Sulfur adsorption and sulfidation of transition metal carbides as hydrotreating catalysts

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• 作者：Ping Liu ; José ; A. Rodriguez and James T. Muckerman
• 关键词：Sulfur adsorption ; Sulfidation ; Density functional theory ; Metal carbide ; Nanocrystal ; Metcar
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：239
• 期：1-2
• 页码：116-124
• 全文大小：526 K

文摘

The formation of MoS_xC_y compounds has been observed on/in the surface of molybdenum-sulfide catalysts during the hydrodesulfurization (HDS) process, and it is a major factor for determining the activity of molybdenum-carbide catalysts. Density functional theory (DFT) was employed to investigate the adsorption of sulfur and sulfidation of transition metal carbides from groups 4–6 in the periodic table, including extended surfaces [MC(0 0 1) (M = Ti, V, Mo, Ta)], nanocrystals [M₁₄C₁₃ (M = Ti, V, Mo)] and metcar [M₈C₁₂ (M = Ti, V, Mo)] nanoparticles. It was found that with increasing carbon/metal ratio, the reactivity of the metal carbides towards sulfur decreased in the sequence: Mo₂C > M₁₄C₁₃, M₈C₁₂ > MC(0 0 1). In terms of sulfidation, M₈C₁₂ and MC(0 0 1) display a stronger resistance than M₁₄C₁₃. The presence of corner or edge sites in the M₁₄C₁₃ nanocrystal favors the formation of MoS_xC_y compounds. Following Sabatier's principle, our results suggest that flat MC(0 0 1) surfaces are too inert to catalyze HDS reactions, while M₁₄C₁₃ is too active to resist the sulfidation that leads to degradation of the carbides. For reactions involving sulfur and sulfur-containing molecules, nanoparticles adopting the special geometry of metcars should display a better catalytic activity than the corresponding bulk materials and carbide nanoparticles that have a cubic-based structure like nanocrystals. Indeed, DFT calculations indicate that Ti₈C₁₂ and Mo₈C₁₂ are good catalysts for the HDS of thiophene.