Hydrated Calcium Silicate Supported CaMoO₄ as an Efficient and Recyclable Catalyst for Selective Oxidation of Para-Alkylphenols with Hydrogen Peroxide

MoO42--H2O2 is an efficient oxidation system for the conversion of para-alkyl-phenols to high value-added para-peroxyquinols and para-quinols, but its large-scale application is still limited to difficulty in catalyst recovery. This paper discloses that a hydrated calcium silicate (CS)-supported calcium molybdate (CM) catalyst (CMS) is easily fabricated in high-yield and large-scale by simple coprecipitation. Compared to the unsupported CM and Na2MoO4, CMS has an enhanced catalytic activity for the selective oxidation of para-alkyl-phenols, but also it shows a drastically improved selectivity for the target products, which can achieve 84% conversion and 100% selectivity for the goal products in catalyzing the oxidation of 2,4-xylenol with -H2O2 in water. Also, it is very efficient for the selective oxidation of other p-alkyl substituted phenols in water or methanol, especially including the highly selective oxidation of p-cresol which is easy to be overoxidized. More importantly, the CMS catalytic system can be conveniently recovered and repeatedly run without significant activity loss, showing a good reusability. In situ UV-DRS and FT-IR spectra, as well as H2O2 decomposition experiments support that the alkaline CS carrier can induce the reaction of CMS with H2O2 to preferentially generate the mono-/di-peroxomolybdates as the key species for the selective oxidation of para-alkyl-phenols. [Graphics] .