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.

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