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

MoO 4 2− -H 2 O 2 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 Na 2 MoO 4 , 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 H 2 O 2 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 H 2 O 2 decomposition experiments support that the alkaline CS carrier can induce the reaction of CMS with H 2 O 2 to preferentially generate the mono-/di-peroxomolybdates as the key species for the selective oxidation of para -alkyl-phenols. Graphical Abstract