Light alkane interactions on transition metal oxides like zirconia using a combined frequency response and DRIFTS study

The frequency response (FR) technique is a powerful method for investigating mass transport in porous materials. Although it is well established in the field of microporous solids, FR is rarely used in the context of mesopores. This study aims to contribute to further exploring this particular field. To this end, sulfated zirconia with ethane, propane, iso-butane, <i>n</i>-butane, and neopentane as adsorptives was selected. While DRIFT spectroscopy is used to investigate the interaction of alkanes with sulfate groups of zirconia, the frequency response method is applied to draw conclusions about coupled diffusion and adsorption processes. For this purpose, the model of Reyes <i>et al.</i> for FR of gases in mesopores (<i>J. Phys. Chem. B</i>, 1997, <b>101</b>, 614-622) is applied in comparison to the simplified case of effective diffusion. It is shown that diffusion coefficients are obtained in the range of the Knudsen regime, while adsorption is quantified in good agreement with the adsorption capacity derived from the adsorption isotherms. Effective diffusion coefficients are evaluated as a result of the interaction of adsorption and diffusion. This research not only aims to apply the model of Reyes <i>et al.</i> to a homemade volume swing FR method for the first time, but also to further pave the way for the systematic investigation of mesoporous materials using FR and DRIFTS.