Dynamic behavior of supported vanadia catalysts in the selective oxidation of ethane

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

“…Raman spectrum (f) corresponds to 2.7 wt% VO x /SBA-15 after dehydration. It is dominated by a V=O stretchingband at 1040 cm -1 , which has been assigned to vanadium in a tetrahedral coordination [15,[17][18][19][20]. No V 2 O 5 -related bands (see spectrum (g) for comparison) were observed demonstrating the highly dispersed state of the anchored vanadium oxide species.…”

“…Vanadium oxides supported on silica exhibit high activity and selectivity for a number of model oxidation reactions, such as the partial oxidation of methane [10,11], methanol oxidation to formaldehyde [8,[12][13][14], and the oxidative dehydrogenation of ethane to ethylene [15]. To understand the correlation between structural and catalytic properties of dispersed vanadia, various techniques including infrared [16-18a,18b], Raman [19][20][21][22][23], UV-visible [16,17,20,24,25], solid-state 51 V NMR [21], and X-ray absorption spectroscopy [18,26] have been used.…”

Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

“…[1][2][3][4][5][6][7] Various researchers have investigated the activities and selectivities of metal oxide catalysts. However, little is known about the parameters that are truly responsible for the catalytic action of transition-metal oxides.…”

“…[18] Thus, when the number of Ru atoms around a Pt atom increases, the intensity of the FT AXAFS peak increases and the peak centroid shifts to lower values of R. Comparison of these effects with the effects observed for a Pt electrode as a function of the applied voltage suggests that the first coordination shell of the Pt in the Pt/Ru alloy influences the electronic properties (inter-A C H T U N G T R E N N U N G atomic potential) of the Pt atom. [18,19] The effect of changes in the coordination around the absorber atom has been further illustrated for Pt by van Dorssen et al, who compared the AXAFS of a Pt foil with that of bulk Na 2 Pt(OH) 6 . The AXAFS intensity was found to be significantly higher in the Abstract: The influence of changes in coordination number, interatomic distances, and oxidation state on the intensity and centroid position of the Fourier transform (FT) of the atomic X-ray absorption fine structure (AXAFS) peak of vanadium oxide bulk model compounds and aluminasupported vanadium oxide clusters has been investigated.…”

“…Keywords: AXAFS spectroscopy · metal-support interactions · solidstate structures · supported catalysts · vanadium oxides case of Na 2 Pt(OH) 6 and the peak position was shifted to lower values of R. The increase in intensity is due to the fact that the Pt À O bond length in Na 2 Pt(OH) 6 is shorter than the PtÀPt bond length in the foil, which results in more interaction between the Pt absorber atom and the scatterer oxygen atoms. [20] The influence of bond length on the position and intensity of the AXAFS peak has been thoroughly discussed by Wende et al [21] They showed that for oxygen atoms on a Cu surface, a shorter Cu À O distance caused the AXAFS peak to appear at lower values of R with increased intensity.…”