Aerogel and xerogel WO3/ZrO2 samples for fine chemicals production

Abstract

a b s t r a c t WO 3 /ZrO 2 systems were prepared by sol-gel technique using different procedures for the solvent extraction: evaporation in vacuum at room temperature (xerogel) and extraction in supercritical conditions (aerogel). Two reactions of industrial interest were investigated under mild conditions: (i) acylation of veratrole with acetic anhydride; (ii) acylation of anisole with benzoic anhydride. Several techniques were employed in order to study the influence of the synthetic parameters on texture and catalytic activity: N 2 physisorption, Fourier transformed-infrared spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction and temperature programmed oxidation analyses. The solvent extraction strongly influences metal reducibility, surface area, pores organisation, W/Zr surface density and metallic interactions. The aerogel sample shows the best catalytic results for both conversion and yield. The supercritical extraction plays a central role especially in the recycling: by proper air activation, the aerogel sample attains the complete restoration of the catalytic activity even after three runs.

An alumina‐coated UiO‐66 nanocrystalline solid superacid with high acid density as a catalyst for ethyl levulinate synthesis

“…The isotherm of SO 4 2− /ZrO 2 in Fig. 3(b) contained a hysteresis loop in the P / P 0 range from 0.4 to 0.8, which confirmed the presence of mesopores in the sample 52 . The BET specific surface area of SO 4 2− /ZrO 2 was only 87 m 2 g −1 , and the average pore diameter was 3.2 nm (Table 1).…”

“…3(b) contained a hysteresis loop in the P/P 0 range from 0.4 to 0.8, which confirmed the presence of mesopores in the sample. 52 The BET specific surface area of SO 4 2− /ZrO 2 was only 87 m 2 g −1 , and the average pore diameter was 3.2 nm ( Table 1). The SO 4 2− /ZrO 2 sample was prepared by calcining UiO-66 after impregnation with ammonium sulfate solution.…”

“…The significant hysteresis loop in the range from 0.6 to 0.9 (P/P 0 ) indicated the presence of mesopores. 52 This was a type H 3 hysteresis loop according to the IUPAC classification system, which indicated a cracked pore structure. 53 The adsorption-desorption isotherm showed that SO…”

Effect of the doping agent nature on the characteristic and catalytic properties of aerogel zirconia catalysts doped with sulfate groups or heteropolytungstic acid

“…Such catalysts have been prepared by sol-gel method and dried either in supercritical condition of solvents or in ordinary condition [4][5][6][7][8][9] since sol-gel route offers a better control of the homogeneity of the prepared solids as regards to other methods [10][11][12]. For zirconia based catalysts, the sol-gel method offered the opportunity to introduce in one step zirconium alkoxide, metal precursor and sulfate groups as dopant in order to assure the homogeneity and to control morphological and textural properties of the final materials [13,14].The obtained results showed that aerogels manifest developed textural properties as well as higher acidity.…”

Gallium-Containing Mesoporous Silica: Supported Catalysts with High Catalytic Activity for Oxidation of Benzene, Toluene ando-Xylene

“…This confirms the XRD results, which suggested that the gallium is dispersed on the surface, as metallic gallium and in the oxide form, which may be favorable for complete oxidation to occur on the surface of these materials. 23,24 XPS analysis of the surface of the catalysts was carried out to determine the percentage of Ga 2 O 3 on the surface of the catalysts. Interestingly, the catalyst MS-Ga7% presented a higher amount of Ga 2 O 3 on the surface of the material compared to MS-Ga11%.…”