Ni, Co and Cu-promoted iron-based oxygen carriers in methane-fueled chemical looping hydrogen generation process

Abstract

Oxygen carrier (OC) is essential in methane based chemical looping hydrogen generation (CLHG) process. Fe-based oxygen carriers have attracted lots of attention and attempts have been made to improve the CH4 conversion and hydrogen productivity. However, the influence of different promoters has yet to be compared. In this work, the interaction of promoters (Ni, Co and Cu) with Fe and the feasibility of tiny doping were investigated. Results showed that the oxygen activity and CH4 conversion increased after the addition of Ni, Co and Cu. Ni-promoted oxygen carriers presented the highest CH4 conversion and H2 yield. Co dopant benefitted the oxygen capacity, but Cu dopant restricted the deep reduction of Fe-based oxygen carriers. H2-TPR results revealed the oxygen activity was improved significantly at the intermediate temperature. A low concentration of Ni addition worked on hydrogen productivity as Mg-Fe-Al-O spinel with 1.7 wt% of Ni produced 1.3 mmol/gOC comparing with 1 mmol/gOC for Mg-Fe-Al-O. The promoters also facilitated the Fe segregation from the spinel phase. And the surface sintering of the promoted OCs was more serious, possibly resulting from the impregnation method. These findings could provide guidance for selection of promoters in chemical looping hydrogen generation process fueled by CH4.