Structure鈥揂ctivity Studies on Highly Active Palladium Hydrogenation Catalysts by X-ray Absorption Spectroscopy

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• 作者：Matthias Bauer ; Roland Schoch ; Lidong Shao ; Bingsen Zhang ; Axel Knop-Gericke ; Marc Willinger ; Robert Schl枚gl ; Detre Teschner
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：October 25, 2012
• 年：2012
• 卷：116
• 期：42
• 页码：22375-22385
• 全文大小：576K
• 年卷期：v.116,no.42(October 25, 2012)
• ISSN：1932-7455

文摘

Functionalized carbon nanotubes were used to produce Pd-based hydrogenation catalysts. Pd/CNT with small (1鈥? nm) Pd particles showed classical catalytic behavior in propyne hydrogenation, with high propene selectivity at moderate conversion levels and propane formation near full conversion. Pd/CNT with larger (15 nm) nanoparticles, however, was selective (88%) toward propene even at practically full propyne conversion. An additionally prepared Pd₂Ga/CNT catalyst exhibited even higher propene selectivity at full conversion. All of these materials were studied in situ by X-ray absorption spectroscopy at the Pd K-edge. Pd₂Ga/CNT was stable under all conditions examined without variation in XANES or in the derived EXAFS parameters. Both Pd/CNT samples formed 尾-hydride under hydrogen, as assessed from the calculated lattice expansion and the characteristic red shift of the XANES maxima. The minor spectroscopic difference between the monometallic catalysts observed at high propyne conversion suggests the decisive role of a Pd鈥揅 (subsurface C) contribution in the structure of larger Pd particles, being absent with ultrasmall nanoparticles. In general, all factors (intermetallic phase formation, subsurface C, etc.) that reduce the surface H coverage will give rise to enhanced partial hydrogenation selectivity of palladium when secondary alkene hydrogenation at late bed segments or diffusion issues in the pores are avoided.