Ce stabilized Ni–SrO as a catalytic phase transition sorbent for integrated CO2 capture and CH4 reforming

Abstract

Integration of carbon dioxide capture from flue gas with dry reforming of CH₄ represents an attractive approach for CO₂ utilization. The selection of a suitable bifunctional material serving as a catalyst/sorbent is the key. This paper reports Ni decorated and CeO_x-stabilized SrO (SrCe_0.5Ni_0.5) as a multi-functional, phase transition catalytic sorbent material. The effect of CeO_x on the morphology, structure, decarbonation reactivity, and cycling stability of the catalytic sorbent was determined with TEM-EDX, XRD, in situ XRD, CH₄-TPR and TGA. Cyclic process tests were conducted in a packed bed reactor. The results indicate that large Ni clusters were present on the surface of the SrNi sorbent, and the addition of CeO₂ promoted even distribution of Ni on the surface. Moreover, the Ce–Sr interaction promoted a complex carbonation/decarbonation phase-transition, i.e. SrCO₃ + CeO₂ ↔ Sr₂CeO₄ + CO₂ as opposed to the conventional, simple carbonation/decarbonation cycles (e.g. SrCO₃ ↔ SrO + CO₂). This double replacement crystalline phase transition mechanism not only adjusts the carbonation/calcination thermodynamics to facilitate SrCO₃ decomposition at relatively low temperatures but also inhibits sorbent sintering. As a result, excellent activity and stability were observed with up to 91% CH₄ conversion, >72% CO₂ capture efficiency and ∼100% residual O₂ capture efficiency from flue gas by utilizing the CeO₂ ↔ Ce₂O₃ redox transition. This renders an intensified process with zero coke deposition. Moreover, the SLDRM with SrCe_0.5Ni_0.5 has the flexibility to produce concentrated CO via CO₂-splitting while co-producing a syngas with tunable H₂/CO ratios.