Complete methane oxidation over Ba modified Pd/Al2O3: The effect of water vapor

The effect on complete methane (CH4) oxidation activity by an addition of up to 2 wt.% barium (Ba) promoter to alumina supported palladium (Pd/Al2O3, 2 wt.% Pd) was investigated. The catalyst samples were characterized with various techniques; temperature programmed oxidation (TPO), temperature programmed reduction with CH4 (CH4-TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Flow reactor was used to investigate the CH4 oxidation activity in the presence and in the absence of water vapor and also to evaluate the possibility to regenerate the catalytic activity after water vapor exposure. The results from the TPO and the CH4-TPR experiments together with the XPS analysis gave no evidences for electronic promotion of the catalytic activity by addition of 0.5-2 wt.% Ba. This goes in line with the CH4 conversion in dry gas condition, which was not affected by the Ba addition. However, we observed that an addition of Ba to Pd/Al2O3 enhances the CH4 oxidation activity in the presence of water vapor, hence mitigates the effect of water deactivation. Interestingly, it was also seen that after water vapor exposure, the CH4 oxidation activity could be regenerated to greater extent for the Ba promoted samples, particularly for the regeneration temperatures of 500-600 degrees C. Our results clearly show that the support influences the water deactivation of the active palladium sites and that the addition of barium is beneficial for the catalyst regeneration.