CO2 conversion to CO by auto-thermal catalyst-assisted chemical looping

A bifunctional 9 wt.%NiO-16 wt.%Fe 2 O 3 /MgAl 2 O 4 material was prepared for CO 2 conversion to CO by auto-thermal catalyst-assisted chemical looping. This process is designed to maximize CO 2 conversion. The generation of CO from CO 2 was investigated between 873 K and 1023 K. The high endothermicity of methane dry reforming and the material deactivation by coke deposition were avoided by the simultaneous feeding of CH 4 , CO 2 and O 2 in a 1:1:0.5 molar ratio during the reduction half-cycle of chemical looping. In this half-cycle, interaction of Ni with Fe leads to Ni-Fe alloy formation. The resulting Ni-based catalyst converts CH 4 + CO 2 + O 2 into a mixture of CO and H 2 , which both reduce Fe 3 O 4 , producing CO 2 and H 2 O. In the CO 2 re-oxidation half-cycle, CO is produced and the Ni-Fe alloy decomposes into Ni and Fe 3 O 4 . The reduction capacity ( R c ) of the gas mixture strongly depends on the ratio R c between reducing and oxidizing gases. Based on thermodynamic calculations, high conversion of Fe 3 O 4 to reduced state can be reached if R c > 2 and T > 873 K. During prolonged auto-thermal chemical looping at 1023 K, the 9 wt.%NiO–16 wt.%Fe 2 O 3 /MgAl 2 O 4 suffers from deactivation in the first five cycles, after which a more stable operation is established. Based on TEM measurements, sintering was found to be the main cause for the initial decrease of CO production.