Catalytic oxidation in wall-flow reactors with zoned coating

Modern diesel engine technology has recently adopted the wall-flow particulate filter technology. Most commercial filters are also catalyst coated, which gives the potential option to combine oxidation and filtration functionalities in a single reactor. Due to high precious metal costs, it is desirable to make optimal usage of the catalytic coating by applying catalyst zoning. The present study presents and applies a mathematical model that is able to describe the governing heat, mass transfer and chemical reaction phenomena occurring in a wall-flow monolithic reactor with axially variable catalytic activity. The results show that a zoning scheme with more catalysts in the frontal part is beneficial for CO and HC conversion in cold-start transients. The trends are inversed in the case of a simulated cool-down scenario. The effect of different zoning schemes is investigated in a fully transient legislated driving cycle corresponding to a passenger car application. The reactors’ performances are analyzed by examining the transient temperature and species profiles in the inlet and outlet channels. It was shown that the conversion efficiency is a complex function of combined thermal, species transport and reaction phenomena. The results highlight the increased engineering flexibility provided by the catalyst zoning technology and the challenges faced in applications where transient operating conditions prevail.