###### Abstract
Pre-combustion capture costs can be potentially reduced as membrane technology advances (with simpler fabrication methods from cheaper raw materials yielding enhanced performances, as studied by [PERSON] et al. [13; 14]) by simplifying the separation processes (PSA and MDEA unit). Alternatively, the use of cheap adsorbents from waste-derived materials can increase the competitiveness of post-combustion capture [15], avoiding costly absorption systems. On the other hand, Chemical Looping Combustion (CLC) first proposed by [PERSON] et al. offers the possibility of avoiding this large energy penalty by combusting a carbonaceous fuel with inherent CO2 capture [16]. This is achieved by splitting the combustion reaction into two steps. CLC exposes a metallic oxygen carrier to oxidizing (e.g., air) and reducing (e.g., natural gas) streams in two separate reactors to avoid the mixing of the combustion products (CO2/H2O) with N2. The oxygen carrier is hydrodynamically transported from one reactor to another, typically operating under fluidization conditions for efficient heat transfer. Alternative to full combustion of natural gas, Chemical Looping Reforming (CLR), developed by [PERSON] et al., obtains an H2-rich syngas stream in the reduction outlet [17]. Subsequent water gas shift and CO2 removal with MDEA is still required, as modeled by [PERSON] et al. [18]. Membrane-assisted chemical looping reforming (MA-CLR) has been proposed by [PERSON] et al. as an effective way to practically eliminate the energy penalty of CO2 capture [11], but still requires several more development steps to de-risk and commercialize the complex system consisting of a membrane operating in a fluidized environment. Furthermore, a critical factor that hinders chemical looping applications is the slow scale-up under pressurized conditions required for efficient integration in power and chemical processes [19]. To overcome this challenge and avoid the operational difficulty of solids transportation between reactors, the gas switching (GS) technology has been suggested as a promising solution by [PERSON] et al. [20]. Syngas production through the gas switching concept was experimentally demonstrated by [PERSON] et al. [21]. The oxygen carrier remains in the same reactor vessel while it is exposed alternatively to reducing, oxidizing and reforming steps by switching the feed and product streams by means of high-temperature valve mechanism. Gas Switching Reforming (GSR) appears as a highly attractive technological candidate for a step-change in H2 production with CCS as shown by [PERSON] et al. [22], in which the reforming (H2 production) and reduction (heat supply) steps are intrinsically decoupled, allowing for effective integration with the pressure swing adsorption unit (PSA), as suggested by [PERSON] et al. for packed bed dynamically operated reactors [23]. Very attractive prospects in terms of efficiency and emissions avoidance, with compelling economic assessment results carried out by [PERSON] et al. suggest that further research and development should be conducted [24]. The oxygen carrier is central to every chemical looping process, and its activity, selectivity and long-term stability are important to ensure high overall process efficiency. Many different types of oxygen carriers have been investigated experimentally for chemical looping reforming, most of them based on iron oxide. [PERSON] et al. investigated iron oxide supported on gamma-alumina particles and found that the addition of nickel was beneficial to achieve a higher conversion of the methane (which was used as a surrogate for natural gas) than pure iron oxide at 800 \({}^{\circ}\)C [25; 26]. Similar observations were made by [PERSON] et al. when adding small amounts (\(\sim\)1 wt.%) of nickel or yttrium to the oxygen carrier [27; 28]. In contrast, the partial substitution of iron oxide with ceria did not improve the performance significantly [26].