No abstract

Cu2O-SiO2 composite aerogel-like adsorbents with different n(Si/Cu) were synthesized by a sol–gel method, followed by drying under atmospheric pressure, and characterized by BET, XRD, SEM, H2-TPR, XRF, and FTIR means. Their adsorption performance for thiophene and benzothiophene in model fuels was investigated with equilibrium and breakthrough adsorption experiments, respectively. The results showed that Cu2O-SiO2 composite aerogel-like adsorbents exhibited an excellent desulfurization performance based on π-complexation between Cu­(I) and thiophenics. The n(Si/Cu) of Cu2O-SiO2 had an obvious effect on their physical properties and consequently desulfurization performance. The BET surface area, pore size, and pore volume decreased with the decrease of n(Si/Cu) (increase of Cu content). Only a part of Cu was incorporated into the materials. The more the Cu­(I) and the higher the specific surface area, the larger the adsorption capacity was. Cu2O-SiO2-50 performed the best, and breakthrough adsorption capacities for benzothiophene and thiophene were 5.78 mg S/gads (0.90 mmol-S/mmol-Cu) and 4.76 mg S/gads (0.74 mmol-S/mmol-Cu), respectively. The adsorption data can be well fitted by both the Langmuir and Freundlich adsorption isotherms. The effect of competitive adsorption of olefins or aromatics on the desulfurization performance of adsorbents was obviously weaker compared with the result in the literature. The spent Cu2O-SiO2 adsorbents can be well regenerated by benzene–n-heptane washing. The breakthrough adsorption capacity of thiophene on the first regenerated Cu2O-SiO2-50 was 71% of that on fresh adsorbent.

Ag2O/SiO2–TiO2 -n aerogel composites with different molar ratios of Si/Ti, prepared by a sol–gel method followed by the ambient pressure drying technique, were used for the adsorptive removal of thiophenic compounds from model fuels, along with Ag2O/SiO2-50. The physicochemical properties of aerogel composites were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) spectroscopy, Brunauer–Emmett–Teller (BET) method, Fourier transform infrared (FT-IR) spectroscopy, NH3 temperature-programmed desorption (TPD), and pyridine (Py) FT-IR spectroscopy. The results indicated that doping Ti into Ag2O/SiO2-50 led to a slight decrease in the specific surface area, an obvious increase in the actual content of Ag, and the appearance of weak Lewis acid centers on the surface. The data for equilibrium adsorption of thiophene over Ag2O/SiO2-50 and Ag2O/SiO2–TiO2-50 were well fitted to the Langmuir and Freundlich isotherm equations. The kinetic experimental data of Ag2O/SiO2–TiO2-50 was well fitted by a pseudo-second-order model. For two adsorbents, negative values of ΔG indicated that the adsorption processes were spontaneous. The adsorption process on Ag2O/SiO2–TiO2-50 was more favorable at higher temperatures, which was contrary to that on Ag2O/SiO2-50. The incorporation of Ti into Ag2O/SiO2-50 can improve the adsorptive desulfurization performance owing to the increase in the actual content of Ag species (π-complexation centers), and thiophenic compounds can be adsorbed via Lewis acid–base interaction and S–Ti binding besides π-complexation. Among Ag2O/SiO2–TiO2-n, Ag2O/SiO2–TiO2-50 performed the best.