MOLECULAR-DYNAMICS SIMULATIONS OF ADSORBED ALKANES IN SILICA MICROPORES AT LOW-TO-MODERATE LOADINGS

The configurational and dynamical properties of rigid and flexible alk anes adsorbed on microporous silica are investigated using molecular s imulation techniques. Two isomeric alkanes, neopentane and n-pentane, are examined in detail over a range of surface coverages and temperatu res using the RATTLE simulation algorithm in which the tetrahedrally r igid neopentane and linearly flexible n-pentane molecules are consider ed to be composed of C (neopentane), CH2, and CH3 Lennard-Jones sites. The solid adsorbent is atomistically modelled as a rigid medium using a technique which was shown in earlier work to provide a quantitative ly realistic representation of microporous silica. The simulation resu lts reveal the significant influence of intramolecular structure and d ynamics on the properties of the adsorbed molecules. In particular, on e of the features observed in the n-pentane simulations, which may hav e a direct bearing on the catalytic activity of silica, is a substanti al broadening in the bond angle and dihedral angle distributions durin g adsorption onto the heterogeneous silica surface.