The Study of Thermochemical Hydrogen Preparation. III. An Oxygen-evolving Step through the Thermal Splitting of Sulfuric Acid

Abstract

Abstract The thermal decomposition of sulfuric acid is used as a step in the oxygen evolution in some thermochemical water-splitting cycles. The catalytic activity of metal oxides was studied in an attempt to find some suitable catalysts for sulfuric acid decomposition. The catalytic activity of SiO2, Al2O3, ZnO, CuO, NiO, CoO, Fe2O3, MnO, Cr2O3, V2O5, TiO2 was measured at high temperatures (800–870 °C and at atmospheric pressure. Iron(III) oxide was found to have the highest activity as a catalyst. Low catalytic activity was observed for the oxides (Al2O3, ZnO, NiO, CoO, MnO) which change to their sulfates under the present reaction conditions. Since the reaction conditions were very severe (more than 800 °C and in the presence of steam), a rapid decrease in both the specific surface area and the catalytic activity was observed. In order to avoid these disadvantages and in order to prepare practically useful catalysts, iron(III) oxide was pelletized and sintered (1000 °C, 6 h). Upon this procedure, this catalyst showed an almost constant activity for 120 hours’ reaction.