Effects of transition metal dopants on the calcination of CaCO3 under Ar, H2O and H2

This study compares thermal decomposition of pure and transition metal-doped (Fe, Co, Ni, Cu, and Zn) calcium carbonate samples under ˜0.1 mbar of Ar, H2O, and H2 in order to evaluate the effects of doping on CO2 release and conversion. All samples were synthesized via precipitation methods at room temperature from calcium chloride and sodium carbonate precursors, with additional doping of the relevant transition metal chloride. Structural and compositional analysis of the as-prepared and calcined materials is presented. TM-doping results in an earlier onset of CO2 release as compared to Pure CaCO3 irrespective of calcination gas. Cu-doping induced the largest temperature reduction. Calcination in H2O produces an additional lowering of the release temperature, as compared with calcination in Ar, with the Zn-doped sample exhibiting the largest enhancement. During calcination in H2, the Ni-, Co- and Fe-doped samples produce a significant enhancement of CO2 to CO conversion, whereas the overall conversion by the Cu- and Zn-doped samples remained comparable to that of Pure CaCO3. The Ni-doped samples, which produced the highest CO2 conversion, showed the largest comparative enhancement when the calcination gas was changed to H2.