Synthesis supercritical drying

Solgel processing specifies a type of solid material synthesis method performed in a liquid and at low temperatures [152], The produced inorganic solids, mostly oxides or hydroxides, are formed by chemical transformation of chemical solutes termed precursors. The solid is formed as the result of a polymerization process that involves the establishment of M-OH-M or M-O-M bridges between the metallic atoms M of the precursor molecules [152], The drying process, after the gel formation, is carried out at a relatively low temperature to produce a xerogel, or by a supercritical drying process. 

In each case, a pure and its corresponding doped oxide were prepared with a weight content of yttria of 8 %, the volumetric ratio of precursor to solvent was 1/1, and the supercritical drying temperature was 265 °C while a stoichiometric quantity of water was reacted for the hydrolysis reactions. All reactants were vigorously stirred at ambient temperature to carry out the sol-gel achievement. Table 1 gives the precursors and corresponding solvent of the synthesis. No catalyst was added to the reactant mixtures. 

Sol-gel synthesis conditions, supercritical drying conditions, catalytic activity in bcnzylation of benzene, surface area and overall pore volumes of xerogcl and aerogel catalyst are shown in Table 3. 

More recently. Ye et al. proposed a new sol—gel method combined with a supercritical drying technique for the synthesis of nanocomposite electrocatalysts for ORR. They claimed that their method had a structure-preserving ability and favored a nanoscale mixing of the constituents, and then could produce a remarkably homogeneous solution. The chemical, physical, and morphological properties of catalysts produced using this sol—gel... 

Silica and, to a less extent, alumina aerogels are detailed below because most of the catalytic aerogels are silica- or alumina-based composites. As mentioned in the Abstract section, the synthesis of an aerogel results from a two-step process First, a solution-to-sol-to-gel is prepared, and second, this gel is supercritically dried in an autoclave. 

Suh D J, Park T J (2002) Synthesis of high-surface-area zirconia aerogels with a well-developed mesoporous texture using CO2 supercritical drying. Chem Mater 14 1452-1954... 

Bedilo A F, Klabunde K J (1997) Synthesis of high surface area zirconia aerogels using high temperature supercritical drying. J Nano Mater 8 119-135... 

Tyagi B, Sidhpuria K, Shaik B, Jasra R V (2006) Synthesis and characterization of nanocrystalline mesoporous zirconia using supercritical drying. J Nano Nanotech 6 1584-1593... 

The silica aerogel investigated was a one-step base-catalyzed supercritically dried silica gel (TMOS). For details of the synthesis see e.g. references [5,6]. To increase the stiffiiess of the as-prepared sample and thus to avoid a significant volume change due to capillary forces [2] we sintered the silica aerogel to a density of about 0.29 g/cm (initial density 0.26 g/cm ). 

---