Characteristics of sulfur removal by silver-titania adsorbents at ambient conditions

Abstract

Sulfur capacity of SiO 2 , TiO 2 and γ -Al 2 O 3 structures was investigated. Thermal treatment of TiO 2 and γ -Al 2 O 3 in air increased their respective sulfur capacity by 67 and 43%. Sulfur capacity was associated with surface acidity and the improvement attributed to the formation of bronsted acid sites. Addition of 4wt% transition metals further enhanced the sulfur capacity of TiO 2 with Ag indicating the highest increase. Comparison of sulfur capacity of Ag/TiO 2 with other adsorbents was made using JP5 fuel with sulfur concentration of 1172 ppmw. Ag/TiO 2 adsorbent demonstrated a saturation sulfur capacity of 8.20 mg/g. A significant loss in sulfur capacity was observed between real and model fuel compositions. Various factors resulting in this loss was investigated such as the effect of additives, competitive adsorption and the structure of sulfur heterocycles.

Understanding the dispersion of Ag on high surface area TiO2 supports using XPS intensity ratios

“…The latter behavior not being readily observable from those techniques which assume uniform or average population behavior. Of particular note is the fact that the observed heterocycle adsorption trends versus Ag loading agree closely with the dispersion and nucleation trends deduced from XPS-Ag/Ti intensity ratios [1,21].…”

“…Sulfur heterocycle adsorption capacities of different supports and metal loadings have been reported in past studies [1,9,[21][22][23][24][25][26]. A greater adsorption capacity for model fuel with benzothiophene (BT) than jet fuel, JP-5 was observed, this is due to competitive adsorption among all the compounds present in JP5-sulfur compounds and non sulfur aromatic compounds.…”

“…The (1 0 1) surface is also the most thermodynamically stable under clean conditions, while the (1 0 0) surface is thought to be more stable among oxygenated surfaces [45,46], thus, the (1 0 1) surface was used as the basis for the schematic depiction. The introduction of silver ions into the surface of the TiO 2 enhances the sulfur heterocycle adsorption capacity as previously stated [1,21]. The mechanism can be explained by the filling of point defects on the surface of the TiO 2 up to an optimal concentration, i.e.…”

“…Increasing Ag loading monoatomically up to 4 wt% linearly increased capacity after which there was no further increase in capacity with the addition of Ag. Unlike other supports, Ag/TiO 2 showed stable multi-cycle behavior and did not leach into the sample [1,21,22,25].…”

“…Ag/TiO 2 samples prepared according to this procedure have been previously investigated for sulfur adsorption capacity [1,9,[21][22][23][24][25][26]. Efforts included various different supports such as, but not limited to, SiO 2 and Al 2 O 3 and different Ag loadings from 1 wt% to 20 wt%.…”