Effects of water vapor and temperature upon combustion stability of CeZrO2-modified Pd-Pt/Al2O3 catalyst

Abstract

Two bimetallic Pd-Pt catalysts were prepared by wash-coating the composites of Pd-Pt/CeZrO2-Al2O3 onto cordierite monolith and they were evaluated in a tubular reactor for stability in combustion of SOFC stack flue gas at GHSV 29,280 h−1 and 1 atm. The Pd-rich catalyst showed better stability than the Pt-rich catalyst for combustion of the wet feed. Water vapor in the stack flue gas affected the catalyst activity adversely via the formation of inactive Pd(OH)2 species at the reaction temperatures of 723 and 823 K, but this effect was eliminated by raising the temperature to 923 K or above. Catalyst properties such as specific surface area, pore size and metal dispersion did not deteriorate significantly after combustion of the wet feed in the temperature range of 723-1,023 K. The presence of CeZrO2 in Al2O3 material was considered to affect the support properties favorably, leading to a kind of metal-support interaction beneficial for the combustion of the wet feed. This interaction helped to enable the Pd-Pt catalysts to maintain good stability for combusting the wet SOFC stack flue gas with the stoichiometric air-to-fuel ratio at 923 K or above.