Home

About

Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network
FAQHELPSITE MAPCONTACT US


  Advanced Search  

 
New Force Field for Na Cations in Faujasite-Type Zeolites Eugenio Jaramillo and Scott M. Auerbach*,,
 

Summary: New Force Field for Na Cations in Faujasite-Type Zeolites
Eugenio Jaramillo and Scott M. Auerbach*,,
Departments of Chemistry and Chemical Engineering, UniVersity of Massachusetts, Amherst,
Amherst, Massachusetts 01003
ReceiVed: April 28, 1999; In Final Form: July 26, 1999
We have developed and validated a new force field for cations in zeolites, which explicitly distinguishes Si
and Al atoms, as well as different types of oxygens in the framework. Our new force field gives excellent
agreement with experimental data on cation positions, site occupancies and vibrational frequencies. Energy
minimizations show that Na cations in site I are not at the centers of hexagonal prisms, but rather are in one
of two symmetric SI sites displaced by about 0.6 along the [111] direction. Molecular dynamics (MD)
simulations show that most cations are immobile in Na-X and Na-Y on the MD time scale, even at 1000
K. Only Na-X cations in site III exhibit diffusive motion at 1000 K, with a self-diffusivity from MD of 3.6
10-10 m2 s-1. The MD simulations also show that cation movement is highly correlated, composed of
jumps involving at least 4 cations or more.
1. Introduction
Cation-containing zeolites have recently been found to be
effective for separating various hydrofluorocarbon (HFC)
mixtures,1 such as HFC-134 (HF2C-CF2H), and HFC-134a
(F3C-CFH2). To develop an understanding of the factors that
control this and other separations, Grey et al.2 reported a

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry