Air‐Promoted Adsorptive Desulfurization over Ti_0.9Ce_0.1O₂ Mixed Oxides from Diesel Fuel under Ambient Conditions

Abstract

Herein, we demonstrate the high-capacity adsorptive desulfurization of commercial diesel by using TiO 2 -CeO 2 mixed-oxide adsorbents with the addition of air to the fuel and we use density functional theory calculations to explain the unique chemical functionality of the absorbents by detailing a new catalytic adsorption mechanism. The ultra-deep desulfurization of diesel fuel has attracted widespread attention, owing to the stringent government regulations for sulfur content in the transportation fuels for the protection of the environment and human health.[1] Since 2006, US EPA regulations have required that the sulfur content in diesel fuel be lower than 15 parts per million by weight (ppmw). [1a,b] Moreover, diesel fuel has been considered as a preferable feedstock for some on-site and on-board fuel-cell applications, owing to its high energy density, ready availability with existing infrastructures, and safety in terms of its delivery and storage. However, sulfur concentrations higher than 1 ppmw lead to the poisoning of reforming catalysts, water-gas-shift catalysts in fuel processing, and electrodes of proton-exchange membrane fuel cells (PEMFCs).[2] Therefore, ultra-deep diesel desulfurization is an important research subject worldwide.[3]One energy-efficient desulfurization approach for producing ultra-clean fuels with sulfur concentrations < 1 ppmw is selective adsorption. Selective adsorption involves the preferential adsorption of organosulfur compounds onto a solid adsorbent. Another approach, adsorptive desulfurization (ADS), provides a promising path for decreasing the sulfur content to less than 1 ppmw under ambient or mild conditions without the use of H 2 . To date, several attempts have been made to develop adsorbents for the desulfurization of liquid fuels, including pcomplexation sorbents, [4] immobilized p-acceptor sorbents, [5] metal-organic frameworks (MOFs), [6] Ni-based sorbents, [7] graphene and oxygen-functionalized carbon sorbents, [8] and softacid-supported sorbents.[9] However, all of these sorbents have drawbacks for the selective ADS from current commercial diesel fuel for the production of ultra-clean fuel under ambient conditions. These challenges include: 1) weak adsorption affinity, owing to steric hindrance of the refractory alkylated sulfur compounds, [10] and 2) poor adsorption selectivity, owing to competitive adsorption between trace amounts of sulfur compounds (< 15 ppmw) and relatively large amounts of polyaromatics (5-10 wt. %).[11] Therefore, new ADS approaches have to be developed for selective ADS from commercial diesel fuel to achieve ultra-clean fuel with sulfur content below 1 ppmw.Metal oxides have been widely used in adsorption and separation processes, owing to their unique advantages, such as regenerability, controllable composition and functionalities, and tunable surface area and pore size. Metal oxides have shown great promise for hot-coal-gas desulfurization through high temperature sulfidation, [11, 12] yet their use in liquid-phase desulfurization ...

Preparation of CuCl@AC with high CO adsorption capacity and selectivity from CO/N2 binary mixture

“…Adsorption is considered to be one of the most promising technologies for the separation and purification of CO (Izumi et al 2005) as it is able to selectively adsorb or accumulate CO from gas mixture over an adsorbent under ambient conditions (Rakić et al 2005;Park et al 2014;Xiao et al 2013). For an effective adsorption technology, adsorbent plays the key role (Xiao et al 2014).…”

Active Sites on Ti–Ce Mixed Metal Oxides for Reactive Adsorption of Thiophene and Its Derivatives: A DFT Study

“…7 The presence of sulfoxides was indicated by S-XANES analysis of the spent sorbent. 7 Our previous computational studies showed that the adsorption of thiophenic compounds was more favorable in the presence of excess surface oxygen, based solely on adsorption thermodynamics. 8,9 Our earlier studies suggested a difficulty in generating oxygen-rich sites on the surface.…”

“…Surface O vacancies, however, serve as active sites to trap O 2 and allow for subsequent adsorption for thiophene. 7 Schaub et al reported STEM results showing that oxygen could be molecularly adsorbed into surface vacancies. 19 Our DFT results showed that molecular oxygen adsorption is favorable, generating a M−O−O−M group (M =Ti, Ce) on the surface (step 2 in Figure 1).…”

Air‐promoted adsorptive desulfurization of diesel fuel overTi‐Ce mixed metal oxides

“…In our previous communication, sulfoxides were identified as the predominant sulfur species on the spent Ti 0.9 Ce 0.1 O 2 mixed oxides adsorbent, suggesting oxygen molecule in air initiates or promotes the chemical transformation of the refractory sulfur compounds to sulfoxides. The sulfoxides were formed on the surface of the adsorbent via catalytic air oxidation of fuel; the formed sulfoxides remained on the surface of Ti‐Ce metal oxides rather than in the bulk liquid.…”

“…Metal oxides have been extensively studied for hot coal gas desulfurization to remove hydrogen sulfide (H 2 S) via high temperature sulfidation . We previously reported that air can increase ADS capacity over a mixed Ti 0.9 Ce 0.1 O 2 adsorbent under ambient conditions through promotion of the chemical transformation of organosulfur compounds to sulfoxides . Our density functional theory (DFT) calculations suggested that chemisorbed oxygen on the TiO 2 surface plays an important role for ADS providing an O‐source for chemical transformation of sulfur compounds over metal oxides.…”