Heteropoly Acid Supported on Cu-Doped Three-Dimensionally Ordered Macroporous SiO2 as Efficient Catalyst for the Selective Oxidation of Methacrolein

Cu-doped three-dimensionally ordered macroporous (3DOM) SiO2 was prepared by a colloidal templating method and used as the support of heteropoly acid for the selective oxidation of methacrolein (MAL) to methacrylic acid (MAA). The doping effects of Cu on the structures, physico-chemical properties and catalytic performances of the catalysts were investigated. Results showed that Cu was well distributed in the SiO2 framework with the mole ratio of Cu/Si = 5%, and the specific surface area was much higher than that of the pure 3DOM SiO2. After supported with H4PMo11VO40 (HPVA), the specific surface areas of the as-synthesized catalysts significantly decreased, from 239 to 64 m2 g−1 for HPVA/3DOM (5%Cu)–SiO2 and from 141 to 32 m2 g−1 for HPVA/3DOM SiO2, respectively, because of the blockage of the micropores. The supported HPVA retained Keggin-type primary structure and its reducibility was obviously improved due to the existence of Cu in the supports, which thereby resulted in the great enhancement of the catalytic property. The conversion of MAL and the selectivity to MAA were respectively 36 and 47% on HPVA/3DOM SiO2. Comparatively, the conversion of MAL reached 63% with 82% MAA selectivity on HPVA/3DOM (5%Cu)–SiO2.