The role of surface acidity in adsorption of aromatic sulfur heterocycles from fuels

Abstract

The objective of this work is to investigate the relationship between sulfur adsorption capacity and surface acidity of supported silver oxide adsorbents from liquid hydrocarbon fuels. Inherently acidic supports such as TiO2 and Al2O3 developed sulfur adsorption capacity following activation in air at temperatures above 350°C. Addition of Ag to these supports further increased sulfur adsorption capacity by ∼40%. Efforts were made to understand the thermal activation process and the sulfur adsorption mechanism. Breakthrough characteristics of various hetero aromatic molecules revealed that the strengths of adsorption increased with electronegativities of the heteroatoms. Sulfur adsorption capacities of these adsorbents were progressively reduced when poisoned with increasingly basic molecules. Surface acidity was measured using NH3 chemisorption and titration with 2,6-lutidine. Interactions of probe molecules on acid centers were also observed from IR spectroscopy where both Bronsted and Lewis centers were observed. However interactions with 2,6-lutidine and trimethyl chlorosilane indicated that the active centers involved in sulfur adsorption were primarily Bronsted in nature. A clear correlation between activation temperature, surface acidity, and sulfur adsorption capacity was established for both blank and Ag loaded samples.