Effectiveness of metal–organic frameworks for removal of refractory organo-sulfur compound present in liquid fuels G. Blanco-Brieva a , J.M. Campos-Martin a , S.M. Al-Zahrani b , J.L.G. Fierro a,⇑ a Sustaninable Energy and Chemistry Group (EQS), Instituto de Catálisis y Petroleoquímica, CSIC, c/Marie Curie, 2 Cantoblanco, 28049 Madrid, Spain 1 b Chemical Engineering Department, College of Engineering, King Saud University, Riyadh, Saudi Arabia article info Article history: Received 5 February 2010 Received in revised form 6 August 2010 Accepted 11 August 2010 Available online 24 August 2010 Keywords: Metal–organic frameworks Sulfur compounds Adsorption Isotherms abstract Adsorption of organo-sulfur compounds present in liquid fuels on metal–organic framework (MOF) com- pounds is an efficient alternative to the conventional hydrodesulfurization process. It has been demon- strated that the extent of dibenzothiophene (DBT) adsorption at temperatures close to ambient (304 K) is much higher on MOFs systems than on the benchmarked Y-type zeolite. In addition, the DBT adsorp- tion capacity depends strongly on the MOF type as illustrated by the much higher extent of adsorption observed on the copper- (C300) and Al-containing (A100) MOF systems than on the Fe-containing (F300) MOF counterpart. With the aim to investigate the operation in consecutive cycles, the MOFs used in adsorption experiments were regenerated. In addition, the remaining S-containing compounds were identified and quantified by photoelectron spectroscopy (XPS). Examination of S2p core-level spectrum of the adsorbed S-compounds of regenerated MOFs pointed out that a fraction of these molecules become oxidized into S(VI) species. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The sulfur content in fuels is an environmental concern because upon combustion sulfur is converted to SO x , which not only con- tributes to acid rain, with have a negative effect on human health and in the environment, but also poisons catalytic converters for the treatment of exhaust emissions, which are very expensive due to are based on noble metals [1]. For all these reasons, more stringent environmental regulations reduce the sulfur concentra- tion limits in liquid fuels [2] (diesel and gasoline), and it will cer- tainly be lowered in the near future. The traditional industrial process is the hydrodesulfurization (HDS) [3], that eliminates effi- ciently nonaromatic sulfur compounds and thiophenes, but is less effective by more sterically hindered benzothiophene (BT), diben- zothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT) fuel contaminants and have limitations in terms of product quality and cost, which are undesirable to refiners [4]. To remove these undesirable S-containing compounds or to convert them into more innocuous forms, various complementary or alternative processes different from HDS have been proposed to produce ultra-low sulfur diesel (ULSD). Among them, oxidative microbial transformations [5], physical extraction with a liquid [6], selective adsorption on suitable materials [7–10] and catalytic oxidation [11,12] remain prominent. Specifically, the adsorption of S-compounds has attracted much attention due to some advantages, such as mild operation condi- tions (temperatures close to ambient, atmospheric pressure) and no need of hydrogen or oxygen. Many studies have been under- taken to develop adsorbents for the desulfurization of transporta- tion fuels using zeolites [7,8] mesoporous materials [9] and activated carbons [10,13–15]. Recently, Ma and Yang [16] reported a comparison of ion-exchanged zeolite and metal halide-impreg- nated carbon for selective adsorption of desulfurization in liquids fuels. The results indicated that metal halide-impregnated carbon has a higher adsorption capacity than that of ion-exchanged zeolite for refractory sulfur compounds. Kim et al. [17] used silica–alu- mina gel-impregnated Ni, activated alumina, and activated carbon for selective adsorption in the desulfurization of model fuels con- taining sulfur compounds, aromatic compounds, and nitrogen compounds. In this study, activated carbon showed higher adsorp- tion capacity and selectivity for both sulfur and nitrogen com- pounds, especially for the sulfur compounds with methyl groups. In addition, it was shown that the adsorption capacity of activated carbon for desulfurization and denitrogenation of straight-run gas oil (SRGO) increased in proportion to the oxygen content, surface area, and total pore volume of activated carbon adsorbent [14]. From the studies using activated carbons it was concluded that various physical properties, such as BET specific area, total pore volume, and micropore volume, can be correlated with sulfur 0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.08.008 ⇑ Corresponding author. Fax: +34 91 585 4760. E-mail address: jlgfierro@icp.csic.es (J.L.G. Fierro). 1 http://www.icp.csic.es/eqs/ Fuel 90 (2011) 190–197 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel