Harvesting clean energy from fuel feedstocks is of paramount significance in the field of environmental science. In this dynamic area, desulfurization provides a valuable contribution by eliminating sulfur compounds from fuel feedstocks to ensure the utilization of fuels without the emission of toxic sulfur oxides (SOx gases). Nonetheless, the inadequacy of the current industrial technique (hydrodesulfurization, HDS) in the removal of refractory sulfur (RS) compounds and the stringent rules imposed on the fuel sulfur level have kindled research on other desulfurization methods like oxidative desulfurization (ODS). With the capacity of eliminating RS compounds under mild conditions, ODS is endorsed as a suitable replacement or complementary to HDS. ODS, in general, consists of two steps: (i) oxidation and (ii) extraction. The oxidation of sulfur compounds is carried out using a suitable catalyst (hereafter termed as an ODS catalyst) in the presence of an oxidant. Choosing a suitable ODS catalyst for industrial applications is still a quest among the various types of catalysts reported so far. With this outline, herein, all the types of ODS catalysts along with their synthetic methods, reactivity and mechanistic insights are reviewed. The activity of ODS catalysts could be influenced by factors like the type of RS compound, solvent, fuel, etc. and those factors are reviewed. The effects of ionic liquids, light, and ultrasound on the performance of ODS catalysts are also briefly summarized. The opportunities and challenges for ODS catalysts are comprehensively explicated in the end. Through this review, systematic information about the types of ODS catalysts including the basic definition, preparative methods, reactivity and mechanism can be comprehended. Furthermore, this review reveals the merits and demerits related to highlighting catalytic ODS as a replacement or complementary to HDS.

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A comprehensive review on oxidative desulfurization catalysts targeting clean energy and environment

Zeolites for adsorptive desulfurization from fuels: A review

Proliferating energy consumption, particularly of fossil fuels, has led to an increasing generation of pollutants; many of these harmful products have been of serious environmental concern. While e...

Advanced Hydrodesulfurization Catalysts: A Review of Design and Synthesis

In this work, we have rationally designed and originally developed a novel monolith de-NOx catalyst with nickel foam as the carrier and three dimensional hierarchical MnO2@NiCo2O4 core–shell nanowire arrays in situ grown on the surface via a two-step hydrothermal process with a post calcination treatment. The catalysts were systematically examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, elemental mapping, ion sputtering thinning, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, H2 temperature-programmed reduction, NH3/NO + O2 temperature-programmed desorption measurements and catalytic performance tests. The results indicate that the nanowire is composed of hollow NiCo2O4 spinel as the core and MnO2 nanoparticles as the shell layer. By ingeniously making the hierarchical Ni–Co oxide nanowires as the support for manganese oxides, the MnO2@NiCo2O4@Ni foam catalyst not only takes advantage of the high surface area of Ni–Co nanowires to achieve high loading amounts as well as high dispersion of manganese oxides, but also makes use of the synergistic catalytic effect between Ni, Co and Mn multiple oxides, and exhibits excellent low-temperature catalytic performance in the end. In addition, with the structure and morphology well maintained under long term steady isothermal operation, the catalyst is able to sustain high NO conversion and exhibits superior catalytic cycle stability and good H2O resistance. Considering all these favorable properties, the MnO2@NiCo2O4@Ni foam catalyst could serve as a promising candidate for the monolith de-NOx catalyst at low temperatures and the rational design of in situ synthesis of 3D hierarchical monolith catalysts also puts forward a new way for the development of environmental-friendly and highly active monolith de-NOx catalysts.

Rational design and in situ fabrication of MnO2@NiCo2O4 nanowire arrays on Ni foam as high-performance monolith de-NOx catalysts

Using a traditional aqueous solution ion exchange method under a protecting atmosphere of N2, a series of Fe/SSZ-13 catalysts with various Fe loadings were synthesized. UV–vis, EPR, and Mossbauer spectroscopic methods, coupled with temperature-programmed reduction and desorption techniques, were used to probe the nature of the Fe sites. The major Fe species are extraframework Fe(III) species: [Fe(OH)2]+ (monomeric) and [HO–Fe–O–Fe–OH]2+ (dimeric). Larger oligomers with unknown nuclearity, poorly crystallized Fe oxide particles, together with isolated Fe2+ ions, are minor Fe-containing moieties. Reaction rate and Fe loading correlations, and temperature and Fe loading effects on SCR selectivities, suggest that isolated Fe3+ ions are the active sites for low-temperature standard SCR, and dimeric sites provide the majority of reactivity at higher temperatures. For NO oxidation, dimeric sites are the active centers. NH3 oxidation, on the other hand, is catalyzed by sites with higher nuclearity.

Iron Loading Effects in Fe/SSZ-13 NH3-SCR Catalysts: Nature of the Fe Ions and Structure–Function Relationships

MoS2 and Ni-promoted MoS2 catalysts supported on γ-Al2O3, siliceous SBA-15, and Zr- and Ti-modified SBA-15 were explored for the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrodenitrogenation (HDN) of o-propylaniline (OPA). In all cases, OPA reacted preferentially via initial hydrogenation, and DBT was converted through direct sulfur removal. HDN and HDS activities of MoS2 catalysts are determined by the dispersion of the sulfide phase. Ni promotion increased its dispersion and activity for DBT HDS and also increased the rate of HDN via enhancing the rate of hydrogenation. On nonpromoted MoS2 catalysts, HDS was strongly inhibited by NH3, and the addition of Ni dramatically reduced this inhibiting effect. The conclusion is that HDS is proportional to the concentration of Mo and Ni on the edges of sulfide particles. In contrast, the direct hydrodenitrogenation of OPA occurs only on accessible Mo cations and, hence, decreases with increasing Ni substitution. The nature of the supp...

Effects of the Support on the Performance and Promotion of (Ni)MoS2 Catalysts for Simultaneous Hydrodenitrogenation and Hydrodesulfurization

Structural changes to Fe3+ cationic species in Fe-exchanged zeolite BEA during the selective catalytic reduction (SCR) of NOx with NH3 were probed by UV–vis spectroscopy. The distribution between Fe2+ and Fe3+ species was characterized by IR spectroscopy of adsorbed CO. Upon heating to 723 K, some of the Fe cations formed Fe–O–Fe bonds that underwent reversible structural transformation under NH3–SCR conditions. The in situ formed Fe oxide clusters could be dissociated to isolated Fe cations at 423 K, while at higher temperatures O-bridged Fe clusters were again formed. The structure of the Fe cluster is related to the Al distribution in the zeolite probed by Co2+ ion exchange. We propose here that two Fe cations bound within one six-membered ring containing an Al pair form hydroxylated dimeric Fe–O–Fe in the zeolite. This was supported by a structure simulation of a binuclear [HO-Fe(III)–O–Fe(III)–OH] model.

Jeongnam Kim

Papers

Effects of the Support on the Performance and Promotion of (Ni)MoS2 Catalysts for Simultaneous Hydrodenitrogenation and Hydrodesulfurization

Characterization of Fe-Exchanged BEA Zeolite Under NH3 Selective Catalytic Reduction Conditions