Highly reactive bulk lattice oxygen exposed by simple water treatment of LiCoO2 for catalytic oxidation of airborne benzene

Abstract

Aiming at a simple and effective way to activate the recycled cathode materials from spent Li-ion batteries for air cleaning, LiCoO2 was synthesized and treated by water for airborne benzene removal. Compared with the pristine sample, whose benzene conversion was ∼20 % at 400 °C, the water-treated one could fulfill 100 % of conversion for 431 ppm of benzene at 300 °C under 120 L g−1 h−1 of space velocity. Furthermore, the water treatment process also worked effectively with the commercialized LiCoO2. Characterization results showed that surface oxygen, i.e., chemically adsorbed oxygen and surficial lattice oxygen, only acted as benzene adsorption sites inert towards benzene oxidation whereas bulk lattice oxygen was reactive for oxidation reaction. Water treatment played two roles in updating the LiCoO2 surface properties. One was to remove the excessive Li2CO3 and the thus-generated sites could adsorb gaseous oxygen, which was catalyzed to directly oxidize the gas-phase benzene into surface by-products at low temperatures (150−200 °C) following the Elay-Rideal pathway. Another more important role was to expose the bulk lattice oxygen by eliminating the surface oxygen species. The thus-exposed bulk lattice oxygen worked at high temperatures (250−400 °C) and could effectively oxidize the adsorbed benzene following the Mars-van Krevelen mechanism.