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The poisoning effect of I -/I 2 mixtures on ferrous oxide based catalysts was investigated. These catalysts were used in the sulfuric acid thermal decomposition that is the highest endothermic step in the sulfur-iodine thermochemical cycle for hydrogen production by water splitting. This decomposition reaction needs a temperature as high as 1100 K to occur with a convenient thermodynamic yield for SO 2 formation, and it is affected by kinetic limitations. Therefore only the use of a suitable catalyst allows for a large decrease in the H 2 SO 4 decomposition temperature and attaining reaction yields close to the thermodynamic limits. I 2 and HI present even in traces in the sulfuric acid feeding stream could lead to the poisoning of the catalyst used for the decomposition process and must therefore be minimized. In this study, two Fe 2 O 3 catalysts supported on quartz wool and on alumina were used in the temperature range 873-1073 K in ordinary pressure conditions. The SO 2 formation rates were measured before and after the catalyst poisoning. Kinetics measurements and scanning electron microscopy (SEM) analysis show that I -/I 2 contamination reduced the catalytic activity by modifying its surface properties.

The Bunsen reaction identifies the chemical formation of sulfuric acid and hydriodic acid when sulfur dioxide is oxidized by molecular iodine in aqueous solutions. This reaction occurs spontaneously in a temperature range of 293-373 K and is one of the three steps of the sulfur-iodine thermochemical cycle capable of producing hydrogen from water. In order to attain this, the handling of the H 2 SO 4 /HI mixture is crucial for the thermal decompositions which follow. In our study, we propose an innovative way to separate the acids by using an intermediate insoluble sulfonic acid which forms during the process. This procedure results in two main advantages: (1) the common problem of large quantities of iodine in excess is avoided and (2) less water is used.