title: Effect of counter ions on the silica oligomerization reaction.
abstract: The silicate oligomerization reaction is key to sol-gel chemistry and zeolite synthesis. Numerous experimental and theoretical studies have addressed the physical chemistry of silicate oligomers in the prenucleation stage of siliceous zeolite formation. Here we report a study of a silica condensation reaction in aqueous solution in the presence of counter ions (Li(+) and NH(4)(+)). Ab-initio molecular dynamics simulations have been used to construct reaction energy diagrams including transition state free energies. Contact with Li+ as well as NH(4)(+) increases the activation energies of the dimerization step compared to the situation in the absence of counterions. The presence of NH(4)(+) has no effect on consecutive oligomerization steps. Hence NH(4)(+) will increase the relative formation rate of larger oligomers.
authors.affiliation: Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Thuat T
authors.initials: TT
authors.lastname: Trinh
authors.forename: Antonius P J
authors.initials: AP
authors.lastname: Jansen
authors.forename: Rutger A
authors.initials: RA
authors.lastname: van Santen
authors.forename: Joost
authors.initials: J
authors.lastname: VandeVondele
authors.forename: Evert Jan
authors.initials: EJ
authors.lastname: Meijer