Rapid Production of Hydrogen and Carbon Monoxide via the Heterogeneous Oxidation of Zn(g)

The heterogeneous oxidation of Zn(g) is considered as an improved approach to the production of H₂ and CO in the two-step Zn/ZnO solar thermochemical cycle. The rate of Zn(g) oxidation by H₂O and CO₂ is measured gravimetrically in a quartz tubular flow reactor for temperatures between 800 and 1150 K, Zn(g) concentrations up to 36 mol%, and H₂O/CO₂ concentrations up to 45 mol%. The rate of the heterogeneous oxidation of Zn(g) by both H₂O and CO₂ is on the order of 10⁻⁸–10⁻⁵ mol cm⁻² s⁻¹. For similar oxidizing conditions, H₂O oxidizes Zn(g) three times as fast as CO₂, indicative of a lower heterogeneous oxidation activation energy in the H₂O system. Less than one second is required to convert more than 85% of Zn to ZnO for all temperatures in both the H₂O and CO₂ reacting systems.