Precipitated silica

About: Precipitated silica is a research topic. Over the lifetime, 1401 publications have been published within this topic receiving 20992 citations.

Process for the preparation of precipitated silica, precipitated silicas thus obtained, and their use in the reinforcement of rubbers

Abstract: A process for the preparation of precipitated silica having an aptitude for dispersion and improved reinforcing properties. The invention also relates to new silicas which exist in the form of granules, powder or substantially spherical balls, these silicas being characterised in that they have both a BET specific surface and a CTAB specific surface of between 140 and 200 m /g, and in that the porous volume constituted by the pores with diameters between 175 ANGSTROM and 275 ANGSTROM represents at least 50 % in the case of powders and balls, and at least 60 % in the case of granules, of the porous volume constituted by the pores with diameters less than or equal to 400 ANGSTROM . Additionally, the granules have a degree of attrition which is less than 20 %, the powder which is a DOP oil uptake of between 180 and 350 ml/100 g, and the balls a mean size of at least 80 mu m. The invention also relates to the use of the said silicas as reinforcing fillers for plastics (elastomers).

Comparison of liquid-phase olefin epoxidation over MoOx inserted within mesoporous silica (MCM-41, SBA-15) and grafted onto silica

Abstract: Molybdenum(VI)-containing siliceous-MCM-41 and -SBA-15 mesoporous molecular sieves and silica-supported molybdenum(VI) complexes have been prepared according to an original pathway by the reaction between low-cost Mo(VI) peroxo species and silica precursors (tetraethylorthosilicate), silica beads (pure SiO2) or precipitated silica in an acidic and peroxidic medium (peroxo route). Hydrogen peroxide is added to avoid the formation of iso-(or hetero-)polyoxometalates in the direct one-pot synthesis of mesoporous solids, or in the case of pure SiO2. The resulting calcined materials have been characterized by chemical analysis, X-ray powder diffraction, nitrogen sorption isotherms, TEM and EDX analysis, UV–vis diffuse reflectance spectroscopy, Raman spectrometry and catalysis tests. The peroxo routes lead to inserted and/or supported molybdenum oxide zones which are restricted in size due to the porous structure of the silica-based materials and to the involment of low-condensed and even mononuclear oxoperoxo species. This allows to support MoOx species in a dispersion which cannot be achieved with the systems using heptamolybdate [Mo7O24]6− salts or heteropolyoxometalates, which favor the anchoring of MoO3 clusters. Catalysis tests show that the very dispersive structure of the MoOx-siliceous-MCM-41, -SBA-15 and MoOx/SiO2 promotes the generation of fairly active oxidation catalysts for liquid-phase olefin epoxidation (cyclooctene, R-(+)-limonene from ambient to 40 °C) using anhydrous tert-butylhydroperoxide (TBHP) as oxidant. Under specific conditions, leaching of redox-active species has been minimized (less than 2 ppm) especially with MoOx/SiO2 which is proposed as the simplest catalyst for these oxidations. MCM-41 and SBA-15 do not show clear advantages over silica in epoxidation reactions with TBHP.