Reactivity and stability of Ni/Al₂O₃ oxygen carrier for chemical-looping combustion (CLC)

Chemical-looping combustion (CLC) is a technology that reduces the carbon dioxide emissions from fossil fuel power stations. A nickel supported on α-alumina oxygen carrier is investigated in this study, for use in a CLC process. Oxygen carriers with various nickel loadings on alumina are prepared according to the incipient wetness technique. The reactivity and stability of the prepared oxygen carrier samples, during repeated reduction-oxidation cycles, is demonstrated using temperature programmed reduction and oxidation. Pulse chemisorption results show that the dispersion and active crystallite diameter of the nickel particles remain constant over multiple reduction-oxidation cycles, indicating that no agglomeration occurs up to a nickel loading of 20 wt% supported on alumina. The stability and reactivity of the oxygen carriers, under industrial relevant conditions, are also investigated using the CREC fluidized bed riser simulator. It is observed that a 20 wt% nickel supported on alumina oxygen carrier is stable under industrial relevant fluidized bed reaction conditions, converting 76% of methane to carbon dioxide and water vapor, the combustion products. The metal support interaction is assessed by H₂ temperature programmed desorption, which shows that the metal-support interaction decreases as more nickel is loaded onto the alumina support.