Determining the Adsorption Sites for Binary Mixtures of p-Xylene and n-Heptane in Silicalite Using FT-Raman Spectroscopy and Temperature-Programmed Desorption

Abstract

FT-Raman spectroscopy and temperature-programmed desorption (TPD) measurements have been used to gain information on the preferred adsorption sites for p-xylene and n-heptane adsorbed within silicalite. FT-Raman spectroscopy is used to probe the location of adsorbed p-xylene, both when pure p-xylene is adsorbed and for the binary mixtures. The TPD measurements in combination with the FT-Raman spectra are used to infer the location of the adsorbed n-heptane. The results on the preferred adsorption sites for pure adsorbates are consistent with those in the literature. The results on binary mixtures show unusual behavior at loadings of four p-xylene/three n-heptane and three p-xylene/four n-heptane molecules per unit cell. In contrast to the behavior for single component adsorption, at these loadings the n-heptane molecules preferentially occupy the straight channels of silicalite, forcing the p-xylene molecules out of their normal preferred site (the channel intersections) and into the zigzag channels. The ...