Reverse Water Gas Shift by Chemical Looping with Iron-Substituted Hexaaluminate Catalysts

The Fe-substituted Ba-hexaaluminates (BaFeHAl) are active catalysts for reverse water-gas shift (RWGS) reaction conducted in chemical looping mode. Increasing of the degree of substitution of Al(3+)for Fe(3+)ions in co-precipitated BaHAl from 60% (BaFeHAl) to 100% (BaFe-hexaferrite, BaFeHF), growing its surface area from 5 to 30 m(2)/g, and promotion with potassium increased the CO capacity in isothermal RWGS-CL runs at 350-450 degrees C, where the hexaaluminate/hexaferrite structure is stable. Increasing H-2-reduction temperature converts BaFeHAl to a thermally stable BaFeHF modification that contains additional Ba-O-Fe bridges in its structure, reinforcing the connection between alternatively stacked spinel blocks. This material displayed the highest CO capacity of 400 mu mol/g at isothermal RWGS-CL run conducted at 550 degrees C due to increased concentration of oxygen vacancies reflected by greater surface Fe2+/Fe(3+)ratio detected by XPS. The results demonstrate direct connection between CO capacity measured in RWGS-CL experiments and calculated CO(2)conversion.