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1,467 results on '"Koningsberger, D.C."'

8. The nature of the Pt-H bonding for strongly and weakly bonded hydrogen on platinum. A XAFS spectroscopy study of the Pt-H antibonding shaperesonance and Pt-H EXAFS

Author

Oudenhuijzen, M.K., Bitter, J.H., Koningsberger, D.C., Yu, J.Y., Mao, S.Z., Zhang, L., and Miao, X.J.

Subjects
Extended X-ray absorption fine structure -- Usage, Platinum -- Chemical properties, Platinum -- Research, Hydrogen -- Chemical properties, Hydrogen -- Research, Adsorption -- Analysis, Chemicals, plastics and rubber industries
Abstract

Pt-H EXAFS in the presence and absence of hydrogen was used to gauge the nature of hydrogen adsorbed on Al(sub 2)O(sub 3) supported Pt-H particles. The Pt-H bond length is longer for weakly adsorbed hydrogen compared to strongly adsorbed hydrogen.

Published
2001

10. Al K-edge near-edge X-ray absorption fine structure (NEXAFS) study on the coordination structure of aluminum in minerals and Y zeolites

Author

Bokhoven, J.A. van, Sambe. H., Ramaker, D.E., and Koningsberger, D.C.

Subjects
Aluminum -- Research, Chemistry, Physical and theoretical -- Research, Zeolites -- Research, Chemicals, plastics and rubber industries
Abstract

Issues concerning the use of near-edge X-ray absorption fine structure and X-ray absorption spectroscopy to study the structure of aluminium in minerals and Y zeolites are discussed.

Published
1999

16. Gamma-Al2O3-Supported Re-Pt cluster catalyst prepared from [Re2Pt(CO)12]: characterization by extended X-ray absorption fine structure spectroscopy and catalysis of methylcyclohexane dehydrogenation

Author

Fung, A.S., Kelley, M.J., Koningsberger, D.C., and Gates, B.C.

Subjects
Dehydrogenation -- Analysis, Cyclic compounds -- Analysis, Chemistry
Abstract

Extended X-ray absorption fine structure (EXAFS) spectroscopic data indicated that the supported bimetallic clusters have simple structures that can qualify the compounds as nearly molecular in character. The catalyst derived from [Re2Pt(CO)12] consists of an oxophilic metal and a noble metal. The oxophilic metal has shown to have contributed to the stability of the compound.

Published
1997

21. Structure and nature of the metal-support interface: characterization of iridium clusters on magnesium oxide by extended X-ray absorption fine structure spectroscopy

Author

Zon, F.B.M. Van, Maloney, S.D., Gates, B.C., and Koningsberger D.C.

Subjects
Surface chemistry -- Analysis, Iridium -- Research, Magnesium oxide -- Analysis, Extended X-ray absorption fine structure -- Observations, Catalysts -- Analysis, Chemistry
Abstract

Metal-support interface in catalysts containing extremely tiny Ir clusters of almost uniform nuclearity on the surface of MgO powder is analyzed using x-ray absorption spectroscopy. These clusters are simple supported metals. Metal-oxygen distance of about 2.6 angstroms is usually typical in metal particles and clusters supported on metal oxides and zeolites. Metal atoms interacting with oxygen of the support with hydrogen present at the interface are responsible for the long distance.

Published
1993

24. Structurally simple supported platinum clusters prepared from (Pt15 CO 30)2- on magnesium oxide

Author

Chang, J.R., Koningsberger, D.C., and Gates, B.C.

Subjects
Platinum compounds -- Research, Magnesium oxide -- Research, X-ray spectroscopy -- Usage, Infrared spectroscopy -- Research, Chemistry
Abstract

The MgO adsorption of Na2PtCl6 has resulted in the formation of (Pt15 CO 30)2- on the surface of the MgO powder via surface-mediated synthesis. The resulting Pt cluster exhibits bridging CO ligands that are more reactive than terminal CO ligands. Decarbonylation of the Pt cluster does not affect the trigonal prismatic framework structure. However, subsequent recarbonylation results in the elimination of the original Pt cluster forming nonuniform hemispherical structures.

Published
1992

49. Changes in structural and electronic properties of the zeolite framework induced by extraframework Al and La in H-USY and La(x)NaY: A (super 29)Si and (super 27)Al MAS NMR and (super 27)Al MQ MAS NMR study

Author

Bokhoven, J.A. van, Roest, A.L., Koningsberger, D.C., Miller, J.T., Nachtegaal, G.H., and Kentgens, A.P.M.

Subjects
Silicon -- Research, Silicon -- Electric properties, Zeolites -- Research, Zeolites -- Electric properties, Chemistry, Physical and theoretical -- Research, Chemicals, plastics and rubber industries
Abstract

A (super 27)Al 3Q magic angle spinning (MAS), a quantitative (super 27)Al MAS, and a (super 29)Si MAS NMR study is carried out on La(x)NaY and H-USY. The (super 29)Si MAS and (super 27)Al MAS NMR results obtained at high fields (14.1 T) and fast MAS up to 27 kHz made a quantitative assignment possible of the framework and nonframework Al coordinations.

Published
2000

50. Hydration effects on the molecular structure of silica-supported vanadium oxide catalysts: A combined IR, Raman, UV–vis and EXAFS study

Author

Keller, D.E., Visser, T., Soulimani, F., Koningsberger, D.C., Weckhuysen, B.M., Heterogene katalyse en materialen, Heterogene katalyse en oppervlakteonderzoek, Katalyse en spectroscopie, and Dep Scheikunde

Abstract

The effect of hydration on the molecular structure of silica-supported vanadium oxide catalysts with loadings of 1–16 wt.% V has been systematically investigated by infrared, Raman, UV–vis and EXAFS spectroscopy. IR and Raman spectra recorded during hydration revealed the formation of V–OH groups, characterized by a band at 3660 cm−1. Hydroxylation was found to start instantaneously upon exposure to traces of water, reflecting a very high sensitivity of the supported vanadium oxide catalysts for H2O. Further hydration resulted in the appearance of a V–O–V vibration band located around 700 cm−1 pointing to the formation of di- or polymeric species. EXAFS analysis at 77 K indicated structural changes as the oxygen coordination changed from four to five. Moreover, a VV contribution was detected for the hydrated species. The IR, Raman and UV–vis data suggested a pyramidal anchoring of the dehydrated VOx species, whereas, the EXAFS data pointed to the presence of single V–O–Si bonded VOx species. This difference is attributed to water condensation effects at 77 K during EXAFS acquisition, resulting in a partial re-hydroxylation of the dehydrated samples, as confirmed by complementary IR and Raman analysis. Combining the results of this study with data from our previous studies [D.E. Keller, F.M.F. de Groot, D.C. Koningsberger, B.M. Weckhuysen, J. Phys. Chem. B 109 (2005) 10223; D.E. Keller, D.C. Koningsberger, B.M. Weckhuysen, J. Phys. Chem. B 110 (2006) 14313] as well as literature led to a reaction scheme in which a monomeric VOx species anchored by three Si–O–V bonds to the silica support (pyramidal-type structure) is transformed into a monomeric VOx species anchored by one Si–O–V bond (umbrella-type structure) by partial hydration of the catalyst material. This results in the formation of both V–O–H and Si–O–H bonds. At higher water pressures, larger vanadium oxide clusters are formed due to full hydration of the catalyst surface and a de-attachment of the vanadium oxide from the support surface. The results of this study provide evidence, that an umbrella-type structure (i.e., Si–O–VO(OH)2) could be present under catalytic conditions where H2O is a reaction product (e.g., partial oxidation of methanol to formaldehyde and oxidative dehydrogenation of alkanes). In other words, both the pyramidal ((Si–O)3–VO) and the umbrella (Si–O–VO(OH)2) model can exist at a support surface, their relative ratio depending on the hydration degree of the catalyst material. This study also illustrates that a corroborative characterization requires the use of multiple spectroscopic techniques applied at the same samples under almost identical measuring conditions.

Published
2007

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