Synthesis and Characterization of Ordered Mesoporous Silica Pillared Clay with HPW Heteropoly Acid Encapsulated into the Framework and Its Catalytic Performance for Deep Oxidative Desulfurization of Fuels

Abstract

Because of the increasing environmental concern and legal requirements, it has been an urgent subject to find new processes for ultra-deep desulfurization of fuel oils. The conventional hydrodesulfurization (HDS) technique has some inherent problems in treating sulfur-containing aromatic hydrocarbon compounds, such as dibenzothiophene (DBT) and its derivatives. Thus, a large number of non-HDS processes, such as adsorption, extraction, oxidation, precipitation and bio-processes have been explored [1-7]. Among these methods, catalytic oxidative desulfurization (ODS) combined with extraction is regarded as the most promising and economical process [8-11]. The ODS process has been studied in various systems, including oxidant H2O2 with inorganic acids [12], organic acids [13-15], TS-1 [16], and heteropoly acids (HPA) catalysts [17-19]. HPA catalysts, especially those having the Keggin structure, have been determined to be very effective for the oxidation of sulfurcontaining compounds in a liquid-liquid two-phase system. However, the separation and recovery of the catalysts are very difficult. For these reasons, the stable and water-tolerant solid acid catalysts have been developed. Li et al. [20], Lu et al. [21], and Gao et al. [22] reported [(C18H37)2N(CH3)2]3[PW12O40], [C18H37N(CH3)3]4[H2NaPW10O36], and Q[W(O)(O2)2(C5H4NCO2)] (Q=(C4H9)4N, [(CH3)3N(C18H37)] and [(C18H37)2N(CH3)2]) catalysts, respectively. Over these catalysts, DBT and its derivatives can be selectively oxidized into their corresponding sulfones using H2O2 as the oxidant in diesel oil. The surfactant-type catalysts provided a new process for deep ODS. However, the double long carbon chains of quaternary ammonium surfactant used in their system are very expensive. In our previous works, monovacant lacunary Keggin-type polyoxometalate was introduced into mesoporous silica structure and showed high oxidation activity for ODS [23]. Furthermore, we recently prepared a series of ordered mesoporous clay materials known as silica pillared clay (SPC) materials and metal ion doped SPC materials [24-29]. These