Oxidative degradation of cresol isomers using ozone in the presence of SiO2-supported nickel, iron, manganese and vanadium catalysts

Abstract

We report the catalytic ozonation as a viable tool in the oxidative degradation of cresol isomers. SiO2-supported metal catalysts with 2.5 and 7.5 wt.% (Ni, Fe, Mn, V) were employed in this ozone initiated oxidation reactions. All catalysts were characterized using various analytical techniques such as XRD, FT-IR, SEM-EDX, TEM, ICP-OES, and BET-surface area analyses. XRD studies revealed the existence of Fe as Fe2O3 and Mn as Mn3O4 on the supports’ surface. EDX results displayed a dispersion homogeneity of the metals over the surface of SiO2 support, and the ICP-OES analysis confirm the concentration of a loaded metal. The degradation of cresols (m-, o-, p-cresol) was investigated by aerating each substrate with ozone (0.123 mg/L) in a glass reactor from 6 to 24 h of reaction time at ambient reaction conditions. The catalytic activities of various metal loaded SiO2 catalysts in terms of conversion and selectivity were studied. The reaction products of various cresol isomers were identified using GC–MS analysis. m-Tolyl acetate (m-TA), 2,3-dihydroxytoluene (2,3-DT), diethyl maleate (DM) and diethyl oxalate (DO) were the identified products in the oxidative degradation of m-Cresol. Whereas, o-cresol yielded o-tolyl acetate (o-TA), 2,5-dihydroxytoluene (2,5-DT), DM and DO as products. p-Cresol produced p-tolyl acetate (p-TA), 3,4-dihydroxytoluene (3,4-DT), DM and DO as reaction products. The Ni(2.5%)/SiO2 catalyst possess excellent activity towards the conversion of m-cresol (85.0%), whereas, Fe(2.5%)/SiO2 led to highest conversion for both o-cresol (76.3%) and p-cresol (87.0%).