Effects of Support on the Performance of NiO-Based Oxygen Carriers

Abstract

The performance of an oxygen carrier for Chemical Looping Combustion varies with the support material used. NiO oxygen carriers were prepared using 60 or 70 wt% NiO and different raw support materials (<i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/>, pseudoboehmite, <i>α<i/>-Al<sub>2<sub/>O<sub>3<sub/>, <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/> mixed with MgO, hydrotalcite, MgAl<sub>2<sub/>O<sub>4<sub/>, and <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/> with added graphite) by the mechanical mixing method. Reactivity tests were conducted using a thermogravimetric analyzer (TGA) at 950˚C. The oxygen carriers prepared using <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/>, <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/> mixed with a small amount of MgO, hydrotalcite, and MgAl<sub>2<sub/>O<sub>4<sub/> showed high oxygen transfer capacity, high oxygen utilization, and a high oxygen transfer rate. Graphite addition to <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/> did not increase the surface area or reactivity. The use of pseudoboehmite as a support led to a significant decrease in oxygen transfer capacity and severe agglomeration of the oxygen carriers during the redox reaction. The increase in MgO content in the raw support materials decreased the reduction reactivity. The oxygen carriers prepared with <i>α<i/>-Al<sub>2<sub/>O<sub>3<sub/> showed less oxygen transfer capacity than the other oxygen carriers. The differences in the reactivity according to the support type were explained by the relative strength of NiO-support interaction obtained from the temperature-programmed reduction analysis. The reactivity test results in this work indicate that <i>γ<i/>-Al<sub>2<sub/>O<sub>3<sub/> and hydrotalcite could be desirable raw support materials to prepare highly reactive NiO oxygen carriers with high NiO content.