in the NH3-solvated region. Understanding the impact of field aging on the SCR redox chemistry in both low and high temperature range will help in formulating SCR catalysts that will meet the rapidly increasing catalyst warranty and useful-life demand.