Effect of Counter Ions on the Silica Oligomerization Reaction

✍ Scribed by Thuat T. Trinh; Antonius P. J. Jansen; Rutger A. van Santen; Joost VandeVondele; Evert Jan Meijer

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 428 KB
• Volume: 10
• Category: Article
• ISSN: 1439-4235
• DOI: 10.1002/cphc.200900006

✦ Synopsis

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.