摘要：

Cyclopropane (CP) chemisorption on silica-molybdena catalysts photoreduced in CO was found to result in a sharp increase (by more than one order of magnitude at 293 K) of specific activities for propene metathesis. IR and UV-vis diffuse reflectance spectroscopic studies revealed that the promoting effect of CP treatment was associated with the formation of surface carbene species arising from CP interaction with low coordinated Mo 4+ ions produced by photoreduction of Mo 6+/SiO 2 in CO. Such carbones (MoCH 2) are found to be thermally stable in vacuo up to 650 – 700 K, oxygen resistant at 293 K and to react with water vapour at ~400K to yield CH 4. The IR data obtained showed fast reversible transformation of MoCH 2 to MoCD 2 after C 2D 4 admission. In addition to MoCH 2, the spectroscopic data indicate the formation of ethylene and propene π -complexes with Mo 4+ ions and Mo cyclobutanes during CP chemisorption. Ethylene adsorbed on Mo 4+ ions gave rise to π-complexes and possibly Mo-cyclopentane species. A general scheme for CP interaction with photoreduced Mo 4+/SiO 2 explaining all the spectroscopic data obtained, the composition of the thermally desorbed products and the promoting effect of CP chemisorption on metathesis is presented and discussed.

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