Thermal Spreading As an Alternative for the Wet Impregnation Method: Advantages and Downsides in the Preparation of MoO3/SiO2−Al2O3 Metathesis Catalys

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• 作者：Damien P. Debecker ; Mariana Stoyanova ; Uwe Rodemerck ; Pierre Eloy ; Alexandre Lonard ; Bao-Lian Su ; Eric M. Gaigneaux
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：November 4, 2010
• 年：2010
• 卷：114
• 期：43
• 页码：18664-18673
• 全文大小：442K
• 年卷期：v.114,no.43(November 4, 2010)
• ISSN：1932-7455

文摘

Silica−alumina-supported MoO₃ catalysts are classically prepared via impregnation of the support with a molybdenum salt solution, usually ammonium heptamolybdate, and subsequent drying and calcination (three steps). The downsides of such a route for the synthesis of heterogeneous metathesis catalysts are linked to the limited control on the nature of the MoO_x stabilized at the surface, to the uneven distribution of the deposit in the pores of the support, and to the build up of inactive species that find their origin in the wet step of the preparation. In opposition, the direct thermal spreading of molybdenum oxide onto the support is a straightforward (one step) method involving no wet stage. It allows the conversion of bulk MoO₃ crystals to amorphous molybdate species dispersed at the surface of the silica−alumina support. This contribution shows that the catalysts obtained via both methods exhibit similar performances in the self-metathesis of propene to butene and ethene. However, based on XRD, XPS, Raman spectroscopy, ICP-AES, N₂ physisorption, TEM, and MAS-NMR spectroscopy, it is shown that the origin of active and inactive species in the two systems is different. Whereas the activity of wet-made catalysts is limited by the formation of bulky MoO₃ crystals and of aluminum molybdate, the performances of dry-made catalysts are limited by the incomplete spreading of MoO₃ nanocrystallites.