2019, №4

сс. 49-62

Structuring and Phase Formation in Silica Gel in Water Fluids of Different Densities

2019, №4

сс. 49-62

Цитировать

E.A. Lagunova, Yu.D. Ivakin, M.Yu. Sinev, D.P. Shashkin, Z.T. Fattakhova, Yu.A. Gordienko

Key words: water fluid, density, silica, morphology, structuring, crystallization, catalyst support, oxidative coupling of methane

The effect of the density of water fluid in the range of ~10-3—0.25 g/cm3 on the
structuring of amorphous silica gel was studied at 380 °C that exceeds the temperature
of critical point of water. It is shown that a decrease in the specific surface area (Ssp) is
already observed at the lowest density; as the latter increases, Ssp decreases further,
and starting from a density of ~0.01 g/cm3, the formation of crystalline silica phases
(cristobalite, keatit) is observed in the sample. Based on the observed regularities in
the change in the morphology and crystallinity of SiO2, as well as the analysis of data on
the variations in the properties of the water fluid with temperature and pressure
below and above the critical point, it was concluded that the increase in the structuring
rate with an increase in the density of the aqueous fluid is more likely due to the
kinetic factor (mass action law) than with a change in the physical state of water
(intermolecular interaction forces action). Using the obtained samples of treated silica
gel as a support for the NaWMn/SiO2 catalyst for the oxidative coupling of methane
it was shown that the efficiency of the catalyst decreases with increasing degree of
crystallinity of the support. However, when using supports that have undergone processing
at relatively low densities of water fluid (< 0.05 g/cm3), the catalysts are more active
and selective than the one supported on the initial silica gel.

doi:10.1134/S199079312007009X