Effect of cyclohexene on thiophene adsorption over NaY and LaNaY zeolites

NaY and LaNaY were used as adsorbents to remove thiophene from model gasoline (MG) with and without cyclohexene (CHE) by static adsorption experiments at room temperature (RT). The adsorbents were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 physisorption and pyridine infrared spectrum (IR). The adsorption experiments show that the desulfurization performance of NaY decreases with the rise of CHE concentration in MG, whereas that of LaNaY first increases then declines. FT-IR spectra of thiophene adsorption indicate that thiophene is mainly adsorbed on NaY via π electron interaction, but adsorbed on LaNaY via π electron interaction, La–S direct interaction and protonation of thiophene. The Brönsted acid sites of LaNaY are found to play a crucial role and be responsible for the protonation of either thiophene or CHE molecules, which results in the alkylation reactions between thiophene and CHE in MG. The gas chromatograph–sulfur chemiluminescence detector (GC–SCD) and ultraviolet–visible (Uv–vis) spectra results also confirm the formation of alkylated thiophenes. The improved desulfurization over LaNaY may be attributed to the formation of alkylated thiophenes, owing to the larger molecular sizes and the higher electron densities on sulfur atoms of the alkylated thiophenes.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The sulfur removal on LaNaY exhibits a volcano curve with the adding of cyclohexene. ► The acidity of LaNaY plays a crucial role in thiophene/cyclohexene adsorption. ► The formation of alkylated thiophenes is confirmed by GC–SCD and Uv–vis. ► The alkylated thiophenes are likely responsible for the high selectivity of LaNaY.