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1s2p resonant inelastic X-ray scattering (RIXS) spectroscopy has been measured for a series of iron oxides, including octahedral and tetrahedral Fe(II) and Fe(III) systems. Their spectral shapes have been analyzed and explained using crystal-field multiplet simulations. The RIXS planes and the K-edge and L-edge X-ray absorption spectra related to these RIXS planes will be discussed with respect to their analytical opportunities. It is concluded that the full power and possibilities of 1s2p RIXS needs an overall resolution of 0.3 eV. This will yield a technique with more detailed information than K-edge and L-edge X-ray absorption combined, obtained in a single experiment. Another major advantage is that 1s2p RIXS involves only hard X-rays, and experiments under essentially any condition and on any system are feasible.

UV-vis spectroscopy was used in a combined in-situ UV-vis/XAFS spectroscopic setup to study the synchrotron radiation effect on aqueous homogeneous copper solutions. Two different systems were studied. In the first study, the focus was on a copper bipyridine-catalyzed oxidation of benzyl alcohol to benzaldehyde with 2,2,6,6- tetramethylpiperidinyl-l-oxy and base as cocatalysts. It was found that when the reaction mixture is exposed to the X-ray beam, the features present in the in-situ UV-vis spectrum develop differently compared to the situation when the reaction mixture is not exposed to the X-ray beam. Besides a temperature effect of the X-ray beam, both the UV-vis analysis and the XAFS analysis showed a reducing influence of the X-ray beam on the sample. To investigate this in more detail, we Studied a series of dilute aqueous copper solutions from different precursor salts, viz., Cu(NO3)(2).3H(2)O, CUSO4.5H(2)O, CuCl2, and CuBr2. It was found that the different aqueous copper solutions have different stabilities under the influence of the X-ray beam. Especially the solution from the CuCl2 precursor salt was found to be unstable and to be subjected to reduction. These examples illustrate the need for a second technique, such as in-situ UV-vis spectroscopy, to evaluate the effect of synchrotron radiation used to measure in-situ XAFS on catalytic systems.

The dimerization of 1,3-dienes (e.g. butadiene) with the addition of a protic nucleophile (e.g. methanol) yields 2,7-octadienyl ethers in the so-called telomerization reaction. This reaction is most efficiently catalyzed by homogeneous palladium complexes. The field has experienced a renaissance in recent years as many of the platform molecules that can be renewably obtained from biomass are well-suited to act as multifunctional nucleophiles in this reaction. In addition, the process adheres to many of the principles of green chemistry, given that the reaction is 100% atom efficient and produces little waste. The telomerization reaction thus provides a versatile route for the production of valuable bulk and specialty chemicals that are (at least partly) green and renewable. The use of various multifunctional substrates that can be obtained from biomass is covered in this review, as well as mechanistic aspects of the telomerization reaction.

X-ray absorption spectroscopy at the Cr K- and L-2,L-3-edges was used to study the assembling process of a heterogeneous Cr-based single-site catalyst. The starting point was a Phillips-type system with monochromate species anchored on a silica surface, which was first reduced to a variety of different surface Cr-II species. The reduced sample was modified with a 1,3,5-tribenzylhexahydro 1,3,5-triazine (TAC) ligand in the presence of CH2Cl2 as solvent to yield a heterogeneous single-site Cr-based catalyst active in the trimerization of ethylene. The molecular structure of the resultant catalytic material consists of distorted octahedral Cr-III species. The extended X-ray absorption fine-structure (EXAFS) spectroscopy fitting procedure in R space up to 2.5 angstrom showed that the synthesis leads to coordination with a TAC ligand. The fit also shows that it was possible to complete the six-fold environment around Cr-III with two oxygen atoms and one chloride ligand. This chloride ligand is formed in a redox process from the solvent and is responsible for the oxidation of surface Cr-II to Cr-III. The obtained geometry and the local environment of the surface complex are discussed in light of its homogeneous counterpart and confirm the single-site characteristics of the prepared catalytic material.

Electron energy-loss spectroscopy (EELS) in combination with scanning transmission electron microscopy ( STEM) reveals that the La enrichment at the surface of cerium-lanthanum solid solutions is an averaged effect and that segregation occurs in a mixed oxide phase. This separation occurs within a crystalline particle, where the dopant-rich phase is located at the surface of the dopant-deficient phase. The limiting structure appears to be a solid solution with a La fraction of x = 0.6 in the bulk and x = 0.75 at the surface. Up to a La fraction of 0.6, this phase will coexist with a lanthanum-type structure in different proportions depending on the dopant amount. STEM-EELS appears to be a powerful technique to clarify the existence of a multiphase system, and it shows that XRF, XPS, and XRD measure averaged results and do not show the phase complexity of the solids.

A CrAPO-5 molecular sieve has been investigated with X-ray absorption spectroscopy (EXAFS-XANES) as dehydrated material and after loading with water and ammonia to unravel the coordination geometries of Cr3+ in the framework of a microporous crystalline aluminophosphate, more particularly of the AFI-type. A comparison of the XANES data, a preedge analysis with crystal field multiplet calculations and EXAFS data, pointed toward the presence of framework Cr3+ which, on dehydration, takes on a distorted tetrahedral coordination state. Due to the 3d3 configuration of Cr3+, this unusual tetrahedral coordination environment strongly tends to transform into the more stable 6-fold coordination geometry by binding two extraframework water molecules during hydration. In the presence of ammonia, tetrahedral Cr3+ readily transforms into a 5-fold coordination geometry by binding one ammonia molecule. Therefore, depending on the environmental conditions, the Cr3+ ions can occur in a 4-, 5-, or 6-fold coordination. This observation underlines the flexibility of transition metal ions, such as Cr3+, to cope with unusual coordination geometries in inorganic hosts, making them interesting as potential active sites in heterogeneous catalysis. ispartof: Journal of Physical Chemistry B vol:110 issue:2 pages:716-722 ispartof: location:United States status: published

We present extended x-ray absorption fine structure (EXAFS) data at the La L2 edge in LaOCl that were recorded on the Lβ1 fluorescence line with an analyzer energy bandwidth of 1.3eV. We show that by taking advantage of the high-energy-resolution fluorescence detection (HERFD) it is possible to extend the energy range for L2 EXAFS analysis beyond the L1 edge if the sample is optically thin. The arguments presented here generally apply to fluorescence-detected absorption spectroscopy if the fluorescence lines are sufficiently separated in energy. Calculations using an atomic multiplet model show that intensity due to 2p4d multiple-electron excitations is reduced in HERFD spectra. The technique has the potential of considerably improving EXAFS analyses at low energies (

UV-vis spectroscopy was used in a combined in-situ UV-vis/XAFS spectroscopic setup to study the synchrotron radiation effect on aqueous homogeneous copper solutions. Two different systems were studied. In the first study, the focus was on a copper bipyridine-catalyzed oxidation of benzyl alcohol to benzaldehyde with 2,2,6,6- tetramethylpiperidinyl-l-oxy and base as cocatalysts. It was found that when the reaction mixture is exposed to the X-ray beam, the features present in the in-situ UV-vis spectrum develop differently compared to the situation when the reaction mixture is not exposed to the X-ray beam. Besides a temperature effect of the X-ray beam, both the UV-vis analysis and the XAFS analysis showed a reducing influence of the X-ray beam on the sample. To investigate this in more detail, we Studied a series of dilute aqueous copper solutions from different precursor salts, viz., Cu(NO3)(2).3H(2)O, CUSO4.5H(2)O, CuCl2, and CuBr2. It was found that the different aqueous copper solutions have different stabilities under the influence of the X-ray beam. Especially the solution from the CuCl2 precursor salt was found to be unstable and to be subjected to reduction. These examples illustrate the need for a second technique, such as in-situ UV-vis spectroscopy, to evaluate the effect of synchrotron radiation used to measure in-situ XAFS on catalytic systems.

The addition of small amounts of Mn to a Co/TiO2 catalyst affects the catalytic performance in the Fischer-Tropsch synthesis (FTS) by increasing the activity and suppressing the CH4 yield. These variations in the catalyst selectivity are due to Mn promotion effects that influence the final catalyst active site distribution, playing a role under reaction conditions. The use of STEM-EELS and XPS has provided more insight into the location of Mn as a function of the catalyst surface composition observed after the main preparation steps, that is, calcination and reduction. XPS shows that after calcination the catalysts contain mainly a Co3O4 phase, and that after 4 h of reduction in H-2 flow at 350 degrees C, a fair fraction of the Co3O4 is fully reduced to Coo. The STEM-EELS measurements reveal the existence of a clear Co-Mn association in the calcined catalyst, in which the Mn apparently forms a mixed oxidic phase with the Co particles and thus causes a decrease in the Co reducibility with respect to a Mn-free Co/TiO2 catalyst. The Mn tends to segregate over the TiO2 support after reduction, as indicated by the increase in the Mn/Co and Mn/Ti atomic ratios obtained from XPS. Hence, the Mn compounds migrate from the Co particles and are enriched at the surface of the TiO2 support during Co3O4 reduction to Coo. However, the STEM-EELS images obtained for the reduced catalyst reveal a remaining Co-Mn interaction, which presumably causes the promotion effect in FTS. (c) 2004 Elsevier Inc. All rights reserved.

STEM-EELS and EXAFS have been used to investigate the location and electronic state of Mn as promoter in TiO2-supported cobalt Fischer-Tropsch catalysts prepared by two different procedures. It was found that the extent of interaction between Mn and the active Co phase as well as the level of Mn dispersion over the TiO2 surface largely determine the enhancement of the selectivity in the Fischer-Tropsch synthesis at pressures of 1 bar. ispartof: Physical Chemistry Chemical Physics vol:7 issue:4 pages:568-572 ispartof: location:England status: published

In-situ soft X-ray absorption spectroscopy (XAS) has been applied to study the iron redox behavior in over-exchanged Fe/ZSM5. The Fe L-2,L-3 XAS and O K spectral shapes of the Fe/ZSM5 surface have been measured during heat treatments and reduction/oxidation cycles. Charge-transfer multiplet calculations provide a detailed understanding of the L-2,L-3 spectra of iron in Fe/ZSM5. The oxidized form of Fe/ZSM5 contains Fe-III ions in an octahedral surrounding, with a total crystal field splitting of similar to1.0 eV. This value is significantly smaller than that for Fe2O3, which is indicative of a much weaker Fe-O bonding. The reduced form of Fe/ZSM5 has Fell ions in a tetrahedral oxygen surrounding. The Fe L-2,L-3 spectra show that iron in calcined Fe/ZSM5 is reduced in 15 min to an average valence state of 2.65, under 10 mbar of pure helium at room temperature. This value has a relative uncertainty on the order of 0.01. Heating in helium up to 350 degreesC under the same pressure further reduces the iron valence to 2.15. The oxygen spectra show that the autoreduction is accompanied by a loss of molecular oxygen and water. Reoxidation with 5% O-2 in helium yields a valence of >2.90 after 10 min.

The oxidation and reduction behaviour of calcined over-exchanged Fe/ZSM5 has been studied using soft X-ray absorption by measuring the average iron valence under (2 mbar) helium, oxygen and deNOx (HC-SCR) conditions between room temperature and 350 degreesC. The results ( probing depth of approximately 4 nm) show that Fe/ZSM5 is an extremely flexible redox system. The calcination procedure (severe calcination: heating rate 5 degreesC min(-1), as normally used in the literature; mild calcination: heating rate 0.5 degreesC min(-1)) is proven to be important to optimise the reducibility of iron. Upon mild calcination Fe/ZSM5 has an average valence of 2.9 under oxygen (5% in helium), of 2.5 under pure helium at room temperature (RT), and of 2.1 under pure helium at 350 degreesC. Upon severe calcination Fe/ZSM5 shows higher average valences, in agreement with the assumption that part of the iron in this sample is positioned in small iron-oxide nanoparticles at the outer surface of the zeolite crystals. During heating in helium, the valence reaches a minimum value before slightly rising again (re-oxidation) when the temperature is kept constant. It is also found that the X-ray irradiation is able to affect the average valence by values up to 0.10. This study confirms that iron in 'over-exchanged' Fe/ ZSM5 consists dominantly of highly reactive iron complexes, where the iron is ( distorted) octahedral Fe-III in the oxidised state. The implications for the reaction mechanism for the N2O decomposition and the nature of the alpha-oxygen sites are discussed, in relation to recent developments in the understanding of iron non-heme enzymes.