Spatially-resolved investigation of the water inhibition of methane oxidation over palladium

Abstract

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.