(190d) Reverse Water Gas Shift Chemical Looping for Carbon Dioxide Conversion to Carbon Monoxide on Reduced Perovskite Oxides

Previously, we have shown that from the (La,Sr)CoO₃ perovskite family, La_0.75Sr_0.25CoO₃ was optimum in the reduction of CO₂ to CO because of its structure stability and maximized CO formation at the lowest temperatures. This perovskite was used in the reverse water gas shift chemical looping process (RWGS-CL) for the conversion of carbon dioxide to carbon monoxide that can later be hydrogenated to liquid fuels. In the RWGS-CL process, a stream of H₂ reduces the La_0.75Sr_0.25CoO₃ perovskite. Then, CO₂ is flowed and converted to CO on the reduced oxides.  Temperature-programmed (H₂-TPR, CO₂-TPO) and isothermal CO₂ conversion experiments were performed on the perovskite to determine the optimum operating temperatures for the H₂-reduction (500 °C) and CO₂-conversion (850 °C) steps.

The RWGS-CL process was studied for three reaction cycles. After the second cycle, the RWGS-CL exhibited stability of the crystalline structures and constant CO production rates (as high as 172.6 mol of CO/ grams of perovskite /min).

The cyclic nature of the process presents an advantage over the reverse water gas shift (RWGS) reaction, because with separate H₂ and CO₂ streams, methane formation is suppressed. Furthermore, the materials remain stable after the second step, whereas catalysts used for RWGS generally deactivate. The high CO formation rates and the repeatability of the process make RWGS-CL a promising technology for CO₂ conversion that could produce hydrocarbons, if a renewable hydrogen source is available.