The heterogeneous oxidation of Zn(g) is a promising reaction pathway for the conversion of CO2 into CO in the two-step Zn/ZnO solar thermochemical cycle as it eliminates the solid-state diffusion limitation that plagues the oxidation of Zn(l,s). The rate of the heterogeneous oxidation of Zn(g) is measured gravimetrically in a quartz tubular flow reactor operated at atmospheric pressure for temperatures between 800 and 1150K, Zn(g) concentrations up to 36mol%, and CO2 concentrations up to 45mol%. The surface kinetics are extracted from the global reaction rate using a numerical reacting flow model that accounts for the transport of reacting species in the gas phase. The oxidation of Zn(g) by CO2 is rapid, on the order of 10-8-10-5molcm-2s-1, and the rate is proportional to the product of the Zn(g) and CO2 partial pressures at the reaction surface. The activation energy for the Arrhenius reaction rate parameter is 44±3kJmol-1 and the pre-exponential factor is (92±6)×10-3molcm-2s-1atm-2. As a result of the rapid rate of oxidation of Zn(g), less than 1s is required to convert more than 85% of Zn to ZnO.
- Mass transfer
- Metal oxidation