One-pot synthesis of Ag-H3PW12O40-LiCoO2 composites for thermal oxidation of airborne benzene

The lithium cobalt oxide (LiCoO2), one of the complex metal oxides that compose the spent Li-ion battery cathodes, was studied for controlling air pollution. The LiCoO2 was modified with AgNO3 and phosphotungstic acid (HPW) via a facile one-pot synthesis to obtain the AgHPWLiCo catalyst, which was comparatively studied with HPWLiCo, AgLiCo and LiCoO2 catalysts by XRD, ATR, H-2 pulse chemisorption, SEM, TEM, XPS, EPR, C6H6-TPD, H-2-TPR and O-2-TPD. The Ag dispersion of the AgHPWLiCo sample was almost ten times that of the AgLiCo catalyst and the addition of Ag could alleviate particle agglomeration. The Ag+ species, the dominant form of Ag, played an imperative role in increasing the benzene adsorption capacity, and both Ag and HPW additions strengthened the interaction of benzene with catalyst surface. Compared with the pristine LiCoO2, the Ag+ species enhanced the reducibility of surface adsorbed oxygen and lattice oxygen, and the HPW addition increased the mobility of lattice oxygen. Due to the synergy between Ag and HPW, the AgHPWLiCo catalyst exhibited a high activity for benzene oxidation: under the reaction conditions of 120 L.g(-1).h(-1) of space velocity, 450-480 ppm of benzene and 300 degrees C, similar to 95% of benzene conversion was achieved over the AgHPWLiCo catalyst whereas only similar to 62%, similar to 45% and similar to 11% of benzene could be removed respectively over the HPWLiCo, AgLiCo and LiCoO2 catalysts. Adding HPW could suppress the build-up of oxidation products on catalyst surface, which might also contribute to the excellent benzene oxidation performance of the AgHPWLiCo catalyst. Besides, the effects of water vapor and SO2 on catalyst activity were investigated.