Zeolite-Supported Iron Oxides as Durable and Selective Oxygen Carriers for Chemical Looping Combustion

Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion with inherent CO, separation from flue gases, circumventing high cost for CO, capture and NOx elimination as in conventional combustion processes. Metal oxides are commonly used as oxygen carriers (OCs) in CLC. However, sintering and coking of OCs and the consequent degradation in their activity and durability during multiple cycles inhibit the practical applications of CLC technology. In the present study, we employed a silicalite-1 zeolite support to achieve OCs with high resistance against sintering and coking in CLC. Iron oxides (Fe2O3) with methane fuel were employed to demonstrate the approach and to quantify the influence of silicalite-1 support on conversion efficiency, durability, and selectivity of these OCs in CLC cycles. Two iron oxide zeolite geometrical structures, a core shell Fe2O3@silicalite-1 and a Fe2O3-impregnated silicalite-1 (Fe2O3/silicalite-1), were created to improve Fe2O3 stability. The CLC tests showed that both structures led to less aggregation of Fe2O3 OCs at 1223 K. A comparison between Fe2O3/silicalite-1 and Fe2O3@silicalitc-1 in CLC tests illustrates that Fe2O3 impregnated in zeolite had higher durability than in the core shell structure. The selectivity of CH4 to CO, followed the order of Fe2O3/silicalite-1 > Fe2O3@silicalite-1 >> bare Fe2O3. The high selectivity of Fe2O3/silicalite-1 to CO, in CLC tests can be attributed to the encapsulation of Fe2O3 inside channels of silicalite-1 that provides physical barriers for aggregation of OCs in CLC cycles as well as coke deposition on OCs. In conclusion, our study of the structure function relation for silicalite-1-supported Fe2O3 OCs can form the basis for the development of silicalite-1 as an efficient support in chemical looping applications.