My research focus is aimed at developing
a simulation protocol to study the effect of confinement in nanoporous
media to chemical reaction kinetics. Chemical reactions within nanoporous
media, such as carbon nanotubes, activated carbon fibers, carbon-slit pores,
mesoporous silica, zeolites, etc., are significantly affected by confinement.
In such reaction media, catalytic effects can occur due to a number of
effects: finite size and reduced dimensionality of the confined phase;
densification and selective adsorption of activated species on the pore
surfaces; pore surface roughness and connectivity, etc. Consequently, the
reaction yield, dynamics, energetics and mechanism are likely to be affected
and be much different from that of the bulk phase, and will vary with pore
size and shape, material and nature of the pore surfaces.
There are in general two different approaches
that we utilize to estimate theoretically the reaction rates for chemical
reactions occurring within nanoporous media. In the first, one starts
with optimization of the structure and construction of the potential energy
surface (PES) for the reaction under study using a suitable ab initio
method followed by semi-classical simulations in either
the Blue Moon ensemble or the transition path ensemble to obtain the kinetic
constants. Possible ab initio methods include the Hartree-Fock(H-F)
method, variational and perturbation methods, such as the various configuration
interaction (CI) methods, the Møller-Plesset (MP) methods, coupled-cluster
methods, etc., and density functional theory (DFT).
An advantage of this approach is that, once the PES is known, the simulation
can be done efficiently and larger systems can be handled. On the other
hand, this approach often involves some human intervention in deciding
on the relevant reaction coordinates, what are the relevant effects that
have to be included in the PES functional form, etc.
The second approach is to embed the
ab initio calculations for the potential energy within a
molecular simulation algorithm, as is done in the ab initio molecular
dynamics (MD) methods, examples of which are the Car-Parrinello MD method
and the Born-Oppenheimer MD method. The main drawback of these methods
is their large computational cost, which has typically limited their applicability
to small systems and time spans.
Our current efforts are towards studying
the reaction equilibrium and kinetics of the water-gas reaction(WGR),
CO +H2OÛ CO2+H2
, occurring within different nanoporous materials. We are currently performing
ab initio calculations to determine the effect of nano-confinement
to the reaction path and transition state structure of the WGR.
Kostov, E.S. Hernandez, and M.W. Cole, “Bound state of dimers on a spherical
surface”, J. Low Temp. Phys. 134, 321 (2004).
Kostov, M.M. Calbi, and M.W. Cole, “Phonons and specific heat of neon
and methane on the surface of a nanotube bundle .” , Phys. Rev.
B 68, 245403 (2003).
Kostov, M.W. Cole, G.D. Mahan, C. Carraro, M.L. Glasser, “Enhanced cohesion
of matter on a cylindrical surface”, Phys. Rev. B 67, 075403
Trasca, M.K. Kostov, M.W. Cole , “Isotopic and spin selectivity of H2
adsorbed in bundles of carbon nanotubes” , Phys. Rev. B 67, 035410 (2003).
Kostov, H. Cheng, A.C. Cooper and G.P. Pez, “The influence of carbon curvature
on molecular adsorptions in carbon- based materials: a force field approach”,
Phys. Rev. Lett. 89 , 146105 (2002).
Williams, B.K. Pradhan, P.C. Eklund, M.K. Kostov and M.W. Cole, “Raman
spectroscopic investigation of H2 , HD , and D2 physisorption
on ropes of single-walled carbon nanotubes”, Phys. Rev. Lett. 88
, 165502 (2002).
Kostov, M.W. Cole and G. Mahan, “Variational approach to the Coulomb problem
on a cylinder”, Phys. Rev. B 66 , 075407 (2002).
Kostov, H. Cheng, R. M. Herman, M. W. Cole, and J. C. Lewis, “Hindered
rotation of H2 adsorbed interstitially in nanotube bundles”, J. Chem.
Phys. 116 (4 ) , 1720-1724 (2002).
Narehood, M.K. Kostov, P.C. Eklund, M.W. Cole, and P.E. Sokol, “Deep inelastic
neutron scattering of H2 in single- walled carbon nanotubes” , Phys. Rev.
B 65 , 233401 (2002).
Kostov, J.C. Lewis, and M.W. Cole, “Gas condensation within bundle of
carbon nanotubes - effects of screening”, in Condensed Matter Theories,
Vol. 16, edited by
S. Hernandez and J. Clark, Nova Science Publishers, New York, 2001;
pp. 161, http://xxx.lanl.gov/abs/cond-mat/0010015 .
Kostov, M.W. Cole, J.C. Lewis, P. Diep, J.K. Johnson, “Many-body interactions
among adsorbed atoms and molecules within carbon nanotubes and in
free space”, Chem. Phys. Lett. 332, 26-34 (2000).
North Carolina State University
Department of Chemical Engineering
113 Riddick Labs
Raleigh, NC 27695
Phone: (919) 513-2051
Fax: (919) 513-2470
Send e-mail to: email@example.com