Syntheses of new peroxo-polyoxometalates intercalated layered double hydroxides for propene epoxidation by molecular oxygen in methanol

A new type of layered double hydroxides intercalated by peroxo-polyoxometalates was synthesized by treating PdMAl-[PW11O39] (M = Mg2+ or Zn2+) with 30% H2O2. XRD, FT-IR, and 31P MAS NMR revealed that the interlayer anion [PW11O39]7− was converted mainly to {PO4[WO(O2)2]4}3− and [W2O3(O2)4(H2O)2]2−. 27Al MAS NMR revealed that the brucite-like layers did not collapse during synthesis. PdMgAl-[PW4 + W2] showed 91.5% selectivity for propene oxide at 47.5% conversion during propene epoxidation by O2 in methanol at 353 K for 10 h. The catalytic ability of PdMgAl-[PW4 + W2] can be attributed to the presence of highly active Pd particles in the brucite-like layers that generate H2O2 in situ, the strong epoxidation ability of interlayer peroxo-polyoxometalates with dilute H2O2, and the promotion effect of the basic MgAl-type brucite-like layers toward alkene epoxidation. Moreover, PdMgAl-[PW4 + W2] can be separated and reused by filtration without leaching active components into the solvent.