Chemical Looping Combustion over Yolk–Shell-Type Alumina-Based Oxygen Carrier: Catalytic Structure and Process Activity

Abstract

Chemical looping combustion (CLC) is an innovative cyclic process for fuel combustion to intrinsically separate carbon dioxide. In this process, oxygen and fuel are contacted by an intermediate oxygen carrier (OC), a metal oxide/metal that can alternately be reduced and oxidized. In this study, a yolk (Al2O3)–shell (ZrO2) was synthesized as the support of the OC and 20 wt % copper oxide was impregnated on the surface of it. The structure and cyclic reduction–oxidation (redox) performance of the CuO-impregnated yolk–shell sample were compared with those of CuO-impregnated core (Al2O3)–shell (ZrO2) and CuO-impregnated alumina oxygen carriers in the CLC process. The synthesized OCs were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX) dot mapping. A homogeneous coating of the zirconia on the alumina was obtained for the yolk–shell material. The pore size distribution became narrow in the presence of the zirconia coating. Furthermore, a yolk–shell architecture prevented the contact between the yolk (Al2O3) and the copper oxide materials, and CuAl2O4 spinel formation was inhibited. The obtained results showed that the oxygen transport capacities of the 20CuO/Al–C@Zr (yolk–shell support), 20CuO/Al@Zr (core–shell support), and 20CuO/Al oxygen carriers are 3.80, 3.47, and 3.4 wt %, respectively. The oxygen carrier with the yolk–shell support exhibited the highest activity, oxygen transport capacity, and coke formation resistance.