Adsorption of linear and branched alkanes in Ferrierite: a computational study

Molecular simulations using the Configurational-bias Monte Carlo technique were performed to calculate the adsorption behavior of linear and branched alkanes (carbon numbers ranging from 4 to 6), and their 50%-50% mixtures on Ferrierite. It was found that small molecules (up to C4 backbone) can occupy both channels of Ferrierite while larger molecules (from C6 backbone) can only reside in the 10-ring channels of Ferrierite. As a consequence, the isotherms of n-pentane and 2-methylpentane exhibit inflection points. The probability distribution of branched alkanes along the 10-ring channel was found to be discontinuous, while this distribution is continuous for linear molecules. This is confirmed by the calculation of free energy profiles in the zeolite. The possible consequences for the diffusion mechanism and catalysis are briefly discussed. It was found that mixture isotherms can be rationalised on the basis of the pure component isotherms