(182c) Sulfuric Acid Decomposition Catalysts and Reaction Considerations for Sulfur-Based Thermochemical Water Splitting Cycles

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 recycled. The sulfur-based family of thermochemical cycles appears promising for producing hydrogen from water. These cycles employ a high-temperature 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. The overall energy efficiency of the hydrogen production process is directly correlated to the temperature of the sulfuric acid reaction step.

Current catalyst stability studies performed at the Idaho National Laboratory (INL) have found that the most active catalysts for the acid decomposition reaction, platinum supported on porous metal oxides, are not stable at the higher reaction temperatures. Some alternative complex metal oxide catalysts, including spinels and perovskites, have lower activity, but appear to have better high-temperature stability. This presentation will provide data on temperature-dependent catalyst stabilities and discuss reaction considerations for achieving high energy conversion efficiencies.