Insight into regioselective hydrogenation of methyl phenyl glyoxalate to methyl mandelate over Pt/α-MnO₂ nanorods

Abstract

MnO₂ as a material possesses several applications in environmental chemistry, electrochemistry, adsorption chemistry, heterogeneous catalysis, etc. In this work different polymorphs of MnO₂(α, β, γ and δ) were synthesized by hydrothermal synthesis and their compatibility as a support for hydrogenation of methyl phenyl glyoxalate to methyl mandelate was studied. These polymorphs appeared in different shapes like nanorods, nanofibers, spines and urchin like. All catalysts were defined and characterised using different technique such as DSC-TGA, FTIR, SEM, TEM, XRD, TPD, TPR and BET. The activity of all catalysts was tested for regioselective liquid phase hydrogenation of methyl phenyl glyoxalate (MPG). Among all catalysts α-MnO₂ (cryptomalene phase) was the best support for loading platinum metal. Different Pt loadings were studied, i.e. 1 %, 2.5 % and 5 % (w/w). 1 % platinum loading was found to be optimum. The catalyst was active, selective and reusable. A plausible reaction mechanism is presented and kinetic model developed. The activation energy was found 19.7 kcal/mol.