The initial step of silicate versus aluminosilicate formation in zeolite synthesis: a reaction mechanism in water with a tetrapropylammonium template
Permanent link to this recordhttp://hdl.handle.net/10754/599925
MetadataShow full item record
AbstractThe initial step for silicate and aluminosilicate condensation is studied in water in the presence of a realistic tetrapropylammonium template under basic conditions. The model corresponds to the synthesis conditions of ZSM5. The free energy profile for the dimer formation ((OH) 3Si-O-Si-(OH) 2O - or [(OH) 3Al-O-Si-(OH) 3] -) is calculated with ab initio molecular dynamics and thermodynamic integration. The Si-O-Si dimer formation occurs in a two-step manner with an overall free energy barrier of 75 kJ mol -1. The first step is associated with the Si-O bond formation and results in an intermediate with a five-coordinated Si, and the second one concerns the removal of the water molecule. The template is displaced away from the Si centres upon dimer formation, and a shell of water molecules is inserted between the silicate and the template. The main effect of the template is to slow down the backward hydrolysis reaction with respect to the condensation one. The Al-O-Si dimer formation first requires the formation of a metastable precursor state by proton transfer from Si(OH) 4 to Al(OH) 4 - mediated by a solvent molecule. It then proceeds through a single step with an overall barrier of 70 kJ mol -1. The model with water molecules explicitly included is then compared to a simple calculation using an implicit continuum model for the solvent. The results underline the importance of an explicit and dynamical treatment of the water solvent, which plays a key role in assisting the reaction. © the Owner Societies 2012.
CitationTrinh TT, Rozanska X, Delbecq F, Sautet P (2012) The initial step of silicate versus aluminosilicate formation in zeolite synthesis: a reaction mechanism in water with a tetrapropylammonium template. Physical Chemistry Chemical Physics 14: 3369. Available: http://dx.doi.org/10.1039/c2cp23370c.
SponsorsThis work was funded by King Abdullah University of Science and Technology (KAUST), within the framework of the Special Academic Partnership Program (CADENCED UK-C0017). The computational issue was supported by KAUST Supercomputing Laboratory (Shaheen supercomputer: project k25) and Pole Scientifique de Modelisation Numerique (PSMN) at Ecole Normale Superieure de Lyon. The authors also want to thank Dr Paul Fleurat-Lessard (ENS-Lyon) for fruitful discussions.
PublisherRoyal Society of Chemistry (RSC)
CollectionsPublications Acknowledging KAUST Support
- The mechanism of the initial step of germanosilicate formation in solution: a first-principles molecular dynamics study.
- Authors: Trinh TT, Rozanska X, Delbecq F, Tuel A, Sautet P
- Issue date: 2016 Jun 7
- Zeolite synthesis from paper sludge ash at low temperature (90 degrees C) with addition of diatomite.
- Authors: Wajima T, Haga M, Kuzawa K, Ishimoto H, Tamada O, Ito K, Nishiyama T, Downs RT, Rakovan JF
- Issue date: 2006 May 20
- Silicate glass and mineral dissolution: calculated reaction paths and activation energies for hydrolysis of a q3 si by H3O+ using ab initio methods.
- Authors: Criscenti LJ, Kubicki JD, Brantley SL
- Issue date: 2006 Jan 12
- The role of water in silicate oligomerization reaction.
- Authors: Trinh TT, Jansen AP, van Santen RA, Jan Meijer E
- Issue date: 2009 Jul 7
- Synthesis of zeolites from paper sludge ash and their ability to simultaneously remove NH4+ and PO43-.
- Authors: Wajima T, Shimizu T, Ikegami Y
- Issue date: 2007 Feb 15