Dynamic States of V 2 O 5 Supported on SnO 2 /SiO 2 and CeO 2 /SiO 2 Mixed-Oxide Catalysts during Methanol Oxidation (original) (raw)
1998, The Journal of Physical Chemistry B
A series of V 2 O 5 supported on the SnO 2 /SiO 2 and CeO 2 /SiO 2 mixed oxides were investigated during methanol oxidation by in situ Raman spectroscopy, and the catalytic properties of these catalysts were probed by methanol oxidation kinetic studies. The Raman studies revealed that tin oxide forms a surface SnO x overlayer on the silica surface owing to the absence of Raman features of the SnO 2 crystallite, but cerium oxide forms bulk CeO 2 particles on the silica surface. The impregnated vanadium oxide formed a surface vanadia overlayer on all the catalysts owing to the absence of V 2 O 5 crystallite Raman features. In situ Raman studies of the V 2 O 5 /SnO 2 /SiO 2 and V 2 O 5 /CeO 2 /SiO 2 catalysts during methanol oxidation indicate that the formation of the VO x-SnO x and VO x-CeO 2 interactions totally blocks the formation of surface V-OCH 3 groups, which are observed in the V 2 O 5 /SiO 2 catalysts. The interaction between the surface VO x and the surface SnO x overlayer on silica increases the methanol oxidation reactivity by 1-2 orders of magnitude relative to V 2 O 5 /SiO 2 , and partial interaction between the surface VO x and bulk CeO 2 particles increases the methanol oxidation reactivity by 0-1 order of magnitude relative to V 2 O 5 /SiO 2. Temperature programmed reduction (TPR) studies indicate that the reducibility of the surface vanadium oxide species is dependent on the reducibility of the specific oxide support and confirm the formation of the VO x-SnO x bonds for the V 2 O 5 /SnO 2 /SiO 2 catalyst and the formation of VO x-CeO 2 as well as VO x-SiO 2 bonds for the V 2 O 5 /CeO 2 /SiO 2 catalyst.
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