Thermal spreading as an alternative for the wet impregnation method: Advantages and downsides in the preparation of MoO3/SiO 2-Al2O3 metathesis catalysts

Damien P. Debecker, Mariana Stoyanova, Uwe Rodemerck, Pierre Eloy, Alexandre Léonard, Bao Lian Su, Eric M. Gaigneaux

Research output: Contribution to journalArticlepeer-review

Abstract

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 MoOx 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 MoO 3 crystals and of aluminum molybdate, the performances of dry-made catalysts are limited by the incomplete spreading of MoO3 nanocrystallites.

Original languageEnglish
Pages (from-to)18664-18673
Number of pages10
JournalJournal of Physical Chemistry C
Volume114
Issue number43
DOIs
Publication statusPublished - 4 Nov 2010

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