Nowadays, desulfurization of liquid fuels is inevitable because of strict environmental and industrial regulations on liquid fuels specifications. Hydrodesulfurization (HDS) technology has been used widely to produce fuels with ultralow sulfur content (S ≤ 10 ppm). However, this method is not effective enough for removing refractory sulfur compounds (e.g., benzothiophene, dibenzothiophene, and their derivatives). Consequently, alternative or supplementary desulfurization methods have been rapidly developed in recent years. The oxidative desulfurization (ODS) process is a promising method with high selectivity, low cost, mild reaction conditions, and high efficiency. In the past few decades, the ODS process of fuels by polyoxometalates (POMs) as catalysts have attracted considerable attention, resulting in different works have been published due to their strong acidity, fast and reversible multielectron redox properties, tunable redox properties, as well as thermal, hydrolytic, and oxidative stability. In this review, the removal of S-compounds from fuel oils is investigated via the ODS process using homogeneous and heterogeneous polyoxometalate catalysts. Moreover, the advantages and problems of each system are discussed. Various techniques for reducing their noticeable drawbacks are also presented. Finally, the regeneration of POM catalysts, as an important step in industrial applications, is examined.

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The development of adsorbents for gas desulfurization is highly essential to control sulfur dioxide emissions. In this article, CuO-modified SBA-15 and MOR-SBA-15 composite adsorbents were prepared by impregnation and post-grafting methods. As-prepared adsorbents were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and N2 adsorption–desorption methods. Furthermore, the adsorption desulfurization efficiency was investigated. The results proved that the impregnation method exhibited a remarkable dominance compared to the grafting method. The 8.7% CuO/MOR-SBA-15-imp adsorbent showed superior performance compared with other adsorbents in removing SO2 from the flue gas. Moreover, the 8.7%CuO/MOR-SBA-15-imp adsorbent illustrated an excellent regeneration for five cycles. The optimal condition for the flue gas desulfurization with the flow rate of 13 NL/h was 400 °C and a 200 mg adsorbent. Kinetic model studies showed that the model was pseudo-first order, and the amounts of activation energy for the 8.7% CuO/SBA-15-imp and 8.7% CuO/MOR-SBA-15-imp samples were 20.4 and 18.5 kJ/mol, respectively.

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