Hard x-ray photon-in-photon-out spectroscopy with lifetime resolution – of XAS, XES, RIXSS and HERFD

Spectroscopic techniques that aim to resolve the electronic configuration and local coordination of a central atom by detecting inner-shell radiative decays following photoexcitation using hard X-rays are presented. The experimental setup requires an X-ray spectrometer based on perfect crystal Bragg optics. The possibilities arising from non-resonant (X-Ray Emission Spectroscopy - XES) and resonant excitation (Resonant Inelastic X-Ray Scattering Spectroscopy – RIXSS, High-Energy-Resolution Fluorescence Detected (HERFD) XAS) are discussed when the instrumental energy broadenings of the primary (beamline) monochromator and the crystal spectrometer for x-ray emission detection are on the order of the core hole lifetimes of the intermediate and final electronic states. The small energy bandwidth in the emission detection yields line-sharpened absorption features. In transition metal compounds, electron-electron interactions as well as orbital splittings and fractional population can be revealed. Combination with EXAFS spectroscopy enables to extent the k-range beyond unwanted absorption edges in the sample that limit the EXAFS range in conventional absorption spectroscopy

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO₂ storage site before CO₂ arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2

Post-Combustion CO

Simulation results in the literature suggest that Vacuum Swing Adsorption (VSA) processes using physisorbents might largely outperform the current state-of-the-art post-combustion CO2 capture technologies based on amine solvents in terms of energy consumption. Most studies consider the zeolite NaX as adsorbent. NaX has a very strong affinity for CO2 but is difficult to regenerate and very sensitive to the presence of water in the flue gas. By tuning the polarity of the adsorbent, it might be possible to find a better compromise between adsorption capacity, regenerability and sensitivity to H2O. In the present contribution, we therefore screen the performance of a series of zeolites as physisorbents in a VSA process for CO2 capture. The adsorbents are tested by breakthrough experiments of a dry and wet model flue gas, in once-through and cyclic operation. The most interesting material, zeolite EMC-1, is selected for numerical simulations of a full VSA cycle, in comparison with zeolite NaX. Both solids satisfy the performance targets in terms of recovery (> 90%) and purity of CO2 (> 95%) but the very low pressure required for regeneration of the adsorbents will be a serious handicap for the deployment of this technology on a large scale

Metal Organic Framework Materials for Desulfurization by Adsorption

Current European regulations limit the sulfur content of gasoline to 10 ppmw. Such deep desulfurization levels can be achieved by catalytic hydrodesulfurization processes, but they are accompanied by excessive H2 consumption for unwanted side reactions, in particular, for the hydrogenation of olefins. Selective adsorption constitutes an attractive alternative to catalytic desulfurization. The main challenge is to find adsorbents able to remove the sulfur compounds with very high selectivity from a complex mixture of paraffins, naphthenes, olefins, and aromatic compounds. In the present contribution we present the screening of a large number of metal?organic frameworks (MOFs) for this purpose, using batch adsorption experiments. For the two most promising structures (HKUST-1 and CPO-27-Ni, two cus-MOFs, that is, with coordinatively unsaturated sites), the dynamic behavior, the impact of a model nitrogen-containing compound (pyridine) on the adsorption properties, as well as the regenerability were also evaluated by breakthrough experiments. The good results obtained in purification of our model feeds incited us to perform measurements with a real gasoline feed using batch measurements. The feasibility of adsorptive desulfurization of gasoline using MOFs is discussed on the basis of these results

the effects of support acidity on quinoline and indole hydrodenitrogenation - a detailed kinetic study

SSCI-VIDE+ECI2D+MNG:CGEInternational audienceA detailed kinetic modeling including the liquid-vapor mass transfer was proposed to estimate kinetic and adsorption constants in complex reaction scheme and discriminate the support acidity effects on quinoline and indole HDN. The catalytic tests were carried out in a batch reactor, over two sulfide catalysts: NiMo(P)/γ-Al2O3 and NiMo(P)/SiO2-Al2O3 (ASA). Over both catalysts, the hydrogenation of aromatic ring of nitrogen compounds is the rate determining step of the main reaction pathway. The NiMo(P)/ASA exhibited higher rate constants for this step and denitrogenation steps (without ring opening). The adsorption constants of all nitrogen compounds were compared. As expected, nitrogen compounds adsorbed more strongly on NiMo(P)/ASA than Al2O3 counterpart. Quinoline showed a strong inhibiting effect on indole HDN whereas the inhibiting effect of indole on quinoline HDN was negligible over NiMo(P)/Al2O3 and slightly more important over NiMo(P)/ASA

Use of kinetic modeling for investigating support acidity effects of NiMo sulfide catalysts on quinoline hydrodenitrogenation

SSCI-VIDE+ECI2D+MNG:MTF:CGEInternational audienceA detailed kinetic study of the hydrodenitrogenation (HDN) network of quinoline was carried out over Ni-promoted MoS2 catalysts supported either on gamma-Al2O3 or on amorphous silica alumina (ASA), the objective is to identify the role of the support acidity in HDN reactions. The kinetic data obtained from catalytic tests in a batch reactor were analyzed by a model including the liquid-vapor mass transfer. The adsorption constants of all intermediates and the kinetic constants of all elementary steps were estimated. We found that the NiMo(P)/ASA exhibited a higher rate constant in the hydrogenation of tetrahydroquinoline, which was the rate determining step of the main reaction pathway, and in exocyclic carbon-nitrogen bond cleavage reactions, than the NiMo(P)/Al2O3. Characterization data by Infra-Red spectroscopy of CO suggested that this result might be related to the modification of the electronic properties of promoted NiMoS phase due to higher acidity of ASA. However, the stronger self-inhibiting effect due to stronger adsorption of nitrogen compounds over NiMo(P)/ASA and its lower content of NiMoS phase decreased its global catalytic activity. (C) 2016 Elsevier B.V. All rights reserved

Post-Combustion CO 2

Simulation results in the literature suggest that Vacuum Swing Adsorption (VSA) processes using physisorbents might largely outperform the current state-of-the-art post-combustion CO2 capture technologies based on amine solvents in terms of energy consumption. Most studies consider the zeolite NaX as adsorbent. NaX has a very strong affinity for CO2 but is difficult to regenerate and very sensitive to the presence of water in the flue gas. By tuning the polarity of the adsorbent, it might be possible to find a better compromise between adsorption capacity, regenerability and sensitivity to H2O. In the present contribution, we therefore screen the performance of a series of zeolites as physisorbents in a VSA process for CO2 capture. The adsorbents are tested by breakthrough experiments of a dry and wet model flue gas, in once-through and cyclic operation. The most interesting material, zeolite EMC-1, is selected for numerical simulations of a full VSA cycle, in comparison with zeolite NaX. Both solids satisfy the performance targets in terms of recovery (> 90%) and purity of CO2 (> 95%) but the very low pressure required for regeneration of the adsorbents will be a serious handicap for the deployment of this technology on a large scale