Operando Photo-Electrochemical Catalysts Synchrotron Studies

The attempts to develop efficient methods of solar energy conversion into chemical fuel are ongoing amid climate changes associated with global warming. Photo-electrocatalytic (PEC) water splitting and CO2 reduction reactions show high potential to tackle this challenge. However, the development of economically feasible solutions of PEC solar energy conversion requires novel efficient and stable earth-abundant nanostructured materials. The latter are hardly available without detailed understanding of the local atomic and electronic structure dynamics and mechanisms of the processes occurring during chemical reactions on the catalyst–electrolyte interface. This review considers recent efforts to study photo-electrocatalytic reactions using in situ and operando synchrotron spectroscopies. Particular attention is paid to the operando reaction mechanisms, which were established using X-ray Absorption (XAS) and X-ray Photoelectron (XPS) Spectroscopies. Operando cells that are needed to perform such experiments on synchrotron are covered. Classical and modern theoretical approaches to extract structural information from X-ray Absorption Near-Edge Structure (XANES) spectra are discussed

Experimental and theoretical study of hydrogen desorption process from Mn(BH4)2

The thermal decomposition of manganese borohydride Mn(BH4)2 was studied by means of synchrotron-based X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XRPD) and theoretical density functional (DFT) modeling aiming to elucidate changes of the local atomic structure upon hydrogen desorption and to determine possible decomposition reaction products. XRPD patterns indicate profound structural changes in the material above 120 °C with subsequent amorphization. DFT simulations predict the collapse of the highly porous framework structure upon hydrogen desorption and significant reduction of Mn-B and Mn-Mn interatomic distances by 19% and 41% respectively. These estimations are in a good agreement with the quantitative analysis of the X-ray absorption spectra above Mn K-edge. Based on XAS we derive possible decomposition products and reaction path. In particular, the amount of Mn metallic phase was estimated to be less than 5% after the heating up to 200 °C. Several structural models for the final state of manganese borohydride in a heating process are constructed by means of energy minimization in conjunction with evolutionary algorithms

STUDY ON THE SYSTEMATIC DESIGN OF TURBO-PUMPS AND THEIR PERFORMANCE CHARACTERISTICS (1st Report) : The systematic design procedure of four mixed-flow pumps

Cu-exchanged zeolites possess active sites that are able to cleave the C–H bond of methane at temperatures ≤200 °C, enabling its selective partial oxidation to methanol. Herein we explore this process over Cu-SSZ-13 materials. We combine activity tests and X-ray absorption spectroscopy (XAS) to thoroughly investigate the influence of reaction parameters and material elemental composition on the productivity and Cu speciation during the key process steps. We find that the CuII moieties responsible for the conversion are formed in the presence of O2 and that high temperature together with prolonged activation time increases the population of such active sites. We evidence a linear correlation between the reducibility of the materials and their methanol productivity. By optimizing the process conditions and material composition, we are able to reach a methanol productivity as high as 0.2 mol CH3OH/mol Cu (125 μmol/g), the highest value reported to date for Cu-SSZ-13. Our results clearly demonstrate that high populations of 2Al Z2CuII sites in 6r, favored at low values of both Si:Al and Cu:Al ratios, inhibit the material performance by being inactive for the conversion. Z[CuIIOH] complexes, although shown to be inactive, are identified as the precursors to the methane-converting active sites. By critical examination of the reported catalytic and spectroscopic evidence, we propose different possible routes for active-site formation