Chemical Looping-Based Oxidative Dehydrogenation of Ethane and Successive CO<sub>2</sub> Activation on Fe-Modified CeZrO<i>x</i> Mixed-Metal Oxides
Seong Jin Hong, Bison Seo, Jong Wook Bae
Abstract
Fe-modified CeZrO x bimetal oxides with 5–7 wt % Fe revealed higher catalytic activity for chemical looping-based dehydrogenation of ethane (CL-ODH), with successive activation of carbon dioxide due to the abundant lattice oxygen species. Optimal Fe modification on the Ce–Zr solid solution (Ce 0.5 Zr 0.5 O 2 phase) with 5 wt % Fe was responsible for enhanced selectivity to C 2 H 4 (10.7% yield of C 2 H 4 at 600 °C with a turnover frequency (TOF) value of 0.049 s –1 ). This was carried out by oxidative dehydrogenation of ethane with successive CO 2 activation to form CO by a reverse Boudouard reaction or oxidation of partially reduced active metal oxides (oxygen-vacant sites), which was attributed to the enhanced thermal stability of Fe( x )CeZrO x catalysts. An excessive amount of iron oxides above 7 wt % Fe on the Ce–Zr bimetal oxides led to thermal agglomeration of iron oxides, resulting in an increased CO x byproduct formation during C 2 H 6 dehydrogenation (reduction step), which was attributed to the larger amount of surface-adsorbed oxygen species possessing electrophilic nature and promoting facile deep oxidation reactions. Optimizing the surface iron content, along with the selective formation of thermally stable Ce 0.5 Zr 0.5 O 2 solid solution phases having a larger amount of active lattice oxygen species, was found to be crucial for enhanced catalytic activity and stability in chemical looping-based ODH reactions.