Heteropolyoxometalates which are included in microporous silica, Cs xH 3− xPMo 12O 40/SiO 2 and Cs yH 5− yPMo 10V 2O 40/SiO 2, as insoluble solid bifunctional catalysts: synthesis and selective oxidation of benzyl alcohol in liquid–solid systems

Abstract

Heteropolyoxometalates (HPOMs) which are included in microporous silica, Cs x H 3− x PMo 12O 40/SiO 2 and Cs y H 5− y PMo 10V 2O 40/SiO 2, have been synthesized by a sol–gel technique and characterized by IR, UV–VIS, X-ray and N 2 adsorption isotherms. IR and UV–VIS data indicate that the identities of Cs x H 3− x PMo 12O 40 and Cs y H 5− y PMo 10V 2O 40 are preserved within these synthesized compounds. TEM image and BET adsorption isotherms confirm the presence of nanometer particles and microporous structures. X-ray powder patterns prove that the cesium salts of the HPOMs are uniformly dispersed in the silica network. As insoluble solid bifunctional catalysts, they show high catalytic activity and selectivity for selective oxidation of benzyl alcohol into benzyl aldehyde by H 2O 2 in liquid–solid systems. The highest activity is observed at x=1.5 or y=2.5 in Cs x H 3− x PMo 12O 40/SiO 2 or Cs y H 5− y PMo 10V 2O 40/SiO 2, respectively.