Traditional and recently emerged nanoporous adsorbents for deep desulfurization of liquid hydrocarbon fuels are summarized.

Due to their versatility, nontoxicity, and low cost, much attention has been paid to the fabrication of Cu(I) sites on various supports. High-temperature autoreduction is a widely used method for selective conversion of supported Cu(II) to Cu(I). However, aggregation of copper species usually takes place during autoreduction, which seriously decreases the yield of Cu(I) and compromises the activity of resultant materials. In the present study, a strategy was developed for the effective formation and dispersion of Cu(I) sites by constructing a confined space in silica nanopores, for the first time. A layer of porous silica is coated on the precursor (namely CuO-modified SBA-15) before autoreduction, and CuO is thus confined between original pore walls and newly formed silica layers. Owing to the energy barrier offered by the confined space, the dispersion degree of copper species after autoreduction is well improved. Furthermore, the yield of Cu(I) can reach ∼82% for the samples coated with silica, which is obviously higher than that for the sample without a silica layer (∼54%). More importantly, abundant pores with a uniform size of ∼2.5 nm are successfully generated on the silica layer under the direction of cetyltrimethylammonium bromide (CTAB). This endows the resultant materials with active sites highly accessible to guest molecules. The materials were also applied to the adsorption of CO by using π-complexation between CO and Cu(I) sites. The results show that these materials exhibit good performance for selective adsorption of CO from H₂, CH₄, and N₂, which is apparently better than the material without a silica layer with regard to both capacity and selectivity.

Functionalization of metal–organic frameworks (MOFs) with Cu(I) sites is extremely desirable for various applications including adsorption, catalysis, and sensing. The traditional method for the conversion of supported Cu(II) to Cu(I) is high-temperature autoreduction (HTA), which produces Cu(I) with an unsatisfactory yield (ca. 50%) but requires quite harsh conditions (e.g. 700 °C, 12 h) that are unsuitable for MOFs. Here we report the rational design of an efficient, controllable strategy for the conversion of supported Cu(II) to Cu(I) by using vapor-induced selective reduction (VISR), in which vapors of weak reducing agents (e.g. methanol) diffuse into the pores of MOFs and interact with Cu(II) precursors. This strategy allows the fabrication of Cu(I) sites with a 100% yield without the formation of Cu(0) at much lower temperatures (e.g. 200 °C, 6 h) and subsequently preserves the structure of MOFs well. Due to the abundant Cu(I) sites and high porosity of MOF supports, the obtained materials exhibit excellent performance in adsorptive desulfurization with regard to capacity, selectivity, and recyclability.

Deep desulfurization of transportation fuels via π-complexation adsorption is an effective method for the selective capture of aromatic sulfur compounds. Taking into consideration that the desulfurization of transportation fuels proceeds in the liquid phase, separation and recycling of adsorbents should be greatly facilitated if the adsorbents were endowed with magnetism. In this paper, magnetically responsive core–shell π-complexation adsorbent microspheres, AgNO₃/Fe₃O₄@mSiO₂ (mSiO₂ denotes mesoporous silica), which comprises a core of magnetite particles and a shell of mesoporous silica dispersed with AgNO₃, was developed for the first time. The silica shell exhibits highly open mesopores with perpendicularly aligned pore channels, large surface area (694 m² g⁻¹) and uniform pore size (2.3 nm), which is quite beneficial to the accommodation of Ag(I) active species. As a result, AgNO₃ can be well dispersed in the pores of silica shells and are highly accessible to adsorbate molecules. Our results show that the adsorbent is active in the adsorptive removal of a typical aromatic sulfur compound, thiophene, via π-complexation under ambient conditions. More importantly, the superparamagnetism allows the adsorbent to be separated conveniently from the adsorption system in several seconds by the use of an external field. After desulfurization, the adsorbents were regenerated by washing with isooctane and subsequent thermal dispersion in Ar. The regenerated adsorbent after six cycles still shows a good adsorption capacity (0.145 mmol g⁻¹ or 4.64 mg g⁻¹), which is comparable to the fresh adsorbent (0.147 mmol g⁻¹ or 4.70 mg g⁻¹). The magnetically responsive π-complexation adsorbent may be a promising candidate for the deep purification of transportation fuels.