02686nas a2200229   4500008004100000022001400041245011300055210006900168260007300237300001200310490000800322520181200330653002302142653002802165653001902193653002202212653002302234100001802257700002302275700002802298856013002326       2016                        eng d  a0926-337300aSol-gel synthesised WO3 nanoparticles supported on mesoporous silica for liquid phase nitration of aromatics0 aSolgel synthesised WO3 nanoparticles supported on mesoporous sil  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcMAR  a142-1520 v1823 a<p>A series of WO3/SiO2 catalysts have been prepared by sol-gel method using ammonium metatungstate and ethyl silicate-40 (ES-40) as WO3 and SiO2 precursors respectively. The sol-gel method has led to the formation of WO3 nano-particles of 2-5 nm well dispersed on mesoporous silica along with some WO3' agglomerates. Formation of monoclinic WO3 was seen on the catalysts above 5 wt% WO3 loading by XRD analysis. Silica has shown very high surface area of 606 m(2)/g which decreased gradually upto 368 m(2)/g with 20 wt% WO3 loading. 20 wt% WO3/SiO2 catalyst has shown maximum acidity (0.56 mmol NH3/g) with presence of both Lewis and Bronsted acidity. UV-vis DRS analysis showed formation of polytungstate species along with WO3 on silica surface. The prepared catalysts were used for liquid phase nitration of aromatics using 70% nitric acid as nitrating agent without using any sulfuric acid. Very high conversion (99%) was obtained for p-cresol nitration with very high selectivity (99%) for 2-nitro p-cresol. The water formed during the reaction was removed azeotropically using ethylene dichloride as solvent. In case of o-xylene 74% conversion was obtained with 54% selectivity for 4-nitro o-xylene. The effect of different WO3 precursors on nitration efficiency was studied using sodium tungstate and tungstic acid as precursors. However,ammonium metatungstate showed the highest acidity. Sodium tungstate showed formation of dimer of sodium tungstate which did not show any acidity and hence no activity for nitration. The mechanism for nitration using WO3/SiO2 has been proposed based on polarisation of water on tungsten centre generating Bronsted acidity which can further generate nitronium ion giving subsequently nitration of the aromatic ring. (C) 2015 Elsevier B.V. All rights reserved.</p>10aAromatic nitration10aheterogeneous catalysis10aRegioselective10aSol-gel synthesis10aWater polarization1 aKulal, A., B.1 aDongare, Mohan, K.1 aUmbarkar, Shubhangi, B.  uhttps://library.ncl.res.in/content/sol-gel-synthesised-wo3-nanoparticles-supported-mesoporous-silica-liquid-phase-nitration-002487nas a2200253   4500008004100000022001400041245008100055210006900136260000800205300001200213490000800225520170000233653002301933653001301956653002801969653001601997653002202013100001802035700001902053700001902072700002002091700002102111856010102132       2019                        eng d  a0926-860X00aHydrophobic WO3/SiO2 catalyst for the nitration of aromatics in liquid phase0 aHydrophobic WO3SiO2 catalyst for the nitration of aromatics in l  cMAR  a105-1130 v5743 a<p>WO3/SiO2 solid acid catalyst synthesized using sol gel method has shown promising activity (up to 65% conversion) for aromatic nitration in liquid phase using commercial nitric acid (70%) as nitrating agent without using any sulfuric acid. The water formed during the reaction as well as water from dilute nitric acid (70%) was removed azeotropically, however due to the hydrophilic nature of the catalyst, some water gets strongly adsorbed on catalyst surface forming a barrier layer between catalyst and organics. This prevents effective adsorption of substrate on catalyst surface for its subsequent reaction. To improve the activity further, the hydrophilic/hydrophobic nature of the catalyst was altered by post modification by grafting with commercial short chain organosilane (Dynasylan 9896). The modified 20% WO3/SiO2 catalyst when used for o-xylene nitration in liquid phase, showed significant increase in the conversion from 65% to 80% under identical reaction conditions. Catalyst characterization revealed decrease in the surface area of 20% WO3/SiO2 from 356 m(2)/g to 302 m(2)/g after grafting with Dynasylan 9896. The fine dispersion of WO3 particles (2-5 run) on silica support was not affected due to modification. NMR and FTIR study revealed the decrease in surface hydroxyl groups imparting hydrophobicity to the catalyst. Interestingly the total acidic sites of the catalyst remained almost unaltered (0.54 mmol NH3/g) even after modification. Even though, the acidity and other characteristics of the catalyst did not change appreciably, there was a considerable increase in the o-xylene conversion which can be ascribed to the hydrophobic nature of the catalyst.</p>
10aAromatic nitration10agrafting10aheterogeneous catalysis10aHydrophobic10aSol-gel synthesis1 aKulal, A., B.1 aKasabe, M., M.1 aJadhav, P., V.1 aDongare, M., K.1 aUmbarkar, S., B.  uhttps://library.ncl.res.in/content/hydrophobic-wo3sio2-catalyst-nitration-aromatics-liquid-phase