Utilization of Alumina Aerogel as High Surface Area Support for the Fabrication of Oxygen Carriers in the Chemical Looping Combustion Process

摘要

The chemical looping combustion (CLC) process is a new technology for clean energy generation from fuels. CLC results in streams of pure carbon dioxide and condensable steam, both of which are produced without significant energy consumption. Preparation of suitable oxygen carriers is crucial for the long-term operation of a CLC process. Nickel and iron oxides (NiO and Fe2O3) are promising materials for CLC. NiO is highly reactive, but it has issues with carbon deposition during reduction and with particle agglomeration in its unsupported state. Although Fe2O3 has a slower reactivity, it is an inexpensive oxygen carrier. In this study, alumina aerogel-supported NiO and Fe2O3 were fabricated for methane CLC. The loadings of NiO and Fe2O3 were optimized to obtain good activity and stability during cyclic methane CLC operation. Compared with pure metal oxide oxygen carriers, the supported NiO and Fe2O3 oxygen carriers demonstrated high reduction oxidation rates and superior physical stability. X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy studies suggest that there was a good interaction between NiO and Fe2O3, with high mesoporous surface area support contributing to excellent performance during the CLC process. When calculated based on grams of pure metal oxide, the oxygen capacity of the supported metal oxides was comparable to that of the pure metal oxides. The nature of the fuel affected CLC's activity and stability: NiO was fully reduced to metallic nickel with methane; Fe2O3 was reduced to mixed Fe3O4 and FeO phases. The preparation of alumina aerogel and the fabrication of NiO and Fe2O3 oxygen carriers that support using such alumina are discussed in detail.