Pd–Pb/SDB Bimetallic Catalysts for The Direct Oxidative Esterification of Methacrolein to Methyl Methacrylate

Pd–Pb/SDB catalyst prepared by depositing lead and palladium on hydrophobic styrene-divinylbenzene (SDB) copolymer constitutes a new and highly efficient catalyst for the oxidative esterification of methacrolein with methanol to methyl methacrylate under mild conditions. Compared to the monometallic Pd/SDB catalyst and conventional hydrophilic catalysts supported on γ-Al2O3, the Pd–Pb/SDB bimetallic catalyst shows higher reaction rate and product selectivity. The Pd–Pb/SDB catalyst was prepared by impregnating method and characterized by N2 adsorption–desorption isotherm, X-ray diffraction (XRD), environmental scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that Pd–Pb atoms formed intermetallic Pd3Pb1 crystals and the active component had a better dispersion and a smaller particle size than Pd/SDB. The SDB-supported catalyst could be recycled easily and reused, even up to seven cycles, without any appreciable loss efficiency. Based on the experimental results, the potential reaction mechanism was also proposed.