Thermal stability study of NiAl2O4 binders for Chemical Looping Combustion application

Abstract The influence of the preparation method of NiAl 2 O 4 binders on their thermal stability was studied. For this purpose, the reactivity of two different NiAl 2 O 4 binders with CO as fuel was studied in a fixed bed reactor device. Successive oxidation–reduction cycles were performed on the two binders to study their reactivity with the fuel and their structural modifications as cycles proceed. Results reveal that binders are not inert in reducing atmosphere; they both react with the fuel to produce CO 2 . The total reduction capacity (TRC) of the first binder (B1, synthetized by pyrolytic pulverization) increases during the first cycles and levels off after 20 cycles. However, the TRC of the second binder (B2, synthetized by calcination of a mixture of Ni(OH) and γ-Al 2 O 3 ), increases progressively and reaches a maximum after 80 cycles. The growing amount of available oxygen in the binders leads both binders to structural modifications. X-ray Diffraction studies performed on fresh and aged binders presented a shift of the peaks related to NiAl 2 O 4 . Moreover, quantitative X-ray Diffraction studies and Temperature Programmed Reduction measurements were performed in order to quantify the NiO present in each binder before and after oxidation–reduction cycles. These experiments revealed the presence of NiO in fresh binders due to the preparation method, and an increase of this amount after oxidation–reduction cycles. Therefore, NiAl 2 O 4 in the binder is progressively decomposed producing NiO and Al 2 O 3 . Finally, the decomposition of the binder NiAl 2 O 4 as cycles proceed was also observed in studies performed on the oxygen carrier NiO/NiAl 2 O 4 . This work showed that the binder reacts with the fuel and therefore it can contribute to the modification of the oxygen carrier reactivity.