Effect of B₂O₃ modified Ag/TiO₂-Al₂O₃ adsorbents on the adsorption desulfurization of diesel

Ag/TiO₂-B₂O₃-Al₂O₃ adsorbents with different B₂O₃ loadings (e.g. 5%~20% (w)) were prepared by impregnation. Static adsorption tests were carried out by contacting the adsorbents with commercial diesel containing 245.36mg(S)/L sulfur at ambient conditions to investigate the adsorption desulfurization activity. The results show that Ag/TiO₂-Al₂O₃ modified by B₂O₃ exhibits a great enhancement for the adsorption desulfurization activity. When B₂O₃ (15%) was loaded, 2%Ag/4%TiO₂-15%B₂O₃-Al₂O₃ (w) could achieve the best desulfurization activity with a saturation capacity of 2.36mg(S)/g adsorbent. This is a significant achievement regarding the desulfurization efficiency, especially for commercial diesel without pretreatment. The effects of B₂O₃ on the textural properties, crystal structure and surface acidity properties of the adsorbent were studied by N₂-physisorption, O₂-chemisorption, X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH₃-TPD), Fourier transform infrared spectrometer (FT-IR spectra) and ¹¹B nuclear magnetic resonance (¹¹B-NMR) techniques. Correlating the characterizations with the desulfurization activity, it is found that the adsorption desulfurization activity is well related with the amounts of weak acid sites on the adsorbents. B₂O₃ modification induces larger amounts of BO₄ species and improves the surface weak acidity, resulting in a higher adsorption desulfurization activity.