(600g) NiO/Ce-?Al2O3 Oxygen Carrier for Chemical-Looping Combustion: Reactivity and Stability

This study deals with the development of a Ce modified NiO/Ce-γAl₂O₃ oxygen carrier suitable for a CLC process. In CLC, the most important characteristics of an oxygen carrier are the reactivity, oxygen carrying capacity and stability under cyclic operation [1, 2]. To investigate these matters successive TPR and TPO experiments were developed in the context of the present study. In cyclic TPR/TPO experiments, the reduction and oxidation profiles of NiO/Ce-γAl₂O₃sample remains unchanged and the amount of Ni reduction also shows a stable behavior. Approximately 90 % nickel oxide conversion was achieved using the Ce modified sample, while the value was in the 75 % range for the unmodified carrier. This observation suggests that the addition of Ce helps the formation of easily reducible nickel oxides on the Ce-modified alumina support and minimizes the formation of nickel aluminates (reduces at high temperature only) [3].

The hydrogen pulse chemisorption results (after each TPR cycle) further confirmed the stable behavior of the Ce modified sample. A higher metal dispersion was observed in the Ce modified sample although both the unmodified and modified samples showed a stable metal dispersion with successive redox cycles. This indicates that Ce helps to increase the dispersion of nickel. Thus, the addition of Ce alters the metal surface modifying the degree of interaction between Ni and alumina support, maintaining a consistent metal dispersion during the repeated recox process. It is also apparent that the metal crystal size of the NiO/Ce-γAl₂O₃sample remained unchanged over repeated cycles, an indication of the absence of agglomeration of nickel crystals.

 References

1. M.M. Hossain, H.I. de Lasa, Chem. Eng. Sci., 63 (2008), 4433-4451
2. M.M. Hossain, K.E. Sedor, H.I. de Lasa, Chem. Eng. Sci., 62 (2007) 5464.
3. M. R. Quddus, M.M. Hossain, de Lasa, H.I., Catal. Today (In press).