Abstract
Silver–titania (Ag/TiO2) adsorbents, in the range of 4wt% Ag, display high selectivity toward sulfur heterocyclic compounds from complex fuel streams containing other aromatics. An experimental investigation of Ag on TiO2 has been undertaken to understand the state of dispersion and growth of Ag. XPS is one of the more promising characterization tools for the state of dispersion. Silver loading from 1wt% to 20wt% on 150m2/g titania was investigated. Ag/Ti intensity ratios increased linearly with Ag content up to 4wt% and increased less significantly thereafter from 8wt% to 20wt% indicating nucleation and growth of Ag crystallites. Inelastic mean free path (IMFP) calculations were used to estimate Ag crystallite size based on the attenuation of the Ag signal, realizing in this regime there is insufficient Ag to attenuate background titania. At 4, 8, 12, and 20wt% the estimated average crystallite sizes were 0.35, 0.71, 0.84, and 1.11nm respectively. Ag loadings up to 4wt% were present in the form of Ag+1 adatoms presumably occupying TiO2 surface defects. Saturation of surface TiO2 defects is in good agreement with quantitative sulfur heterocycle adsorption.
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