Pd/SiO2 Aerogel Composite Adsorbents with High Desulfurization Performance
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.
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