Curved nanostructures of unsupported and Al₂O₃-supported MoS₂ catalysts: Synthesis and HDS catalytic properties

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• 作者：Anabela Nogueira^a ; Raja Znaiguia^a ; Denis Uzio^b ; Pavel Afanasiev^a ; Gilles Berhault^a ; ^{Gilles.Berhault@ircelyon.univ-lyon1.fr}
• 关键词：Hydrodesulfurization ; MoS2 ; Bending ; Hydrogenation ; Fullerene-like
• 刊名：Applied Catalysis A ; General
• 出版年：2012
• 期刊代码：4_0926860x
• 类别：ch
• 出版时间：2 July, 2012
• 卷：429-430
• 期：Complete
• 页码：92-105
• 文件大小：1729 K

摘要

The active phase of hydrodesulfurization (HDS) catalysts is usually composed of MoS₂ slabs promoted by cobalt and/or nickel. Because of the anisotropic structure of molybdenum disulfide, the active sites are believed to be present only on the edges of the slabs, exhibiting dangling bonds. However, slabs of MoS₂-based industrial catalysts often exhibit disordered bent morphology which might generate strain effects creating new active sites. In order to evaluate a possible effect of bending MoS₂ slabs on HDS catalytic properties, synthesis of well-defined curved morphologies was carried out in the present study. Two different strategies were evaluated herein: acidification of ammonium tetrathiomolybdate, (NH₄)₂MoS₄ (ATM) in the presence of polyethyleneglycol or decomposition of ammonium thiodimolybdate, (NH₄)₂Mo₂S₁₂ (ATDM). The resulting amorphous sulfides, deposited or not on 纬-Al₂O₃, were then post-treated at 400 掳C or 750 掳C under N₂ or H₂ in the presence or not of H₂S. Cobalt promotion was also attempted on the final post-treated solids. The results show that the nature of the sulfur-containing precursor strongly influences the final morphology. Using ATM, the as-obtained nanospheres are formed of bundles of slabs while using ATDM, fullerenic-like MoS₂ particles are obtained after post-treatment at 750 掳C. These fullerenic-like particles exhibit non constant radius of curvature with flat regions separated by strongly localized distorted zones suggesting the formation of defect sites on basal planes. The possibility of promoting these systems by Co sustains the presence of such surface sites. XPS and TPR results also show a marked weakening of the metal-sulfur bond strength when compared to flat crystals. Finally, catalytic activities determined for the HDS of thiophene and the simultaneous hydrogenation (HYD) of toluene and isomerization of cyclohexane are rather noticeable despite the absence of conventional edge sites. Bending MoS₂ slabs therefore seems to lead to the creation of new active sites on basal planes with original catalytic properties.