Ceria and its related materials for VOC catalytic combustion: A review

Based on unique oxygen storage capacity (OSC), ceria catalysts are widely investigated for remediation of volatile organic compounds (VOCs) over the recent decade. It is generally accepted that VOC oxidation on ceria is through Mars-van Krevelen mechanism, where lattice oxygen (OLat) reacts with adsorbed VOC molecule, followed by re-oxidation of reduced ceria by replenishing OLat from gaseous O2. Oxygen vacancy and oxygen mobility are the key factors involved that influence the OSC and consequently modify the catalytic performance. Many strategies have been explored in the literature to optimize the materials. For the formation energy of oxygen vacancies varies with crystal orientation, ceria with specific morphologies (i.e., nanorods with (110) and (100)) perform better than the typical ceria catalysts. Beyond that, transition metal cations (e.g., V5+, Zr4+, Cr3+, Mnx+, and Cu2+) can dope or aliovalent substitute into ceria lattice, resulting in more defects and tuning the reactivity. Precious metal nanoparticles (e.g., Au, Pt, Pd, Ru) are known to activate the lattice oxygen at the interface of noble metal and ceria, facilitating the transformation of surface oxygen species and decreasing the light-off temperature. These strategies are also applicable to keep ceria from deactivation when facing chlorinated VOCs (CVOCs) and volatile sulfur compounds (VSCs).