Recently, there has been tremendous renewed interest in hydrogen for energy applications due to the potential to be independent from finite fossil fuels and greenhouse gasses emissions. Thermochemical cycles can be used to split water through a series of chemical reactions where the net result is the production of hydrogen and oxygen at much lower temperatures than direct thermal decomposition. Energy is supplied as heat in the temperature range necessary to drive the endothermic reactions and all process chemicals in the system are fully recycled. The sulfur-based family of thermochemical cycles appears promising for producing hydrogen from water.

The sulfur family of thermochemical cycles employs a high-temperature catalytic sulfuric acid decomposition reaction step. The reaction produces oxygen and generates SO2, which is used in other reaction steps of the cycles. The reaction takes place from 750 to 900 °C, or higher, and is facilitated by heterogeneous catalysts to improve the efficiency and safety of the process by increasing the reaction rates and by reducing the reactor size and volume. The Idaho National Laboratory (INL) is currently exploring the limitations of sulfuric acid decomposition catalysts for the purpose of developing highly active, stable catalysts for this reaction step.

Results will be presented for several decomposition catalysts. Reactions were carried out using a feed of concentrated liquid sulfuric acid (96 wt%) at atmospheric pressure at temperatures between 750 and 900 °C and a weight hour space velocity of 50 g acid/g catalyst/hr. Reactions were run at these high space velocities such that variations in kinetics were not masked by excess catalyst. This presentation will provide a comparison of catalyst activities, stabilities, and property changes under decomposition conditions.