Chromium-induced deactivation of a commercial honeycomb noble metal-based CO oxidation catalyst

• A honeycomb catalyst used to treat the exhaust of a SOFC system was characterized.
• CO oxidation activity decreased due to chemical (Cr) and thermal aging.
• Thermal aging (sintering) alone had only a limited influence on activity.
• Cr-containing deposits could maintain acceptable CO conversion under dry conditions.
• Chromium oxyhydroxide species with very low activity formed in presence of water.

A commercially available honeycomb CO oxidation catalyst used to control the exhaust of a solid oxide fuel cell (SOFC) based power system has been characterized after prolonged use. X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, N2 physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to determine the phase composition, the morphology and the chemical state of the various components. Besides sintering of the active phase, deactivation was found to occur mainly as the result of the deposition of chromium-containing species on the catalyst washcoat. These fouling species mainly appeared as highly crystalline Cr2O3 particles and could still maintain acceptable CO oxidation activity under dry atmosphere. However, the formation of surface chromium oxyhydroxide species was found to occur in the presence of water vapor, leading to significant catalyst deactivation.

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