Ad M. J. van der Eerden

Implementation of a combined SAXS/WAXS/QEXAFS set-up for time-resolved in situ experiments

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.

Deactivation processes of homogeneous Pd catalysts using in situ time resolved spectroscopic techniquesElectronic supplementary information (ESI) available: EXAFS data and Fourier Transform. See http://www.rsc.org/suppdata/cc/b2/b206758g/

UV-Vis, combined with ED-XAFS shows, for the first time, the evolution of inactive Pd dimers and trimers, that are a possible first stage in the deactivation process of important palladium catalysed reactions, leading to larger palladium clusters and eventually palladium black.

Nitrogen storage in biotite: An experimental study of the ammonium and potassium partitioning between 1M-phlogopite and vapour at 2 kb

Abstract The NH+4 and K+ distribution between phlogopite and a chloride vapour phase was investigated at 550°C and 2000 bars. Some preliminary data are reported for 650°C and 2000 bars. The apparent distribution coefficient, K ∗ D = (NH + 4 K + ) phlogopite p,t (NH + 4 K + ) vapour 1 bar, 25°C , is 1.29 ± 0.30 at 550°C and 1.44 ± 0.20 for the preliminary data at 650°C. At 550°C a series of runs was performed to study the equilibration time of the exchange reaction. Bulk compositions requiring a large change in solid composition did not equilibrate within 28 days, indicating a rather sluggish reaction mechanism. The extrapolation to low NH+4 concentrations in natural rock systems may provide estimates of NH+4 concentrations for metamorphic fluids in equilibrium with NH+4 bearing minerals. The assumption that Rb+ behaves similarly to NH+4 allows a rough estimate of the distribution coefficients for NH+4 in other minerals. Semiquantitative modelling based on the derived distribution coefficients of NH+4 and Rb+ may elucidate fluid rock equilibria during closed system behaviour. The release of nitrogen by breakdown of NH4-bearing biotite during prograde or retrograde processes in metamorphic rocks may explain the presence of N2-gas in fluid inclusions.

Adding a third dimension to operando spectroscopy: a combined UV-Vis, Raman and XAFS setup to study heterogeneous catalysts under working conditions

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.

Promotion effects in the oxidation of CO over zeolite-supported Rh nanoparticles

Rh particles with an average diameter smaller than 1.5 nm have been supported on a series of zeolite Y samples. These zeolite materials contained different monovalent (H+, Na+, K+, Rb+, and Cs+) and divalent (Mg2+, Ca2+, Sr2+, and Ba2+) cations and were used as model systems to investigate the effect of promoter elements in the oxidation of CO over supported Rh particles in excess of oxygen. Infrared (IR) spectroscopy was carried out to monitor the electronic changes in the local environment of Rh-adsorbed CO. It was found that the bands corresponding to two Rh gem-dicarbonyl species, Rh+(CO)2-(Oz)2 and Rh+(CO)2-(Oz)(H2O), shift to lower wavenumbers with increasing ionic radius/charge ratio of the cation. In addition, the relative intensity of the bridge bonded CO as compared to the total absorbance of Rh-bonded CO species decreases with increasing Lewis acidity, as expressed by the Kamlet-Taft parameter R of the cation. This trend could be directly correlated to the Rh CO oxidation activity, since low temperatures at 50% CO conversion corresponded with catalyst materials with a high contribution of bridge-bonded CO species and hence with small R values. A lower Lewis acidity causes an increased electron density on the framework oxygen atoms and thus an increased electron density on the zeolite-supported Rh particles. Comparable trends have been observed previously on a similar series of cation containing zeolite supported Pt catalyst materials.

Structural properties of subnanometer thick Y layers in extreme ultraviolet multilayer mirrors.

We studied the structure and optical properties of B(4)C/Mo/Y/Si multilayer systems. Using extended x-ray absorption fine structure measurements at the Y and Mo K-edge, the structure of the subnanometer thick Y layer and the underlying Mo layer were analyzed. It was found that even a 0.2 nm thick Y layer significantly reduced silicon diffusion toward Mo, thus reducing Mo silicide formation. Hard x-ray reflectometry showed that the difference in average interface roughness of the B(4)C/Mo/Y/Si multilayer structure compared to Mo/Si and B(4)C/Mo/B(4)C/Si multilayer structures was negligible. Soft x-ray reflectometry showed optical improvement of B(4)C/Mo/Y/Si with respect to Mo/Si and B(4)C/Mo/B(4)C/Si multilayer structures.

Superior Stability of Au/SiO2 Compared to Au/TiO2 Catalysts for the Selective Hydrogenation of Butadiene

Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2–4 nm Au nanoparticulate catalysts, supported on either TiO2 or SiO2, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports. At full conversion of butadiene, only 0.1% of the propene was converted for both supported catalysts, demonstrating their high selectivity. The TiO2-supported catalysts showed a steady loss of activity, which was recovered by heating in air. We demonstrated that the deactivation was not caused by significant metal particle growth or strong metal–support interaction, but rather, it is related to the deposition of carbonaceous species under reaction conditions. In contrast, all the SiO2-supported catalysts were highly stable, with very limited formation of carbonaceous deposits. It shows that SiO2-supported catalysts, despite their 2–3 times lower initial activities, clearly outperform TiO2-supported catalysts within a day of run time.

Combined time-resolved SAXS and X-ray Spectroscopy methods

Recently developed equipment suitable for quasi simultaneous data collection of SAXS/WAXS and X-ray spectroscopy is discussed. The main applications for this technique are foreseen to be time-resolved studies in inorganic materials relevant for catalysis research and ceramics. The equipment is described and experimental limitations are discussed. Experiments on nanoparticle synthesis and the formation of inorganic materials for catalysis are used as examples of the usefulness of the developed equipment.