Facile fabrication of superior Pd and Ce containing SiO2 aerogel composite adsorbents for deep desulfurization of model fuels and aromatics

A series of PdO/CeO 2 /SiO 2 -z aerogel composites with different molar ratio of Si/Ce were facilely fabricated via sol-gel method combined with atmospheric drying technology, where a major of Ce 3+ species could be oxidized to Ce 4+ species by adding hydrogen peroxide. They were used to remove thiophenics from model fuels and aromatics, compared with PdO/SiO 2 and CeO 2 /SiO 2 aerogel composites. Adding Ce and Pd led to an appearance of weak Lewis acid centers on the surface of adsorbents. Compared with PdO/SiO 2 and CeO 2 /SiO 2 , the adsorption capacity of PdO/CeO 2 /SiO 2 -z significantly increased, in which PdO/CeO 2 /SiO 2 -100 performed best and the adsorption capacity for thiophene was 15.0 mg-S/g ads , which was about the sum of PdO/SiO 2 -636 and CeO 2 /SiO 2 -100. The case was attributed to π-complexation of Pd 2+ and S-M (Pd, Ce, acted as Lewis acid centers) bond (σ) with thiophenics, where the adsorption process was dominated by S–Ce bond. Combined with the same chemical state of Pd and Ce in single metal and bimetal adsorbents verified by XPS , it can be deduced that no synergistic interaction between Pd and Ce species was formed in the adsorption process. PdO/CeO 2 /SiO 2 -100 exhibited a higher resistance for competitive adsorption of aromatics and a good solvent washing regeneration performance. The adsorption process of PdO/CeO 2 /SiO 2 -100 for thiophene was well fitted by Langmuir isothermal and pseudo-secound-order model and were spontaneous and endothermic. The solvents (n-heptane, benzene and p-xylene) have no obvious effect on the adsorption thermodynamics and kinetics of PdO/CeO 2 /SiO 2 -100.