Ni based oxygen carrier over γ-Al2O3 for chemical looping combustion: Effect of preparation method on metal support interaction

This study deals with the development of a Ni based oxygen carrier (OC) over La-modified and Co-doped gamma-Al2O3 suitable for a fluidized bed chemical-looping combustion (CLC) process. La is found to stabilize the bulk phase transformation of gamma-Al2O3 whereas Co minimizes the formation of irreducible bulk nickel aluminate. Apart from these beneficial effects, the reducibility and the structural properties of the prepared OCs are found to be modified by the different preparation methods used. The N-2 adsorption isotherm shows that gamma-Al2O3 retains its structural integrity in only one preparation method. Reducibility as determined by consecutive temperature programmed reduction and oxidation techniques resembles the chemical properties of delta- and theta-Al2O3 for the other two preparation methods. However, no bulk phase change is detected for the three OCs using XRD. This suggests that the observed changes occur mainly at the molecularly thin surface layers of the OCs which display structural properties (geometric, electronic, coordination) significantly different from those of the bulk. The prepared OCs are also tested under CLC operating condition of the Chemical Reactor Engineering Center (CREC) fluidized Riser Simulator, using multiple reduction/oxidation cycles. Reactivity results obtained show expected reducibility, oxygen carrying capacity and stability with the three different preparation techniques. (C) 2013 Published by Elsevier B. V.