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Formation of MoCH2 carbene complex on the surface of photoreduced silica—molybdena catalyst treated with 1,3,5-cycloheptatriene

1992; Science Press; Volume: 72; Issue: 1 Linguagem: Inglês

10.1016/0304-5102(92)80035-f

1873-3131

K.A. Vikulov, B.N. Shelhnov, V.B. Kazansky,

Advanced Chemical Physics Studies

The interaction of 1,3,5-cycloheptatriene (CHT) with surface Mo4+ ions produced by preliminary photoreduction of Mo6+/SiO2 catalyst in carbon monoxide was investigated. It was found that CHT chemisorption at room temperature followed by heating the catalyst at T⩾ 150 °C resulted in the formation of surface carbenes MoCH2, which were identified by their IR and UVVis spectra. CHT decomposition to MoCH2 and benzene at elevated temperatures was shown to be accompanied by a variety of side reactions. The specific activities of photoreduced Mo4/SiO2 for propene metathesis increased by a factor of 4–5 as a result of CHT treatment. A general scheme for CHT interaction with surface Mo4+ ions is discussed. MoCH2 concentration for CHT-treated catalysts was found to be approximately one order of magnitude lower than that produced by cyclopropane chemisorption on photoreduced Mo4+/SiO2.