Oxidative-acidic bifunctional catalyst of niobium-phosphate-titania supported on silica in production of diols

Abstract

Niobium-phosphatetitania supported on silica as oxidative-acidic bifunctional catalyst has been synthesized via sol-gel and impregnation methods in different sequences n"r"]y, (i) TiO2, l\brO, and POa3-impregnated stepwise onto silica (P/Nb/T.i/Si), (ii) mixture of TiO2 and Nb2O5 ffleonateo onto silica, f9]l_owed by impregnation of eoo]1e71Nu+Ti)/Si), ano liiii Nb2o5 and PO+" Impregnated onto TiO2-SiO2 (P/Nb/Ti-Si). The results indicated the diffeient properties resulted from varied jnteractions among SiO2 support, TiO2 catalyst and its modifiers have greatly affected the bifunctional catalytic behavior of the synth-esized materials. The XRD results showed an identified peak of titanium oxide in sample P/Nbffi/Si. Meanwhile, samptes P/(Nb+Ti)/Si and P/Nb/Ti-Si were in amorphous form indicating that Ti and Nb were dispeised well on the surface of silica. UV-Vis DR results revealed that oitaheoral or polymeric Ti species was the dominant species in sample P/Nb/Ti/Si while hydrated tetrahedrri Ti rp""ies was predominant in samples P/(Nb+Ti)/Si and P/Nb/Ti-Si. Besides of tetrahedrallv coordinated Ti species, it has been demonstrated that the presence of Nb, POa3- as well as ifr" SiO, support has contributg_d significantly in improving the oxidative catalytic activity. Meanwhile, interaction between PO4"- groups and Nb has generated Bronsted acidity for the high yield of diol. lt has been shown that P/Nb/Ti-Si was the best bifunctional oxidaiive-acidic 6atilystin consecutive transformation of 1-octene to 1,2-octanediol through formation of 1,2-epoxyoctane using aqueous H2O2at 343 K.lt was expected that synthetic method used in preparation of p/Nb/Ti-Si has aided the effective interaction between POa3- and Nb, leading to foimaiion of more Bronsted acidity in this sample.