R. Vanslooten et al., COMPUTER-SIMULATIONS OF THE HIGH-TEMPERATURE ADSORPTION OF METHANE INA SULFIDED GRAPHITE MICROPORE, Langmuir, 10(2), 1994, pp. 542-548
Computer simulations of the adsorption isotherms and energies for meth
ane at 300 K in slit pores are reported. The walls of these pores were
made to be chemically heterogeneous by introducing sulfur atoms into
graphite basal planes. Adsorption in the slit pores with pure graphite
walls has been simulated previously. Modifications in the adsorptive
behavior produced by the substitution of sulfides for some carbon atom
s in the surface planes are shown here. The sulfides form regular latt
ices, with two levels of substitution studied. In the first case, one
carbon atom in fourteen is replaced by sulfur, and in the second, one
atom in eight has been replaced by sulfur. The choices of interaction
potentials for the systems give rise to a very well defined heterogene
ity in the sulfided surfaces. Both the isotherms and the heats show th
at adsorption is enhanced by the introduction of sulfur. However, a de
tailed inspection of the interaction potentials indicates that the ''s
trong sites' for adsorption are not on the sulfides but on the remaini
ng exposed graphite surface between the sulfurs. Distributions of the
adsorption energies of the adsorbed atoms have been evaluated. These d
istributions show that, for such a high temperature, adsorption does n
ot occur by occupation first of the strong sites followed by coverage
of the weaker parts of the surface. Instead, the distributions are ess
entially invariant for coverages up to a large fraction of the monolay
er.