Enhancement of iron-based oxygen carriers through alloying with tungsten oxide for chemical looping applications including water splitting

Chemical looping applications offer a variety of options to decarbonise different industrial sectors, such as iron and steel and hydrogen production. Chemical looping with water splitting (CLWS) is a chemical looping technology, which produces H₂ while simultaneously capturing CO₂. The selection of oxygen carriers (OCs) available to be used in CLWS is finite, due to the thermodynamic limitations of the oxidation with steam for different materials at the relevant process temperatures. Iron-based materials are one of the most widely studied options for chemical looping combustion (CLC), touted for their relative abundance and low cost; likewise, for CLWS, iron is the most promising option. However, when the reduction of iron oxide (Fe₂O₃) is extended to wüstite (FeO) and iron (Fe), agglomeration and sintering problems are the main challenge for fluidisation.

This work presents iron and tungsten mixed oxides as the OCs for a family of chemical looping applications. The OCs were produced via co-precipitation; performance assessment was conducted in a thermogravimetric analyser and a lab-scale fluidised bed reactor over continuous redox cycles. The use of tungsten combined with iron results in a solid solution of tungsten within the Fe₂O₃ matrix that produced a more mechanically stable material during operation, which performed well during multiple redox cycles with no apparent decrease in the oxygen transport capacity and showed no apparent agglomeration. Furthermore, materials containing tungsten showed a resistance to carbon deposition, whereas the reference Fe₂O₃ showed peaks of CO and CO₂ during the oxidation period, thus indicating carbon deposition. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.