Deep desulfurization of transportation fuels (gasoline, diesel, and jet fuels) is being mandated by U.S. and foreign governments and is also needed for future fuel cell applications. However, it is extremely difficult and costly to achieve with current technology, which requires catalytic reactors operated at high pressure and temperature. We show that Cu+ and Ag+ zeolite Y can adsorb sulfur compounds from commercial fuels selectively and with high sulfur capacities (by pi complexation) at ambient temperature and pressure. Thus, the sulfur content was reduced from 430 to <0.2 parts per million by weight in a commercial diesel at a sorbent capacity of 34 cubic centimeters of clean diesel produced per gram of sorbent. This sulfur selectivity and capacity are orders of magnitude higher than those obtained by previously known sorbents.

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New sorbents for the desulfurization of liquid fuels were developed using π-complexation. Vaporphase adsorption isotherms were investigated to understand the interaction between benzene/ thiophene and various kinds of sorbents, including Ag-Y, Cu-Y, Na-Y, H-USY, Na-ZSM-5, activated carbon, and modified activated alumina. Compared to Na-Y, Cu-Y and Ag-Y adsorbed significantly larger amounts of both thiophene and benzene at low pressures, as a result of π-complexation with Cu + and Ag + . Molecular orbital calculations confirmed that the relative strengths of π-complexation lie in the order thiophene > benzene and Cu + > Ag + . The experimental heats of adsorption for π-complexation are in excellent agreement with theoretical molecular orbital predictions. Na-ZSM-5 and activated carbon could also adsorb small amounts of thiophene and benzene at low pressures. The sorbent capacities for thiophene at the low pressure of 2.3 × 10 -5 atm were 0.92 molecule/Cu + and 0.42 molecule/Ag + and followed the order Cu-Y and Ag-Y . Na-ZSM-5 > activated carbon > Na-Y > modified alumina and H-USY. The separation factors of thiophene over benzene (at low concentrations of thiophene) calculated from pure component adsorption isotherms exhibited the trend Ag-Y > Na-ZSM-5 > Cu-Y ≈ activated carbon . Na-Y . H-USY ≈ modified activated alumina.

Fuel technology Fuel technology V 0400Desulfurization of Transportation Fuels with Zeolites under Ambient Conditions.-Cu + and Ag + zeolite Y, prepared by ion exchange of NaY zeolite with Ag + or Cu 2+ , adsorb sulfur compounds from commercial fuels (gasoline, diesel, and jet fuels) selectively and with high sulfur capacities at ambient temperature and pressure. The sulfur content in a commercial diesel is reduced from 430 to <0.2 ppm (by weight) at a sorbent capacity of 34 cm 3 of clean diesel produced per gram of sorbent. This sulfur selectivity and capacity are orders of magnitude higher than those obtained by previously known

Spillover of hydrogen on nanostructured carbons is a phenomenon that is critical to understand in order to produce efficient hydrogen storage adsorbents for fuel cell applications. The spillover and interaction of atomic hydrogen with single-walled carbon nanotubes (SWNTs) is the focus of this combined theoretical and experimental work. To understand the spillover mechanism, very low occupancies (i.e., 1 and 2 H atoms adsorbed) on (5,0), (7,0), (9,0) zigzag (semiconducting) SWNTs and a (5,5) armchair (metallic) SWNT, with corresponding diameters of 3.9, 5.5, 7.0, and 6.8 A, were investigated. The adsorption binding energy of H atoms depends on H occupancy, tube diameter, and helicity (or chirality), as well as endohedral (interior) vs exohedral (exterior) binding. Exohedral binding energies are substantially higher than endohedral binding energies due to easier sp(2)-sp(3) transition in hybridization of carbon on exterior walls upon binding. A binding energy as low as -8.9 kcal/mol is obtained for 2H atoms on the exterior wall of a (5, 0) SWNT. The binding energies of H atoms on the metallic SWNT are significantly weaker (about 23 kcal/mol weaker) than that on the semiconductor SWNT, for both endohedral and exohedral adsorption. The binding energy is generally higher on SWNTs of larger diameters, while its dependence on H occupancy is relatively weak except at very low occupancies. Experimental results at 298 K and for pressures up to 10 MPa with a carbon-bridged composite material containing SWNTs demonstrate the presence of multiple adsorption sites based on desorption hysteresis for the spiltover H on SWNTs, and the experimental results were in qualitative agreement with the molecular orbital calculation results.

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CuY and AgY zeolites were studied as selective sorbents for the desulfurization of liquid fuels. Thiophene and benzene were used as the model system, and vapor-phase isotherms were measured. Compared to NaY, CuY and AgY adsorbed significantly larger amounts of both thiophene and benzene at low pressures as a result of π-complexation with Cu+ and Ag+. On a per-cation basis, more thiophene was adsorbed by Cu+ than by Ag+, e.g., 0.92 molecule/Cu+ vs 0.42 molecule/Ag+ at 2 × 10-5 atm and 120 °C. Molecular orbital calculations confirmed the relative strengths of π-complexation as thiophene > benzene and Cu+ > Ag+. The experimental heats of adsorption for π-complexation are in qualitative agreement with theoretical predictions.

Hydrogen storage capacity by hydrogen spillover on metal-doped carbons can be significantly enhanced by introducing surface oxygen functional groups to the carbon. It is shown that the enhancement is greater by oxygen plasma treatment compared to air oxidation because different surface groups were formed. Oxygen plasma treatment generated mainly semiquinone (CdO) groups while air oxidation formed mainly hydroxyl (C-OH) groups. Experimental heats of adsorption, X-ray photoelectron spectroscopy (XPS) analyses, and ab initio molecular orbital calculations showed that the binding energies between the spiltover hydrogen and the different groups followed the following order: lactone > semiquinone > carboxyl > basal plane. Thus, the H 2 storage capacity at 298 K and 10 MPa was increased from 1.17 wt % (without O 2 treatment) to 1.74 wt % on Pt-doped on a templated carbon that was pretreated with O 2 plasma. Similar enhancements were seen on Pt doped on a superactivated carbon, AX-21. However, there was a decrease in storage capacity during the first three adsorption-desorption cycles (at 298 K and 10 MPa). The capacity decreased from 1.74 wt % to 1.30 wt % and remained unchanged after three cycles. XPS results showed that this decrease was caused by the very strong (and irreversible) binding of the spiltover hydrogen with the lactone groups (HO-CdO). Nonetheless, the main groups of semiquinone remain functional as receptor sites upon cycling, and the 1.3 wt % storage capacity is among the highest reversible capacities reported in the literature.