Kinetic model comparison and elucidation of mass transfer limitations in NH3-SCR reactors using Vanadia based washcoats with different thicknesses

Kinetic models of NH3-SCR of NO based on modified redox (MR) and modified Eley-Rideal (ER) mechanisms calibrated using monoliths with Vanadia based washcoats with different thicknesses were cross compared. Both models were satisfactory for the washcoat thicknesses investigated at steady conditions in 120-540 degrees C range. MR mechanism better represented NO transients at 192 degrees C. Dependence of limiting regions on the washcoat thickness was determined via the analysis of washcoat concentration profiles and the concentration ratios of the fluid, fluid-washcoat interface and washcoat. Both models generally agreed with the borders of the limiting regions. During Standard SCR, the limits of the kinetic regime was below 309 and 271 degrees C for thinner and thicker washcoats, respectively. This was followed by mixed limitation regime upto 488 degrees C at the reactor entrance. Above 488 degrees C, transition to kinetically controlled regime was observed at the center of the monolithic reactors. (C) 2021 Elsevier Ltd. All rights reserved.