The manufacturing steps and first tests of a refractive lens made of polycrystalline diamond are described. A fabrication process based on electron-beam lithography and deep reactive ion etching is introduced. Experimental tests on beamline ID13 at the ESRF have been performed. A spot size of 360nm (FWHM) at an energy E = 24.3keV is observed.

We describe the hard X-ray scanning microscope planned for the new synchrotron radiation source PETRA III at DESY in Hamburg, Germany. It is based on nanofocusing refractive X-ray lenses and is designed for two-dimensional mapping and scanning tomography. It supports X-ray fluorescence and (coherent) diffraction contrast, yielding elemental and structural information from inside the sample. Spatial resolutions down to well below 50 nm are aimed for in direct space. A further increase in spatial resolution is expected by applying ptychographic scanning schemes. The optical scheme with a two-stage focusing optic is described.

Spectroscopic studies on heterogeneous catalysts have mostly been done in an integral mode. However, in many cases spatial variations in catalyst structure can occur, e.g. during impregnation of pre-shaped particles, during reaction in a catalytic reactor, or in microstructured reactors as the present overview shows. Therefore, spatially resolved molecular information on a microscale is required for a comprehensive understanding of theses systems, partly in ex situ studies, partly under stationary reaction conditions and in some cases even under dynamic reaction conditions.Among the different available techniques, X-ray absorption spectroscopy (XAS) is a well-suited tool for this purpose as the different selected examples highlight. Two different techniques, scanning and full-field X-ray microscopy/tomography, are described and compared. At first, the tomographic structure of impregnated alumina pellets is presented using full-field transmission microtomography and compared to the results obtained with a scanning X-ray microbeam technique to analyse the catalyst bed inside a catalytic quartz glass reactor. On the other hand, by using XAS in scanning microtomography, the structure and the distribution of Cu(0), Cu(I), Cu(II) species in a Cu/ZnO catalyst loaded in a quartz capillary microreactor could be reconstructed quantitatively on a virtual section through the reactor. An illustrating example for spatially resolved XAS under reaction conditions is the partial oxidation of methane over noble metal-based catalysts. In order to obtain spectroscopic information on the spatial variation of the oxidation state of the catalyst inside the reactor XAS spectra were recorded by scanning with a micro-focussed beam along the catalyst bed. Alternatively, full-field transmission imaging was used to efficiently determine the distribution of the oxidation state of a catalyst inside a reactor under reaction conditions. The new technical approaches together with quantitative data analysis and an appropriate in situ catalytic experiment allowed drawing important conclusions on the reaction mechanism, and the analytical strategy might be similarly applied in other case studies. The corresponding temperature profiles and the catalytic performance were measured by means of an IR-camera and mass spectrometric analysis. In a more advanced experiment the ignition process of the partial oxidation of methane was followed in a spatiotemporal manner which demonstrates that spatially resolved spectroscopic information can even be obtained in the subsecond scale. (C) 2008 Elsevier B.V. All rights reserved.

The catalytic partial oxidation of methane (CPO) over flame-made 2.5%Rh–2.5%Pt/Al2O3 and 2.5%Rh/Al2O3 in 6%CH4/3%O2/He shows the potential of in situ studies using miniaturized fixed-bed reactors, the importance of spatially resolved studies and its combination with infrared thermography and on-line mass spectrometry. This experimental strategy allowed collecting data on the structure of the noble metal (oxidation state) and the temperature along the catalyst bed. The reaction was investigated in a fixed-bed quartz microreactor (1–1.5 mm diameter) following the catalytic performance by on-line gas mass spectrometry (MS). Above the ignition temperature of the catalytic partial oxidation of methane (310–330 °C), a zone with oxidized noble metals was observed in the inlet region of the catalyst bed, accompanied by a characteristic hot spot (over-temperature up to 150 °C), while reduced noble metal species became dominant towards the outlet of the bed. The position of both the gradient in oxidation state and the hot spot were strongly dependent on the furnace temperature and the gas flow (residence time). Heating as well as a higher flow rate caused a migration of the transition zone of the oxidation state/maximum in temperature towards the inlet. At the same time the hydrogen concentration in the reactor effluent increased. In contrast, at low temperatures a movement of the transition zone towards the outlet was observed at increasing flux, except if the self-heating by the exothermic methane oxidation was too strong. The results indicate that in the oxidized zone mainly combustion of methane occurs, whereas in the reduced part direct partial oxidation and reforming reactions prevail. The results demonstrate how spatially resolved spectroscopy can help in understanding catalytic reactions involving different reaction zones and gradients even in micro scale fixed-bed reactors.

Based on nanofocusing parabolic refractive x-ray lenses we have developed and built a hard x-ray scanning microscope that was tested and put to use at beamline ID13 of the ESRF. It can provide a monochromatic hard x-ray nanobeam with lateral extension below 100 nm (down to 50 nm) and a flux up to 10(9) ph/s in the energy range from 15 to 25 keV. The microscope exploits transmission, fluorescence, and diffraction contrast to obtain local elemental and nanostructural information from the sample. Tomographic scanning yields high resolution elemental maps from the inside of an object. Coherent x-ray diffraction imaging with nanofocused illumination yields images of objects with highest spatial resolution, e. g., 5 nm in a given example.

We present a spatiotemporal operando X-ray absorption study of a highly dynamic process, the ignition of the noble metal catalyzed partial oxidation of methane. Evolvement and propagation of the platinum component's structural changes are investigated with a high-speed X-ray camera, which in combination with temperature profiling by IR-thermography and catalytic activity measurements by online mass spectrometry gives insight into the first stages of the ignition of the reaction toward hydrogen and carbon monoxide.

Nanofocusing refractive x-ray lenses (NFLs) form the basis of a hard x-ray scanning microscope. They are characterized by their short focal length (~ 10 mm at 15 keV to 25 keV) and large numerical aperture, allowing for the generation of hard x-ray nanobeams even at short distances from a synchrotron radiation source. These optics, made out of silicon by electron beam lithography and subsequent deep reactive ion etching, have been shown to focus hard x-rays down to 50 nm. We have modeled these optics, allowing us to characterize slight aberrations and the wave-field properties in the focus by analyzing the beam profile in the far field.

A parallel reactor cell for catalytic in situ X-ray absorption spectroscopy (XAS) measurements was developed. The cell facilitates the Simultaneous catalytic and structural investigation of six catalysts under different feed gas conditions. A two-dimensional X-ray sensor was used for spectra collection. Gas compositions were measured by on-line mass spectrometry. The potential and limitations of the high throughput XAS cell are discussed. The heterogeneously catalyzed partial oxidation of methane (CPO) was chosen as a test reaction. Alumina-supported Rh and Au/Rh catalysts with different metal loadings (0.5-2.5 wt%) were applied and prepared via different preparation routes using flame spray pyrolysis (fsp) and colloid adsorption (col). For comparison the same catalysts were also investigated in a fixed-bed capillary reactor heated by a gas blower (also for XAS measurements) and in an eight-fold parallel gas phase reactor using similar reaction conditions (6% CH4-3% O-2-He, 250-500 degrees C). Similar catalytic results were obtained in all three reactor types, confirming the suitability of the parallel reactor XAS cell for catalytic measurements. The catalysts showed different activity, selectivity and reducibility depending on metal loading, preparation route and Au/Rh ratio. The analysis of the catalytic data, STEM images and the in situ XANES experiments of the various catalysts indicated the following characteristics for the CPO reaction: sufficient heat production by combustion of methane, total conversion of oxygen, and reduction of a certain fraction of the catalyst. The overall catalytic behavior was in line with a two-zone model of the catalyst bed where catalytic combustion dominates in the front zone and reforming reactions become favored in the second part of the catalyst bed. (C) 2008 Elsevier B.V. All rights reserved.

X-Ray absorption spectroscopy using a microreactor array in combination with an X-ray camera is applied for fast parallel structural screening of a variety of differently prepared supported palladium and copper particles in the as-prepared state and after heat pre-treatments in different gas atmospheres.

During the catalytic partial oxidation (CPO) of methane to hydrogen and carbon monoxide distinct spatial changes of the catalyst structure in a microreactor containing a fixed-bed of 2.5 wt% Rh/Al2O3 were observed depending on temperature and space velocity. The variation of the catalyst structure along the catalyst bed was determined by X-ray absorption spectroscopy. In a first step the catalyst bed was scanned with a small X-ray beam. Then, more detailed information on the oxidation state of Rh along the catalyst bed was extracted by recording absorption images using a position sensitive X-ray camera. The studies were combined with on-line mass spectrometry providing information on the catalytic performance of the catalyst simultaneously.Mainly oxidized Rh-particles were found below the ignition temperature (310 degrees C) of the partial oxidation of methane to hydrogen and carbon monoxide. Hardly any structural changes were observed when oxidation to water and carbon dioxide occurred, but strong variations over the catalyst bed were detected when the CPO-reaction started. In the entrance zone of the catalyst bed the rhodium species were mainly in oxidized state, whereas they were in metallic state towards the end of the catalyst bed. Usually, a steep gradient within less than 100 mu m was observed. Furthermore, at higher temperature, a characteristic cone towards the inlet of the spectroscopic cell was observed. Upon temperature increase the gradient zone moved towards the inlet. The variation of the space velocity also resulted in a shift as well as a change in the shape of the profile. (c) 2006 Elsevier B.V All rights reserved.

Structure-performance relationships gained by studying catalysts at work are considered the key to further development of catalysts. This requires the structural identification of catalysts preferentially under process conditions while measuring the catalytic activity at the same time. In situ X-ray absorption spectroscopy is a well-suited technique for this purpose since it can identify the chemical states of both crystalline and amorphous structures. Up to now studies were performed in an 'integral' way, i.e. averaged over the whole reactor. Here, we studied the partial oxidation of methane over a 2.5wt% Rh/A1203 catalyst, which is a promising reaction for the production of hydrogen from natural gas. The experimental arrangement and a transmission X-ray image of the catalyst bed are shown in Fig. 1. When the catalyst was heated up in a CHi02 mixture (ratio 2:1), the reaction to hydrogen and CO ignited at about 320°C, and at the same time the Rh particles were reduced. However, a closer look revealed that the Rh particles at the inlet of the catalyst bed (ca. 12 mm in length) were oxidized whereas towards the outlet they were in metallic state. This can be extracted from the characteristic spectra for oxidized and reduced Rh (Fig. 1). In a next step we aimed at 2-D mapping of the oxidation state of Rh on a micrometer scale. An Xray camera was installed behind the reactor to record the transmitted intensity with and without the reactor as function of the energy. In this way 160 X-ray absorption images were taken around the Rh Kedge, four of them being shown in Fig. 2 (top). These X-ray absorption images contain the full absorption spectroscopic information in the XANES region at each point of the reactor. Therefore reconstruction of the spectra and a linear combination fit with spectra for Rho, Rh3+ and an uncharacteristic background allows extracting the 2-D distribution of these components (Fig. 2, bottom). Alternatively, also microXAS studies using a beam of a few micrometers in size would provide similar insight into the reactor. A parallelization using dispersive EXAFS or the use of a quick scanning monochromator would, however, be needed for the latter approach. Parallelization in the present study was achieved using the X-ray camera. The results demonstrate that the structure of a catalyst may vary inside a catalytic reactor. For the first time 2-D mapping of a catalyst bed under catalytic reaction conditions was achieved.