Air‐Promoted Adsorptive Desulfurization over Ti0.9Ce0.1O2 Mixed Oxides from Diesel Fuel under Ambient Conditions

Herein, we demonstrate the high-capacity adsorptive desulfurization of commercial diesel by using TiO2-CeO2 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. Since 2006, US EPA regulations have required that the sulfur content in diesel fuel be lower than 15 parts per million by weight (ppmw). 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). Therefore, ultra-deep diesel desulfurization is an important research subject worldwide. One energy-efficient desulfurization approach for producing ultra-clean fuels with sulfur concentrations 1000 ppmw). The Ti/Ce ratio was optimized to 9:1 for maximum sorption capacity. However, the sorption capacity over the Ti0.9Ce0.1O2 sorbent was quite low for low-sulfur diesel fuels. Computational studies suggested that chemisorbed oxygen species on the TiO2 surface played an important role in promoting ADS, thus suggesting highly selective adsorption through the formation of sulfoxide/sulfone species. Our previous computational work also suggested a number of possible effects of Ce addition to TiO2, although it only examined the adsorption thermodynamics and was inconclusive regarding the key impact of Ce addition. We hypothesized that the introduction of chemisorbed oxygen species during the ADS process could increase the sorption capacity for TiO2-CeO2 mixed oxides. We were also seeking a mechanistic answer for the increased sorption capacity and adsorption rate on the addition of Ce to TiOx adsorbents. A combined experimental/ quantum-theoretical approach was used to gain further understanding of the adsorption mechanism. Herein, we report the air-promoted ADS from commercial diesel over Ti0.9Ce0.1O2 mixed oxides under ambient conditions. Introduced air chemically transformed the sulfur compounds into oxidized sulfur species, which were identified by sulfur Kedge X-ray absorption near-edge structure (XANES) analysis. Moreover, control studies demonstrated the unique performance of Ti0.9Ce0.1O2 mixed oxides in the air-promoted ADS reaction. A catalytic adsorption mechanism with O vacancies as [a] J. Xiao, S. Sitamraju, Prof. Y. Chen, Prof. M. Janik, Prof. C. Song Clean Fuels and Catalysis Program EMS Energy Institute Pennsylvania State University 211 CUL, University Park, PA 16802 (USA) Fax: (+1)814-865-3573 E-mail : csong@psu.edu [b] J. Xiao, S. Sitamraju, Prof. Y. Chen, Prof. C. Song Department of Energy and Mineral Engineering Pennsylvania State University 211 CUL, University Park, PA 16802 (USA) [c] Prof. M. Janik, Prof. C. Song Department of Chemical Engineering Pennsylvania State University 104 Fenske Laboratory, University Park, PA 16802 (USA) Fax: (+1)814-865-7846 E-mail : mjanik@psu.edu Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300329.