On the Nature of Surface Vanadium Oxide Species on Carbons

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• 作者：M. Olga Guerrero-P茅rez ; Juana M. Rosas ; Ricardo L贸pez-Medina ; Miguel A. Ba帽ares ; Jos茅 Rodr铆guez-Mirasol ; Tom谩s Cordero
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：September 27, 2012
• 年：2012
• 卷：116
• 期：38
• 页码：20396-20403
• 全文大小：383K
• 年卷期：v.116,no.38(September 27, 2012)
• ISSN：1932-7455

文摘

Vanadium is a key component for selective and environmental catalysts. Supported vanadium oxide catalysts find many industrial applications for selective oxidation, ammoxidation, and reduction reactions for bulk and environmental processes. The properties of molecularly dispersed vanadium oxide species depend strongly on the nature of the support. Carbon materials are a particularly valuable kind of catalytic support (Rodrı́guez-Reinoso, F. Carbon1998, 36, 159), especially activated carbons prepared from biomass waste valorization, which are a very useful and economical material. In addition, if the carbon material presents phosphorus groups at its surface, as have been reported previously in the literature, then this material would be made resistant under oxidizing environments. Thus, this activated carbon is a very useful material for catalytic applications. This work provides molecular information about the nature of vanadium oxide species dispersed on activated carbon supports. As far as we know, there is little information available on the nature of surface vanadium species on carbons. Isolated monovanadates on an activated carbon can be identified by a Raman band close to 1020 cm^鈥? at low vanadium oxide coverage under dehydrated conditions. This Raman band redshifts upon hydration and is characteristic of the stretching mode of the V鈺怬 bond on molecularly dispersed vanadium oxide species. The Raman band of the V鈺怬 mode shifts from 1020 to 1024 cm^鈥? as the vanadium coverage increases, which must be due to an increasing polymerization of surface VO_x structures. The crystalline V₂O₅ phase appears when vanadia loading exceeds the dispersion limit loading on the support (typically known as the 鈥渕onolayer鈥?coverage), and such critical loading is reached at ca. 4 vanadium atoms per nm² of activated carbon support. To the best of our knowledge, the Raman bands of molecularly dispersed VO_x species on a carbon support under controlled environments are described for the first time.