(230c) Decomposition of Sulfuric Acid to Produce Sulfur Dioxide and Oxygen in Is Cycle

IS (Iodine-Sulfur) cycle has been considered to be a good candidate for hydrogen production by water splitting using a VHTR (very high temperature nuclear reacator). The IS cycle consists of the following step reactions:

H₂SO₄-> H₂O + SO₃ + 1/2 O₂ for sulfric acid decomposition

I₂ + SO₂ + 2 H₂O -> 2HI + H₂SO₄ for bunsen reaction

2HI -> H₂ + I₂ for hydrogen iodide decomposition

The discussion about the sulfuric acid decompsotion will given in this study. Sulfuric acid decomposer plays a role to absorb the nuclear energy. Sulfuric acid decomposition consists of two reactions in series:1) decomposition of sulfuric acid to sulfur trioxide, 2)decomposition of sulfur trioxide to sulfur dioxide. It was monitored by IR that sulfuric acid can be decomposed without cataysts in gas cell. Sulfuric acid was decomposed to thermodynamic equilibrium conversion level within a few minutes even at 400 ^oC. The kinetic study of sulfuric acid decomposition into sulfur trioxde was conducted by IR and NIR. Sulfur trioxide decomposition can be done by catalytic reaction. IR observation of intermediate adsorbed on catalysts showed that metal sulfate formed on the surface of catalysts. TPD experiments of metal sulfates showed that sulfur dioxide and oxygen was evolved by the decomposition of metal sulfate. From this observation, it was suggested that decomposition of sulfur trioxide on metal oxide catalysts could be done by the process of 1)metal sulfate formation and 2) metal sulfate decomposition. To choose best catalysts, TPD and DTA experiments were done with various metal oxides (Fe, Cu, Cr, Ni, Al, Ti, Mn). The metal oxide with the lowest metal sulfate decomposition among the tested samples was Fe and Cr, while copper oxide and ferric oxide showed the highest activity for sulfur trioxide decomposition at the temperature below 850 ^oC and and above 850 ^oC, respectively. From the above observation, Ferrite catalysts such as Cu-Ferrite, Sr-Ferrite, Cu-Mn ferrite and Ni-Ferrites were prepared for the activity test. It was observed that Cu-Ferrites was the highest metal oxide catalyst for sulfur trioxide catalysts. The Cu-ferrite activity was compared with 1 wt% loaded Pt and Rh catalysts. The experiments showed that the activity of Cu-ferrite was higher than that of the Pt adn Rh catalysts.