Co - Ni / Al₂ O₃ oxygen carrier for fluidized bed chemical-looping combustion: Desorption kinetics and metal-support interaction

This study was aimed at developing a suitable oxygen carrier for fluidized bed chemical-looping combustion (CLC) processes. To this end a Co promoted Co - Ni / Al₂ O₃ carrier material was synthesized and evaluated. The reactivity of the solid carrier material was assessed by investigating the energetics and kinetics of metal-support interaction using temperature programmed H₂ desorption technique. The estimated activation of energy of hydrogen desorption for Co - Ni / Al₂ O₃ was found to be less than that of unpromoted Ni / Al₂ O₃ samples. This result suggested that doping the fluidizable oxygen carrier with Co decreases the metal-support interaction and the binding energies between the metals and the H₂ molecules, with this playing a significant role to increase the activity of such material. The reactivity and stability of the prepared oxygen carrier particles, under repeated reduction/oxidation cycles, was established in a CREC riser simulator using CH₄ and air for the reduction and oxidation cycles, respectively. Over multiple CLC cycles, the Co - Ni / Al₂ O₃ particles displayed excellent reactivity and stability with minimum changes in metal dispersion and crystallite size. Thus, it is concluded that Co might promote the performance of Co - Ni / Al₂ O₃ particles by reducing the metal-support interactions, as assessed using temperature programmed H₂ desorption. This reduced interaction has a favorable effect on the oxygen carrier reactivity during the oxidation and reduction reactions.