A new set-up is reported of an indirect cryogenic cooling system for a double-crystal monochromator which runs on the BM30b/FAME beamline at the ESRF (Grenoble, France). This device has been conceived to limit the vibrations on the first diffracting crystal and to maintain it at a constant temperature. These points are crucial for maximizing the beamline stability. Moreover, the relative angular position of the second crystal can be dynamically adjusted by a piezoelectric transducer coupled with a feedback system in order to always be at the maximum of the rocking curve during an X-ray absorption spectroscopy scan. The temperature is stabilized to an accuracy of 0.01 degrees , with two principal consequences. The energy resolution is close to the theoretical value [DeltaE/E = 5.6 x 10(-6) for Si(220)] and the precision of the energy positioning is extremely good even if the power load changes. A feedback mechanism allows a permanent and automatic optimization of the angle between the two crystals of the monochromator. The intensity of the monochromatic beam remains optimized (i) when the intensity of the electron beam decreases in the storage ring and (ii) during an energy scan.

Methanol synthesis by means of direct CO 2 hydrogenation has the potential to contribute to climate change mitigation by turning the most important greenhouse gas into a commodity. However, for this process to become industrially relevant, catalytic systems with improved activity, selectivity and stability are required. Here we explore the potential of metal-organic frameworks (MOF) as precursors for synthesis of Co 3 O 4 -supported In 2 O 3 oxide composites for the direct CO 2 hydrogenation to methanol. Stepwise pyrolytic-oxidative decomposition of indium-impregnated ZIF-67(Co) MOF affords the formation of a nanostructured In 2 O 3 @Co 3 O 4 reticulated shell composite material able to reach a maximum methanol production rate of 0.65 g MeOH •g cat -1 •h -1 with selectivity as high as 87% over 100 h on stream. Textural characteristics of the sacrificial ZIF-67(Co) matrix and In-loading were found to be important variables for optimizing the catalyst performance such as induction time, methanol productivity and selectivity. The structural investigation on the catalytic system reveals that the catalyst undergoes reorganization under reaction conditions, transforming from a Co 3 O 4 with amorphous In 2 O 3 shell into Co 3 InC 0.75 covered by a layer consisting of a mixture of amorphous CoO x and In 2 O 3 oxides. Structural reorganization is responsible for the observed induction period, while the amorphous mixed cobalt indium oxide shell is responsible for the high methanol yield and selectivity. Additionally, these results demonstrate the tunable performance of MOF-derived In 2 O 3 @Co 3 O 4 catalyst as a function of the reaction conditions which allows to establish a reasonable trade-off between high methanol yield and selectivity in a wide temperature and pressure window.

The local hydrogen-bonding environment in supercritical water (380 degrees C, 300 bars, density 0.54 gcm3) was studied by x-ray Raman scattering at the oxygen K edge. The spectra are compared to those of the gas phase, liquid surface, bulk liquid, and bulk ice, as well as to calculated spectra. The experimental model systems are used to assign spectral features and to quantify specific local hydrogen-bonding situations in supercritical water. The first coordination shell of the molecules is characterized in more detail with the aid of the calculations. Our analysis suggests that approximately 65% of the molecules in supercritical water are hydrogen bonded in configurations that are distinctly different from those in liquid water and ice. In contrast to liquid water the bonded molecules in supercritical water have four intact hydrogen bonds and in contrast to ice large variations of bond angles and distances are observed. The remaining approximately 35% of the molecules exhibit two free O-H bonds and are thus either not involved in hydrogen bonding at all or have one or two hydrogen bonds on the oxygen side. We determine an average O-O distance of 3.1+/-0.1 A in supercritical water for the H bonded molecules at the conditions studied here. This and the corresponding hydrogen bond lengths are shown to agree with neutron- and x-ray-diffraction data at similar conditions. Our results on the local hydrogen-bonding environment with mainly two disparate hydrogen-bonding configurations are consistent with an extended structural model of supercritical water as a heterogeneous system with small patches of bonded molecules in various tetrahedral configurations and surrounding nonbonded gas-phase-like molecules.