Synthesis and catalytic activity of chrysotile-type magnesium silicate nanotubes using various silicate sources

• Published in: Microporous and mesoporous materials Vol. 274; pp. 176 - 182
• Main Authors: López-Salinas, E., Toledo-Antonio, J.A., Manríquez, M.E., Sánchez-Cantú, M., Cruz Ramos, I., Hernández-Cortez, J.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15-01-2019
• Subjects: Aldol-condensation; Chrysotile; Nanotubes; TEM; XRD; Chrysotile; XRD; Aldol-condensation; TEM; Nanotubes
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2018.07.041

Chrysotile-type Mg3Si2O5·(OH)4 nanotubes (MgSi-NTs) were obtained (by a hydrothermal method) using different SiO2 sources. Sources of silica, as raw material, were varied from sodium silicate (typical preparation) to colloidal silica of 12–22 nm colloid size. Around 13 g of MgSi-NTs were prepared by using 7.8 L Teflon-lined autoclave at 240 °C. In all synthesis attempts, XRD was used to identify chrysotile crystal phases, which were later confirmed by TEM, showing bundles of hollow cylindrical particles of MgSi-nanotubes from 60 to 218 nm length and internal diameters from 5 to 8 nm. Specific surface areas obtained by nitrogen adsorption of MgSi-NTs samples (annealed at 600 °C) were between 105 and 202 m2/g with average pore diameter from 7 to 32 nm, depending on silica precursor. Thermal stability of MgSi-NTs was examined by TGA-DTA, XRD and TEM. From TEM images, it was clear that nanotubes from colloidal silicas can hold up below 600 °C. Sodium silicate obtained nanotubes were less thermally stable (below 500 °C), though. The use of colloidal silica, instead of sodium silicate, upgraded specific surface area and pore volume values of resulting MgSi-NTs. Number of basic sites and properties were measured by CO2-TPD ranging between 66 and 89 μmol CO2/g cat, and their catalytic activity was assessed on aldol condensation of acetone reaction at 300–350 °C, where the main products obtained were mesityl oxide and isophorone, which are valuable products for fine-chemistry industry.
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•Nanotubes of magnesium silicates were synthesized.•Scale up of nanotubes to decagram amount was achieved by hydrothermal route.•Nanotubes are thermally stable at ≤600°c.•Various colloidal Silica sources were used in the synthesis.•Magnesium silicates nanotubes catalyze aldol condensation of Acetone.