A characterization of Ln-Pd/SiO₂ (Ln=La, Ce, Sm, Eu, Gd and Yb): Correlation of surface chemistry with hydrogenolysis activity

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• 作者：Satyakrishna Jujjuri ; Errun Ding ; Sheldon G. Shore ; Mark A. Keane
• 关键词：Hydrodechlorination ; Pd/SiO₂ ; Ln-Pd/SiO₂ ; Lanthanide hydrides ; Chlorobenzene(s) ; Catalyst deactivation
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2007
• 出版时间：2 July 2007
• 年：2007
• 卷：272
• 期：1-2
• 页码：96-107
• 全文大小：1117 K

文摘

The gas phase hydrodechlorination (HDC) of chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB) and 1,3-dichlorobenzene (1,3-DCB) has been investigated over Pd/SiO₂ and a series of Ln-Pd/SiO₂ prepared from the organometallic precursor{(DMF)₁₀Ln₂[Pd(CN)₄]₃}_∞ where Ln = La, Ce, Sm, Eu, Gd and Yb; Pd loading = 5 % , w/w. Under identical reaction conditions, the following overall sequence of increasing initial fractional dechlorination has been established: Pd/SiO₂ < Yb-Pd/SiO₂ ≈ Sm-Pd/SiO₂ < Gd-Pd/SiO₂ < La-Pd/SiO₂ ≈ Ce-Pd/SiO₂ < Eu-Pd/SiO₂; reaction over Ln/SiO₂ resulted in a negligible conversion. HDC activity declined with time-on-stream but the Ln-Pd/SiO₂ catalysts maintained a significantly higher fractional HDC than Pd/SiO₂; loss of activity is attributed to deleterious HCl/surface interactions. The pre- and post- reaction catalyst samples have been characterized in terms of BET area, TPR, TEM, H₂ chemisorption/TPD, XRD and XPS analyses. When compared with Pd/SiO₂, Pd is present in the Ln-Pd/SiO₂ samples as much smaller particles, while the lanthanide component is finely dispersed over the surface, i.e. Ln is in intimate contact with Pd. The promotional effect of Ln in Ln-Pd/SiO₂ is attributed to a surface Pd/Ln synergism resulting in an enhancement of surface reactive hydrogen and a more effective CCl bond activation for hydrogenolytic attack. HDC performance is discussed in terms of surface composition, Pd particle size, Ln electronic structure and H₂ uptake/release dynamics.