Catalyst-assisted chemical looping auto-thermal dry reforming: Spatial structuring effects on process efficiency

Abstract

Catalyst-assisted chemical looping auto-thermal dry reforming (CCAR) is an environment-friendly energy conversion process, performed over a reactor bed with double function, composed of a catalyst and an oxygen storage material (OSM). It converts CH4 and CO2 into industrial syngas, while simultaneously utilizing CO2 from the atmosphere. Two reactor bed configurations were tested, based on the concept of double- and single-zone distribution of catalyst and OSM. Combinations of core-shell structured materials were applied, such as Ni/ZrO2@ZrO2 catalyst, Fe2O3/ZrO2@ZrO2 OSM and Fe/Zr@Zr-Ni@Zr bifunctional catalyst, to assess the spatial structuring at both reactor bed and pellet scale. Samples from different reactor beds were characterized before and after use by ex- or in-situ XRD, N2 adsorption, XPS and STEM-EDX. 25 redox cycles of CCAR were performed to investigate the effect of spatial structuring on the activity and stability. The Fe/Zr@Zr-Ni@Zr bifunctional catalyst possesses higher activity and stability for catalytic CH4 conversion in the reduction half-cycle than the Ni/ZrO2@ZrO2 catalyst due to its small Ni particle size (<3 nm), high carbon resistance and thermal stability of the eccentric core-shell structure. A double-zone bed with Ni/ZrO2@ZrO2 catalyst and Fe2O3/ZrO2@ZrO2 OSM has a similar activity as a single-zone bed for producing syngas in the reduction half-cycle, but it presents a higher CO yield in the re-oxidation half-cycle. This is due to the full use of the oxygen storage capacity of the OSM achieved by complete reduction of Fe3O4 and the avoiding of Ni-Fe alloy formation during the reduction half-cycle. A double-zone bed with bifunctional catalyst and OSM combines both advantages. It provides the highest activity and stability for auto-thermal dry reforming and the highest oxygen storage capacity for CO2 utilization, offering a promising reactor technology for the CCAR process.