The role of water in silicate oligomerization reaction.

The silicate oligomerization reaction is key to sol-gel chemistry and zeolite synthesis. Numerous experimental and theoretical studies have been devoted to investigating the physical chemistry of silicate oligomers in the prenucleation stage of siliceous zeolite formation. Most of the previous quantum chemical computational work has used gas phase models or continuous solvent models for silica oligomerization. Here we apply Car-Parrinello molecular dynamics simulations with explicit inclusion of water molecules to investigate the reaction pathway for the anionic bond formation of siliceous oligomers. The rates of SiO-Si bond formation of linear or ring containing silicate oligomers become substantially enhanced, compared to gas phase results. The formation of 3-ring oligomer is more favorable than the formation of higher branched and ring silica oligomers.