Deactivation Mechanisms of Platinum/Titania Catalysts for Sulfuric Acid Decomposition in Sulfur-Iodine Thermochemical Water-Splitting Cycles

Lucia M. Petkovic1, Harry W. Rollins1, Patrick J. Pinhero2, Kyle C. Burch1, Daniel M. Ginosar1, and Helen H. Farrell2. (1) Chemical Sciences, INL, P.O. Box 1625, Idaho Falls, ID 83415-2208, (2) Material Sciences, INL, P.O. Box 1625, Idaho Falls, ID 83415-2218

Thermochemical cycles consist of a series of chemical reactions to produce hydrogen from water at lower temperatures than by the direct thermal decomposition. When the primary energy source to drive the cycle is nuclear or solar heat, hydrogen can be produced without the need of fossil fuels and without generating gasses considered to be responsible for global warming. Among the high number of thermochemical water-splitting cycles proposed in the literature, the group that include the sulfuric acid decomposition reaction appears to be the most feasible. Both high temperatures and catalysts are required for decomposing sulfuric acid at industrially significant reaction rates and high levels of chemical conversion and energy efficiency. Preliminary work performed at the Idaho National Laboratory found that Pt supported on low surface area titania was relatively more stable than higher surface area alumina or zirconia supported catalysts over short duration testing under realistic reaction conditions. For the work reported here, a commercially-available low-surface-area titania supported platinum catalyst was submitted to flowing concentrated sulfuric acid at 1123 K for different times on stream up to about 23 days. Factors that caused catalyst deactivation will be discussed in light of the results of a number of experimental and spectroscopic analyses performed on the spent catalyst samples and computational modeling of metal loss due to sintering and sublimation.