Mn Supported on Ce Substituted Hydroxyapatite for VOC Oxidation: Catalytic Activity and Calcination Effect

Abstract

The Mn supported on Ce substituted hydroxyapatite (HAp) catalyst was prepared by co-precipitation method and investigated for the low-temperature oxidation of toluene as a model component of VOC. The present work demonstrated the substitution of Ce in HAp in place of Ca. Furthermore, the effect of calcination temperature on oxidation activity of the catalyst was examined by calcining the catalyst at 400, 500 and 600 °C. The low-temperature calcination could favour the insertion of Ce in HAp, whereas higher calcination temperature could lead to the formation of separate CeO₂ phase. The catalyst was characterized by using XRD, surface area, XPS, H₂-TPR, ATR-FTIR techniques. The probable bonding between Ce and hexagonal HAp, which favors the oxidation of toluene at lower temperature has been explained with the calcination effect. The Ce substitution in HAp leads to the decrease in toluene activation energy which consequently increases the toluene conversion rate. The improvement in Mn₂O₃/Mn₃O₄ ↔ MnO₂ redox cycle was observed due to the Ce substitution compared to unsubstituted Mn supported on HAp. The ATR-FTIR toluene adsorption study demonstrated the plausible mechanism of toluene oxidation. The activation of toluene on Ce substituted catalyst surface could proceed through the adsorption of the –CH₃ group, whereas toluene adsorbed on unsubstituted catalyst surface through ortho, meta or para C–H bond.

Graphic Abstract