Supported metal oxide and other catalysts for ethane conversion: a review

Bañares, Miguel Á.

doi:10.1016/s0920-5861(99)00053-x

Cited by 367 publications

(238 citation statements)

References 212 publications

Supporting

Mentioning

227

Contrasting

Unclassified

Order By: Relevance

“…[28] The data could be fitted with a monomeric VO 4 Based on the results of XANES, Raman, UV/Vis, and ESR analyses, as presented in the Supporting Information, we tentatively assume that not all of the vanadium oxide clusters in 1V-Al-R are reduced. This would imply that a mixture of the original dehydrated four-fold coordinated vanadium and reduced octahedrally coordinated vanadium is present in the hydrogen-treated vanadium oxide catalyst.…”

Section: Resultsmentioning

confidence: 99%

“…An electron-donating substituent (NH 2 ) results in a higher AXAFS intensity than an electron-withdrawing substituent (COOH), and the peak centroid shifts to lower values of R for the electron-withdrawing substituent. [22,23] The influence of neighbouring atoms over a longer range has been demonstrated for Zn(OH) 4 2À ions in basic solution. The interaction between the zincate ion and surrounding hydrated cations causes dramatic changes in the AXAFS as a result of changes in the Zn À M distances and cation electronegativity.…”

Section: Introductionmentioning

confidence: 97%

“…[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.…”

Section: Introductionmentioning

confidence: 99%

“…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. Using Na 3 VO 4 and V 2 O 5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been determined; this led to a 50 % decrease in the AXAFS intensity and to an increase in the centroid position.…”

Section: Introductionmentioning

confidence: 99%

“…The distances of the V= O (1) and VÀO (2) coordinations of the VO 4 unit, as found in the EXAFS analysis, were used as input parameters for the Cerius 2 molecular modelling program. The coordination numbers and distances of the VÀO (3) and VÀAl (4) higher coordination shells, as found in the EXAFS analysis, were taken as structural constraints. Rotation of the VO 4 unit about the Al support ÀO (2) bond and bending of the VÀO (2) ÀAl support bond were the only operations performed to find a configuration that fitted the EXAFS data.…”

mentioning

confidence: 99%

See 4 more Smart Citations

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

Keller

Weckhuysen

Koningsberger

2007

Chemistry A European J

View full text Add to dashboard Cite

IntroductionMany parameters affect the catalytic properties of transition-metal oxide catalysts, for example, metal oxide loading, pre-treatment conditions, molecular structure, electronic structure, and the nature of the supporting oxide. [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.To study the effect of the support on the catalytic performance, one has to find a tool that is capable of probing the influence of the local environment (e.g., the support or promoters) on the properties of the catalytically active species, that is, a metal particle or metal oxide cluster. Metal-A C H T U N G T R E N N U N G (oxide)-support interactions can be ascribed to a structural (particle/cluster size and shape) effect, but can also have an electronic origin. For supported metal particles, the effect of the support on the catalytic properties has been determined by several techniques, for example, XPS, FT-IR analysis of adsorbed CO, and newly developed delta XANES and atomic XAFS (AXAFS) techniques. [8][9][10][11][12][13][14][15] In particular, the application of AXAFS has, in our opinion, led to a better understanding of metal-support interaction effects. [8,[15][16][17] AXAFS is sensitive to changes in the potential around the X-ray absorbing atom. The potential field around an atom is mainly determined by the first and second coordination spheres. O Grady et al. have shown for Pt/Ru alloys that the AXAFS intensity changes systematically with the composition of the alloy. [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. Using Na 3 VO 4 and V 2 O 5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been dete...

show abstract

Section: Resultsmentioning

confidence: 99%