Ceramic foams as structured catalyst inserts in gas–particle filters for gas reactions—Effect of backmixing

Ceramic open cell foams have recently been proposed as a new catalyst structure to benefit from its characteristic properties like low pressure drop at relatively high specific surface and enhancement of heat and mass transfer. This study focuses on the application of an impregnated ceramic foam inside a gas–particle filter element to create a multifunctional reactor configuration. Selective catalytic NO reduction (SCR) and C3H6 oxidation over a V2O5–WO3–TiO2 catalyst are used as model reactions. Experiments were performed in two different reactor configurations (axial flow in cylindrical foam, radial flow in foam ring) and at typical conditions of filtration in flue gas cleaning (low gas velocity, low concentrations) and compared with data from a particle fixed bed as reference structure. Experiments at various temperatures (150–340 °C) and modified residence times (0.02–0.07 g s/cm3) in foams show no deviation from particles in the axial configuration. Conversion in the radial flow configuration, however, is significantly lower for both reactions. Given the low gas velocities due to a higher cross-sectional area and a shorter length of the catalyst in flow direction, backmixing is presumed to be the cause. For closer examination, experiments were performed to quantify the foam backmixing behaviour by measuring the residence time distribution (RTD). Combining the results, it was possible to establish mixed flow models in agreement with the data, thus suggesting backmixing to be the cause of decreasing conversion. The results of the kinetic study show no effect on the performance comparing fixed bed configurations of particles and foams. Ceramic foams appear well suited as structured catalyst inserts in gas–particle filters, given their low pressure drop and permeability in all flow directions.

Graphical abstractKinetic studies of open-cell foams as catalyst structure address combined effects of reaction and backmixing for low velocity conditions. Simulating the foam as insert in gas–particle filter elements the catalytic conversion of NOx and organic compounds (VOC) is investigated experimentally and by mathematical methods. As a conclusion, the effect of backmixing is quantified in comparison with a fixed bed configuration.Figure optionsDownload full-size imageDownload as PowerPoint slide