Supported metal oxide based olefin metathesis catalysts (MoOx, WOx and ReOx) have been widely used in several megaton-scale industrial processes. Unfortunately, the activity of supported metal oxide catalysts is generally lower than organometallic catalysts by several orders of magnitude. Unlike the organometallic catalysts that have well-defined structures, supported metal oxides always contain a mixture of surface species with less than 1-2% of the total metal atoms contributing to the reaction. The small fraction of active species not only limits the catalytic performance of these oxide catalysts, but also acts as a barrier to unambiguous identification of the active site structures. We report that a simple pretreatment of MoO3/SiO2 and WO3/SiO2 leads to two to three orders of magnitude higher propylene metathesis activity (TOF of ~103/h). The performance of these catalysts is comparable with those of the well-defined organometallic catalysts. The catalyst can be easily regenerated. Furthermore, we have succeeded in identifying the active sites of MoO3/SiO2 through a combination of isotope tracing, UV resonance Raman spectroscopy, and atomic-resolution electron microscopy. The atomic-level understanding of the active site structure will advance the rational design of high performance oxide-based olefin metathesis catalysts.

Activation, regeneration, and active site identification of oxide-based olefin metathesis catalysts

251st National Meeting (2016)

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