A frequency response study of thiophene adsorption on HZSM-5

The adsorption mechanism and dynamical parameter of thiophene on HZSM-5 were studied by frequency response (FR). The FR spectra of thiophene on HZSM-5 (Si/Al = 25, 38, 50) were recorded at pressures between 26.6 Pa and 798 Pa in the temperature of 302-623 K range. Results suggest that the adsorption process was the rate controlling step in the FR spectra, and there were two different adsorption processes. Those two processes were attributed to adsorption process of thiophene on SiOH sites (high frequency adsorption) and strong Brönsted acid sites (low frequency adsorption). According to the Yasuda adsorption model and Langmuir rate model, the low frequency sorption did not obey Langmuir model, High frequency adsorption obeyed Langmuir model, which was single layer adsorption. The adsorption sites of low frequency (Ns (1)) was 0.58 mmol g−1 and that of high frequency (Ns (2)) was 0.92 mmol g−1 at 373 K. High frequency adsorption was the main adsorption process. High frequency adsorption did not reached saturation adsorption between 302 K and 623 K, the intensity of the FR spectra reached the maxima at θe(j)=0.5.

Research highlights▶ The frequency response method is used to study adsorption of thiophene in HZSM-5. ▶ This method is effective to study two parallel adsorption processes in one system. ▶ The dynamic information and sorption sites of each adsorption process are achieved. ▶ Isotherms and Langmuir equations are used to explore adsorption mechanism.