H₂ Generation from H₂O and H₂S through an Iodine Cycle

During an investigation of thermochemical methods of H2 generation from H2S, we observed the formation of unexpected products according to the reaction, H2S + 3I2 + 2H2O → 6HI + SO2. When coupled with the well-known catalyzed decomposition, 2HI → H2 + I2, this enables the formation of 3H2 per H2S reacted according to the reaction, H2S + 2H2O → 3H2 + SO2. Restated, these two reactions together accomplish the splitting of H2O driven by the oxidation of H2S into SO2. This unexpected chemistry was explored experimentally and computationally revealing a concentration dependent branching between oxidized and elemental sulfur products. The factors affecting the final state of sulfur and the stoichiometry of the products are discussed along with their implications for H2 production, especially in a refinery setting. Hydrocarbon desulfurization is currently a major consumer of H2, but with this newly discovered chemistry, it could become a net H2 producer. This change could reduce CO2 emissions by tens of millions of tons per year