Efficient Experimental Approach to Evaluate Mass Transfer Limitations for Monolithic DOCs

Abstract

The diesel oxidation catalyst (DOC, Pt/γ-Al 2 O 3 ) was used in a synthetic-gas catalyst test bench to study internal mass transfer limitations during NO oxidation. A simple and fast experimental methodology, by varying the washcoat thickness in monolithic DOCs was developed and the results were evaluated using various experimental time scales. The ratio between the reaction time constant and the washcoat diffusion time constant was useful in identifying temperatures where the DOCs tested transitioned between a kinetically controlled region and an internal mass transfer controlled region. The NO conversion was shown to be significantly limited by internal mass transfer already at 175 °C for an average washcoat thickness of 110 µm.