Spatially-resolved investigation of the water inhibition of methane oxidation over palladium†
Pd/Al2O3 catalysts are known to be active for the low temperature methane oxidation reactions, however it has been shown that a number of gases normally associated with methane gas streams (H2O, CO2, H2S) can have an inhibitory effect on the total oxidation reaction. This work focuses on the effect of H2O on the complete oxidation of methane on a 3%Pd/Al2O3 wash-coated monolith, with a view to understanding the reaction and inhibition mechanisms and their interplay with heat and mass transport phenomena in the monolith. Steady state furnace temperatures of 400 °C, 425 °C and 450 °C, in conjunction with a spatially resolved capillary inlet mass spectrometry (SpaciMS) approach, were employed to test the spatial effect of 0–10% H2O feed concentrations and temperature on complete methane oxidation reactions. 12 sets of experimental intra-catalyst axially resolved gas temperature and concentration profiles were obtained in a central monolith channel and were used to screen a number of postulated global kinetic models, utilising an in house parameter estimation routine developed using Athena Visual Studio v.14.2. A 1D heterogeneous single channel reactor model has been incorporated into the model imposing a gaseous temperature spline to improve the confidence in parameter estimation. The Akaike information criterion (AIC) was used to discriminate between a number of hypothesised global kinetic models, with a newly derived 2 site model demonstrating the best statistical fit.