A frequency response study of thiophene adsorption in zeolite catalysts

The frequency response (FR) technique has been applied to study adsorption processes of thiophene (TP) on NaY zeolite and CeY zeolite. The FR spectra of TP on NaY and CeY were recorded at temperatures between 335 and 473 K and in the pressure range of 0.1-4.0 Torr. On NaY and CeY, adsorption of thiophene (TP) in the supercage is found to be the rate-controlling step and diffusion of benzene in the supercage is the rate-controlling step, respectively. On NaY, the adsorption process by pi-electronic interaction of TP and adsorption via pore-filling mechanism were caught. Adsorption by pi-electronic interaction is not the main sorption process but its effect is significant. While on Ce(3+)y, the adsorption processes relating to the pi-complexation and the direct forming of S-M bond were observed, the adsorption by forming pi-complexation is the main process. The relaxation time of the strong sorption interaction coming from the FR spectrum is two orders magnitude shorter than that of the weak adsorption process and the number of sites available for adsorption of TP in each process is calculated. The value of relaxation time reflects the ability of different processes and concentration of adsorption site. Combining the FR spectra and other methods such as isotherms and Langmuir model, thoroughly understanding of the thiophene adsorption process in zeolites can be got. (c) 2007 Elsevier B.V. All rights reserved.