Pt/TiO₂ (rutile) catalysts for sulfuric acid decomposition in sulfur-based thermochemical water-splitting cycles

Thermochemical cycles consist of a series of chemical reactions to produce hydrogen from water at lower temperatures than by direct thermal decomposition. All the sulfur-based cycles for water splitting employ the sulfuric acid decomposition reaction. This work reports the studies performed on 1 wt% Pt/TiO₂ (rutile) catalysts submitted to flowing concentrated sulfuric acid at 1123 K and atmospheric pressure for different times on stream between 0 and 548 h. Catalyst activity showed an initial decrease that lasted for about 66 h, followed by a slight recovery of activity between 66 and 102 h TOS, and a period of slower deactivation after 102 h TOS. Catalyst sulfation did not seem to be detrimental to catalyst activity. The activity profile suggested that a complex dynamic situation, involving platinum sintering, volatilization, and oxidation, along with TiO₂ morphological changes, affected catalyst activity in a non-monotonic way.