Ag/SiO 2 −Al 2 O 3 aerogel composites with different molar ratio of Si to Al were prepared by the sol−gel synthesis followed by drying under atmospheric pressure and then characterized by XRD, FT-IR, BET, SEM, XRF, TG-DTG, and Py-FTIR, respectively. The effect of doping Al on their physicochemical properties and adsorption desulfurization performance was investigated in comparison with Ag/ SiO 2 . The incorporation of Al in Ag/SiO 2 resulted in a gradual decrease in the specific surface area, an increase in the actual content of Ag, and an appearance of Bronsted acid centers. The actual content of Ag in Ag/SiO 2 −Al 2 O 3 -n increased first and then decreased with the increase in Al content. Doping Al in Ag/SiO 2 led to an improvement in the adsorption capacity and the adsorptive selectivity for thiophene at the presence of toluene and cyclohexene, as well as the solvent washing regeneration performance, attributed to the adsorption of thiophenics on Ag/SiO 2 −Al 2 O 3 -n by π-complexation of Ag(I) and the acid−base interaction of Lewis and Bronsted centers with thiophenics simultaneously, and the increase in the actual content of Ag in the adsorbents. Ag/SiO 2 −Al 2 O 3 -100 had the largest adsorption capacity for thiophene and benzothiophene, 12.2 mg of S/g ads (0.57 mmol of S/mmol of (Ag + Al)) and 17.7 mg of S/g ads (0.53 mmol of S/mmol of (Ag + Al)), respectively.

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Pd/SiO2-n aerogel composites with different Si/Pd mole ratios (n(Si/Pd)) were synthesized by a sol–gel method followed by drying in the atmosphere to adsorb thiophenic compounds from model oils. For Pd/SiO2-n, doping Pd species in SiO2 aerogels led to the appearance of weak Lewis acidic sites on the surface. The adsorption capacity of Pd/SiO2-n was significantly higher than that of pure SiO2, owing to the π-complexation, S–M bonding, and acid–base interaction between Pd2+ and thiophenic compounds. Among them, the capacity of Pd/SiO2-318 was the highest, 4.76 mg S/gads (i.e., 9.37 μmol S/μmol Pd), which was obviously higher than that of sorbents reported such as Pd/activated carbon and Pd/Al2O3, based on the amount of thiophene adsorbed per unit active centers. In the presence of aromatics and olefins, the selectivity of Pd/SiO2 for thiophene was higher than that of Ag/SiO2 and Cu/SiO2 reported, attributed to the stronger S–Pd bonding than the S–Ag and S–Cu bonding. The equilibrium adsorption data of thiophene onto Pd/SiO2-318 were well simulated with the Langmuir and Freundlich models. Combined with thermodynamic results, it can be found that the low temperature was favorable for the adsorption of thiophene. Pd/SiO2 exhibited a good regeneration performance after solvent washing.

Amine-modified SiO 2 hybrid aerogel desulfurization adsorbents with varied Si/N molar ratios (SiO 2 -NH 2 -n) were prepared via the sol−gel method followed by the atmospheric drying technique. SiO 2 -NH 2 -n aerogels were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), in situ Fourier transform infrared (FT-IR), and N 2 adsorption−desorption. The desulfurization performances of SiO 2 -NH 2 -n were studied by the batch and breakthrough adsorption experiments. SiO 2 -NH 2 -n exhibited an obvious improvement in adsorption capacity for thiophenics compared with SiO 2 aerogel due to the hydrogen bonding between thiophenics and amino groups. Among them, SiO 2 -NH 2 -8 had the best performance, and the adsorption capacities for thiophene, benzothiophene, and dibenzothiophene were 6.8, 9.5, and 10.2 mg S/g ads , respectively. No effect of toluene and cyclohexene on the adsorption of SiO 2 -NH 2 -8 for thiophene was observed. The equilibrium adsorption data of SiO 2 -NH 2 -8 for thiophene were well fitted by the Freundlich model, indicating that multilayer adsorption occurred on the heterogenetic surface of SiO 2 -NH 2 -8. The kinetic adsorption data of SiO 2 -NH 2 -8 for thiophene could correlate properly with the pseudo-second-order kinetic model, suggesting that the rate-controlling steps involve surface adsorption. The saturated SiO 2 -NH 2 -8 could be regenerated completely via heating at 393 K for 12 h, and the regenerated SiO 2 -NH 2 -8 afforded 100% breakthrough adsorption capacity for thiophene.

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