It has previously been shown that there are many benefits to be obtained in combining several techniques in one in situ set-up to study chemical processes in action. Many of these combined set-ups make use of two techniques, but in some cases it is possible and useful to combine even more. A set-up has recently been developed that combines three X-ray-based techniques, small- and wide-angle X-ray scattering (SAXS/WAXS) and quick-scanning EXAFS (QEXAFS), for the study of dynamical chemical processes. The set-up is able to probe the same part of the sample during the synthesis process and is thus able to follow changes at the nanometre to micrometre scale during, for example, materials self-assembly, with a time resolution of the order of a few minutes. The practicality of this kind of experiment has been illustrated by studying zeotype crystallization processes and revealed important new insights into the interplay of the various stages of ZnAPO-34 formation. The flexibility of this set-up for studying other processes and for incorporating other additional non-X-ray-based experimental techniques has also been explored and demonstrated for studying the stability/activity of iron molybdate catalysts for the anaerobic decomposition of methanol.

The potential of combined operando UV-Vis/Raman/XAFS has been explored by studying the active site and deactivation mechanism of silica-and alumina-supported molybdenum oxide catalysts under propane dehydrogenation conditions.Ideally scientists would like to take real-time spectra inside a catalytic reactor when a catalytic process is operating, giving them detailed insight into the working principles of the catalytic material. 1 On this basis, it would then be possible to improve upon existing catalyst formulations or design completely new ones, which are more active and/or selective. Such rational catalyst design is still a dream since the experimental tools available to study the active catalyst do not yet provide sufficient insight. In this respect, it is advantageous to look on catalytic systems from different perspectives by making use of multiple characterisation techniques. In recent years, many attempts have been made to combine multiple spectroscopic techniques into one experimental set-up. The following combinations of two spectroscopic techniques have been recently reported for studying heterogeneous catalysts in action: EPR/UV-Vis, NMR/UV-Vis, XAFS/IR, UV-Vis/Raman and IR/UV-Vis. [2][3][4][5][6][7] Here, we describe a newly developed and powerful operando set-up to measure combined energy-dispersive (ED)-XAFS, UVVis and Raman to study a working catalytic solid. To our best knowledge, this is the first device which couples three spectroscopic techniques in one reactor, focuses on the same spot of a metal oxide catalyst under true reaction conditions and is capable of delivering sub second time resolution. A scheme of the set-up is given in Fig. 1. Further details are given in the ESI.{The operando device developed is widely applicable in the field of heterogeneous catalysis and its potential has been explored for the dehydrogenation of propane (5% in He) over supported Mo catalysts which have shown potential for alkane activation. 8,9 We have studied 13 wt% Mo/Al 2 O 3 and Mo/SiO 2 catalysts during successive propane dehydrogenation cycles at 550 uC. The three techniques are sensitive to changes in the oxidation/coordination states of Mo allowing us to obtain complementary information on the catalysts behaviour during dehydrogenation and regeneration. The set-up allows us to discriminate between the dynamics of both catalysts under reaction conditions and to identify the possible active site and deactivation pathways. Also the complementary aspects of this setup are demonstrated by showing how the catalyst undergoes changes which cannot be followed using one of the techniques alone and how it is possible to obtain quantitative Raman information without the use of an internal standard. Fig. 2 shows data collected using the three techniques during the first propane dehydrogenation cycle (PC1) for Mo/SiO 2 . The initial features observed in the spectra included a distinct 1s-4d pre-edge feature at 20002 eV in the ED-XANES, a strong LMCT band at ca. 350 nm in the UV-Vis and Raman bands at 992 (nMoLO), 82...

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The metal particle size and structure of the metal-support interface of platinum supported on Vulcan XC-72 (a commercial catalyst used in platinum fuel-cell electrodes) and on carbon nanofibers (CNF) have been determined with extended X-ray absorption fine structure spectroscopy (EXAFS). The CNF-supported Pt catalysts were synthesized using a homogeneous deposition precipitation (HDP) method. The amount of acidic oxygen groups on the CNF surface was modified by treatment in an inert atmosphere at different temperatures. The average first shell Pt-Pt coordination number (∼5.5) detected in Pt/CNF is much smaller than for Pt/ Vulcan XC-72 (∼8.2). The presence of oxygen-containing groups in the CNF support most probably leads to the stabilization of small Pt particles on the CNF support. A prominent interaction between the metal particles and the support atoms was detected on both kinds of catalysts, which confirms that the metal is in direct contact with the carbon support atoms. After reduction, a long metal-carbon distance around 2.62 Å was detected in both Pt/Vulcan XC-72 and Pt/CNF. After evacuation of Pt/CNF at higher temperatures, the distance between support and interfacial metal atoms decreased to 2.02 Å. Therefore, the long metal-carbon support distance is ascribed to the presence of atomic chemisorbed hydrogen in the interface between the Pt particles and the carbon support. According to the number of interfacial Pt-C bonds (four), the platinum particles supported on CNF are proposed to be in contact with a prismatic surface of the carbon support, on which oxygen groups have more stable bonds with carbon atoms. Six Pt-C bonds could be detected in the metal-support interface of Pt/Vulcan XC-72 with an even longer carbon shell at 3.62 Å, indicating that the metal particles are located on a more carbon-rich surface. This supports a structural model in which the platinum metal particles are epitaxially grown on the (0001) basal surface plane of carbon graphite.

Dehydrogenation promoters greatly enhance the performance of SiO 2 −MgO catalysts in the Lebedev process. Here, the effect of preparation method and order of addition of Cu on the structure and performance of Cupromoted SiO 2 −MgO materials is detailed. Addition of Cu to MgO via incipient wetness impregnation (IWI) or coprecipitation (CP) prior to wet-kneading with SiO 2 gave similar butadiene yields (∼40%) as when Cu was added to the already wet-kneaded catalyst. In contrast, the catalyst prepared by impregnation of Cu on SiO 2 first proved to be the worst catalyst of the series. TEM, XRD, and XPS analyses suggested that, for all catalyst materials, Cu 2+ forms a solid solution with MgO. This was confirmed by UV−vis, XANES, and EXAFS data, with Cu being found in a distorted octahedral geometry. As a result, the acid−base properties, as determined by Pyridine-and CDCl 3 −IR as well as NH 3 -TPD, are modified, contributing to the improved performance. Operando XANES and EXAFS studies of the evolution of the copper species showed that Cu 2+ , the only species initially present, is extensively reduced to a mixture of Cu 0 and Cu + , leaving only a limited amount of unreduced Cu 2+ . This formation of Cu 0 is the result of the reducing environment of the Lebedev process and is thought to be mainly responsible for the improved performance of the Cu-promoted catalysts.

The nature of the active Ti species in TiCl 3 -doped NaAlH 4 , a promising hydrogen storage material, was studied as a function of the desorption temperature with Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, Ti K-edge X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray diffraction (XRD). In the freshly prepared sample, Ti was amorphous and surrounded by 4.8 Al atoms divided between two shells at 2.71 and 2.89 Å. In the next shell, 1.9 Ti atoms were detected at 3.52 Å. It was concluded that 30% of Ti was incorporated into the surface of Al crystallites and 70% of Ti occupied interstitials in the NaAlH 4 lattice, possibly forming trimeric, triangular Ti entities. After hydrogen desorption at 125°C, NaAlH 4 decomposed and the Ti-Al coordination number increased from 4.8 to 8.5. We propose that all Ti is incorporated into the surface layer of the formed Al. After the material was heated to 225°C, the local structure of Ti, as inferred from EXAFS and XANES spectroscopy, was identical to the local structure of a TiAl 3 alloy. However, the formed alloy was amorphous and was only detected in XRD by an increase of the background intensity around the Al diffraction. These so-called "TiAl 3 clusters" agglomerated in the heat treatment to 475°C, forming crystalline TiAl 3 . Earlier work has shown that increasing the desorption temperature of NaAlH 4 lowers the absorption rate and capacity of hydrogen in the next step. Thus, by comparing our results with absorption properties published in the literature on similar samples, we could rank the activity of the Ti for hydrogen absorption as Ti in the Al surface > TiAl 3 cluster > crystalline TiAl 3 , therewith indicating that Ti incorporated into the surface of Al is the most active for the absorption of hydrogen.

, and Ba 2+ ) cations have been used as model systems to investigate the effect of promotor elements in the oxidation of CO in excess oxygen. Time-resolved infrared spectroscopy measurements allowed us to study the temperatureprogrammed desorption of CO from supported Pt nanoparticles to monitor the electronic changes in the local environment of adsorbed CO. It was found that the red shift of the linear Pt-coordinated CtO vibration compared to that of gas-phase CO increases with an increasing cation radius-to-charge ratio. In addition, a systematic shift from linear (L) to bridge (B) bonded CtO was observed for decreasing Lewis acidity, as expressed by the Kamlet-Taft parameter R. A decreasing R results in an increasing electron charge on the framework oxygen atoms and therefore an increasing electron charge on the supported Pt nanoparticles. This observation was confirmed with X-ray absorption spectroscopy, and the intensity of the experimental Pt atomic XAFS correlates with the Lewis acidity of the cation introduced. Furthermore, it was found that the CO coverage increases with increasing electron density on the Pt nanoparticles. This increasing electron density was found to result in an increased CO oxidation activity; i.e., the T 50% for CO oxidation decreases with decreasing R. In other words, basic promotors facilitate the chemisorption of CO on the Pt particles. The most promoted CO oxidation catalyst is a Pt/K-Y sample, which has a T 50% of 390 K and a L:B intensity ratio of 2.7. The obtained results provide guidelines to design improved CO oxidation catalysts.

Multiple in situ and time-resolved spectroscopic techniques (EDXAFS, UV-vis, EPR, and NMR), with a focus on simultaneously acquired EDXAFS and time-resolved UV-vis, are described to reveal detailed structural and electronic information on reaction intermediates of an important Cu(II)-catalyzed N-arylation of imidazole. The N-arylation of imidazole was performed in a NMP/ H 2 O solvent mixture, at ambient temperature and atmosphere, using the commercially available Cu catalyst [Cu(OH)(TMEDA)] 2 Cl 2 (I). The spectroscopic study resulted in the characterization of most reaction intermediates, and a novel mechanism for the Cu(II)-catalyzed arylation reaction is proposed. The first and selectivity-determining step is the reaction of the dimeric Cu(II) starting complex with imidazole, forming a mononuclear Cu(II)(imidazole) intermediate, II. After subsequent addition of phenylboronic acid, we propose the formation of a Cu(III)(imidazolate)(phenyl) intermediate, III, which after reductive elimination forms the phenylimidazole product, and a known Cu(I) monomeric species, IV, is identified. Finally, this Cu species is reoxidized, forming back an equilibrium mixture of Cu(II) mononuclear and dinuclear complexes. Inhibition of the reaction by imidazole and phenylimidazole is observed. The phenylboronic acid is, in combination with H 2 O, involved in the oxidation and reoxidation steps in the described catalytic cycle.