Active Sites in Olefin Metathesis over Supported Molybdena Catalysts

Abstract

Metathesis of propene to ethene and 2-butenes was studied over a series of MoO x /SBA-15 catalysts (molybdenum oxide supported on mesoporous silica SBA-15; Mo loading 2.1~13.3 wt%, apparent Mo surface density 0.2~2.5 nm -2

Room-Temperature Metathesis of Ethylene with 2-Butene to Propene Over MoOx-Based Catalysts: Mixed Oxides as Perspective Support Materials

“…Redox properties of MoO x might play a crucial role due to the following reason. It is generally accepted that Mo = CHR carbenes are active sites for olefin metathesis [7,13,28,29]. Such sites are assumed to be created through in situ activation of Mo 6+ O x by olefin molecule into Mo 4+ O x−1 followed by oxidative addition of another olefin molecule (Fig.…”

“…Isolated di-oxo or oligomeric mono-oxo supported MoO x show high activity for propene production, while crystalline MoO 3 is not active [10,11]. The influence of surface acidity on the activity of Mo-based catalysts was investigated in several independent works [9,[12][13][14]. Apparently, Brønsted acidic sites in close vicinity to MoO x species are relevant for high propene production at temperatures above 100 °C.…”

“…Apparently, Brønsted acidic sites in close vicinity to MoO x species are relevant for high propene production at temperatures above 100 °C. The activity can also be enhanced after thermal catalyst pretreatment in inert gas [15], propene, ethylene, methane [16], methanol [13] or after photoreductive treatment in CO or H 2 . [17] The influence of co-catalysts such as CaO, Al 2 O 3 or SiO 2 -Al 2 O 3 on the metathesis of ethylene and 2-butene to propene over MoO x /Al x Si y O z was investigated by Goelden et al [8].…”

MoO3 on zeolites MCM-22, MCM-56 and 2D-MFI as catalysts for 1-octene metathesis

“…Their catalytic activity depends on many factors, especially on Mo loading, support acidity, and pre-reaction activations. Surface isolated MoO 4 tetrahedra were proved as the main precursors of the catalytic species [ 6 – 7 ], thus the perfect dispersion of MoO 3 on the surface is a crucial precondition for a high catalytic activity. The mechanisms of transformation of these precursors to the surface Mo carbenes as real catalytically active species has been suggested [ 6 – 7 ].…”

“…Surface isolated MoO 4 tetrahedra were proved as the main precursors of the catalytic species [ 6 – 7 ], thus the perfect dispersion of MoO 3 on the surface is a crucial precondition for a high catalytic activity. The mechanisms of transformation of these precursors to the surface Mo carbenes as real catalytically active species has been suggested [ 6 – 7 ]. The replacement of ordinary silicas for mesoporous molecular sieves SBA-15 or MCM-41 increased the catalyst activity substantially, which allowed performing the metathesis of long chain olefins under mild reaction conditions [ 8 – 10 ].…”