Unifying redox kinetics for standard and fast NH₃-SCR over a V₂O₅-WO₃/TiO₂ catalyst

A dynamic Mars-van Krevelen kinetic model that unifies Standard and Fast SCR reactions into a single redox approach is herein proposed for V-based catalysts for NOx removal from Diesel exhausts. Such a mechanistic model is consistent with the detailed catalytic chemistry proposed for the NH₃-NO/NO₂ reacting system in which NO₂ disproportionates to form nitrites and nitrates, nitrates are reduced by NO to nitrites in a key redox step, and nitrites react with NH₃ to form N₂ via decomposition of unstable ammonium nitrite. Intrinsic kinetic parameters were estimated by global multiresponse nonlinear regression of 42 transient runs. The model accounts for stoichiometry, selectivity, and kinetics of the global SCR process, reproducing successfully both the steady-state and transient behaviors of the SCR reacting system over the full range (0-1) of NO₂/NOx feed ratios in the 175-425°C temperature range. © 2009 American Institute of Chemical Engineers AIChE J, 2009