Enhanced performance of chemical looping combustion of methane by combining oxygen carriers via optimizing the stacking sequences

Abstract Combination of different types of oxides is a general strategy to prepare high performance oxygen carriers (OCs) for chemical looping combustion (CLC) technology. However, the possible chemical interactions among different components during the long-term redox cycling may reduce the stability of OCs. In the present work, we physically combine different types of OC sticks (i.e., CuO/SiO 2 , Fe 2 O 3 /Al 2 O 3 , Mn 2 O 3 /ZrO 2 and NiO/ZrO 2 ) in particular stacking sequences in a fixed bed reactor to improve the CLC performance. The reaction between methane and CuO is exothermic and the CuO/SiO 2 OC exhibits very high activity for methane oxidation and superior resistance to carbon deposition. It is suitable to place the CuO/SiO 2 in the front of the sequence which can sufficiently convert methane, and the heat releasing from this reaction will promote the following endothermic reactions. NiO/ZrO 2 OC also represents very high activity for CH 4 oxidation but results in serious carbon deposition. Since the reduced metallic Ni is an active catalyst for methane activation, it is suggested to place NiO/ZrO 2 in the middle of the sequence to enhance the further conversion of methane and to provide enough space to remove the carbon deposition via the gasification by CO 2 or H 2 O generated from the front reaction. Mn 2 O 3 /ZrO 2 OC possesses poor activity for methane conversion but high resistance to carbon deposition, which can be used to convert unreacted methane in the end of the sequence. Fe 2 O 3 /Al 2 O 3 OC is not an important issue due to the low activity and reaction rate. As a result, the combined OCs with a stacking sequence of CuNiFeMn or FeCuNiMn show high performance in CH 4 conversion (>97%), CO 2 selectivity (>96%), redox stability and resistance to carbon deposition. These results make a certain reference for using the combined OCs in the large-scale CLC system.