Impact of diffusion limitations inside the wall of catalytic filters on conversion of gaseous pollutants at increased flow rates

Abstract

In this paper we present a methodology for experimental observation of mass-transfer limitations in catalytic filter wall and their impact on the outlet conversion of gaseous pollutants. Series of cordierite filter samples are coated in the lab with a model Pt/γ-Al2O3 catalyst to obtain different structures that are characterized by cross-section SEM images. Pressure drop and CO oxidation experiments are performed, focusing on the performance at higher flow rates. The presence of permanent CO slip above the light-off temperature provides a clear evidence of diffusion limitations in wall pores. While all the samples including the filter with an uncoated zone exhibit negligible CO slip at lower flow rates, there are significant differences at higher flow rates (space velocity 100000 h−1 and above). Thanks to more uniform catalyst distribution inside the wall pores, the filters coated with the suspension d90 = 0.3 µm exhibit a lower CO slip than the filters coated with d90 = 4 µm.