Effect of Doping Al on the Desulfurization Performance of Ag/SiO2-Al2O3 Aerogel Composite Adsorbents

Ag/SiO2-Al2O3 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/SiO2. The incorporation of Al in Ag/SiO2 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/SiO2-Al2O3-n increased first and then decreased with the increase in Al content. Doping Al in Ag/SiO2 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/SiO2-Al2O3-n by pi-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/SiO2-Al2O3-100 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.