Preparation and characterization of mono-/multi-metallic hydrophobic catalysts for the oxidative esterification of methacrolein to methyl methacrylate

Abstract

The direct oxidative esterification of methacrolein (MAL) with methanol and oxygen to methyl methacrylate (MMA) was carried out over Pb and Bi-doped hydrophobic styrene-divinyl benzene copolymer (SDB) supported Pd catalyst under mild conditions. The Pd–Pb–Bi/SDB catalyst showed higher activity than bimetallic Pd–Pb/SDB and Pd–Bi/SDB, and much higher than monometallic Pd/SDB catalyst and hydrophilic catalysts. The multi-metallic catalysts were prepared through step impregnation method and characterized by N2 adsorption–desorption isotherm, environment scanning electron microscope (ESEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that addition of Pb and Bi to Pd catalyst produced an important decrease in the metallic particle size, and the intermetallic Pd3Pb and PdBi crystals were found in the multi-metallic catalysts, which facilitate the excellent performance of multi-metallic catalyst.