Novel oxidative-acidic bifunctional catalyst of tungsten-phosphate modified silica-titania

Abstract

In this work, methyl ß-cyclodextrin (Mß-CD) was used to increase the solubility of turmeric rhizome oleoresin (TRO) in aqueous solution by forming inclusion complexes, and the technique was combined with microwave-assisted extraction (MAE) to extract the curcuminoids from Curcuma domestica Val. Optimized conditions for the MAE were microwave power of 700 W, extraction particle size of 0.30–0.60 mm, extraction time of 3 min, solvent volume of 10 mL, 2 g of sample, and extraction temperature of 60 °C. High-performance liquid chromatography was used for the determination of the curcuminoids. Phase solubility study was conducted to investigate the association of Mß-CD with TRO using curcumin, the major curcuminoid, as a marker compound to represent turmeric oleoresin. The curcumin recovery was increased due to its complexation with Mß-CD. Linear host–guest correlation with slope of <1 indicated a stoichiometry of 1:1 Mß-CD-complex, and with this assumption, the stability constant, KC, was calculated as 515.19 M-1. Meanwhile, the molar ratio needed for inclusion complexation between TRO/Mß-CD was 1:2. Attenuated total reflectance Fourier transform infrared spectroscopy results revealed that the MAE application for the co-precipitation, physical, and kneading methods can all be used for complexation.A novel oxidative-acidic bifunctional catalyst of silica-titania supported tungsten-phosphate was successfully synthesized and characterized. Different tungsten amount was impregnated into silica-titania followed by phosphoric acid treatment via sol gel method. The impregnation of WO3 and PO43- into TiO2-SiO2 followed by drying and calcination gave the white colour to the samples. X-ray diffractograms of the samples showed the structures of TiO2-SiO2 remained as amorphous structure after loading of WO3 and PO43-. The catalytic performance of the samples of PO43-/xW/TiO2-SiO2, (x = 1 and 5 wt %) as bifunctional catalyst in the formation of 1,2-octanediol through conversion of 1-octene to 1,2-epoxyoctane using aqueous H2O2 as an oxidant was evaluated. It has been demonstrated that PO43-/5W/TiO2-SiO2 was an active bifunctional oxidative-acidic catalyst in producing 1,2-octanediol from 1-octene.