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Iron is considered as attractive energy carrier in a carbon‐free, circular energy economy. The reduction of iron oxide is crucial for its application as a metal fuel as it determines the efficiency of the cycle. Temperature programmed reduction of α‐Fe2O3 was monitored by complementary X‐ray absorption spectroscopy (XAS) and diffraction (XRD) to obtain the phase composition with high time resolution. Synchrotron Mössbauer spectroscopy (SMS) was additionally employed due to its high sensitivity to the different iron species. Theoretical calculations of surface and bulk adsorption processes were performed to establish the potential reaction pathways and the corresponding energy barriers. A kinetic particle model was then developed to bridge the experimental data and theoretical calculations, which reproduced the reduction onset and behavior. The reduction process was found to be strongly dependent on the heating rate in terms of the reduction window and the observed intermediate species. We propose that a core‐shell mechanism determines the reaction by forming an iron layer which subsequently hinders diffusion of water out of the porous particles leading to some unreduced FeO at high temperature. This study demonstrates the need for complementary methods for describing complex heterogeneous systems and overcoming the chemical sensitivity limitations of any single method. [ABSTRACT FROM AUTHOR]

Ethylene dimerization is an industrial process that is currently carried out using homogeneous catalysts. Here we present a highly active heterogeneous catalyst containing minute amounts of atomically dispersed Pd. It requires no co‐catalyst(s) or activator(s) and significantly outperforms previously reported catalysts tested under similar reaction conditions. The selectivity to C4‐ and C6‐hydrocarbons was about 80 % and 10 % at 42 % ethylene conversion at 200 °C using an industrially relevant feed containing 50 vol % ethylene, respectively. Our kinetic and catalyst characterization experiments complemented by density functional theory calculations provide molecular insights into the local environment of isolated Pd(II)Ox species and their role in achieving high activity in the target reaction. When the developed catalyst was rationally integrated with a Mo‐containing olefin metathesis catalyst in the same reactor, the formed butenes reacted with ethylene to propylene with a selectivity of 98 % at about 24 % ethylene conversion. [ABSTRACT FROM AUTHOR]

Die Ethylen‐Dimerisierung ist ein industrieller Prozess, der derzeit mit homogenen Katalysatoren durchgeführt wird. Hier stellen wir einen hochaktiven heterogenen Katalysator vor, der winzige Mengen von atomar dispergiertem Pd enthält. Er erfordert keine Cokatalysatoren oder Aktivatoren und übertrifft die Leistung früherer Katalysatoren, die unter ähnlichen Reaktionsbedingungen getestet wurden. Die Selektivität für C4‐ und C6‐Kohlenwasserstoffe betrug bei 200 °C etwa 80 % bzw. 10 % bei 42 % C2H4‐Umsatz unter Verwendung eines industriell relevanten Reaktionsgemisches mit 50 Vol.‐% Ethylen. Unsere Experimente zur Kinetik und Katalysatorcharakterisierung, ergänzt durch Dichtefunktionaltheorie‐Berechnungen, liefern molekulare Einblicke in die lokale Umgebung isolierter Pd(II)Ox‐Spezies und ihre Rolle bei der Erzielung einer hohen Aktivität in der Zielreaktion. Als der entwickelte Katalysator rationell mit einem Mo‐haltigen Olefinmetathesekatalysator im gleichen Reaktor integriert wurde, reagierten die gebildeten Butene mit Ethylen zu Propylen mit einer Selektivität von 98 % bei etwa 24 % C2H4‐Umsatz. [ABSTRACT FROM AUTHOR]

Here, we present new cryogenic infrared spectra of the (Imidazole) n H + (n=1,2,3) ions. The data was obtained using helium tagging infrared predissociation spectroscopy. The new results were compared with the data obtained by Gerardi et al. (Chem. Phys. Lett. 501:172–178, 2011) using the same technique but with argon as a tag. Comparison of the two experiments, assisted by theoretical calculations, allowed us to evaluate the preferable attachment positions of argon to the (Imidazole) n H + frame. Argon attaches to nitrogen-bonded hydrogen in the case of the (Imidazole)H + ion, while in (Imidazole) 2 H + and (Imidazole) 3 H + the preferred docking sites for the argon are in the center of the complex. This conclusion is supported by analyzing the spectral features attributed to the N–H stretching vibrations. Symmetry adapted perturbation theory (SAPT) analysis of the non-covalent forces between argon and the (Imidazole) n H + (n=1,2,3) frame revealed that this switch of docking preference with increasing complex size is caused by an interplay between induction and dispersion interactions. [ABSTRACT FROM AUTHOR]

The discovery and development of new synthetic methods exploiting earth-abundant-element-based catalysts is an important goal in contemporary synthetic organic chemistry, which faces increasingly stringent requirements of sustainability. In this work, we disclose alumina-mediated propargylic C–H activation inducing a challenging transformation of readily available alkynes into a valuable 1,3-diene moiety under unprecedentedly mild conditions. Combining DFT-investigation and synthetic observations, we demonstrate that partial hydroxylation of alumina's surface might play an essential role in this process. [ABSTRACT FROM AUTHOR]

The synthesis of an unprecedented, π‐extended hexabenzocorene (HBC)‐based diaza[7]helicene is presented. The target compound was synthesized by an ortho‐fusion of two naphthalene diimide (NDI) units to a HBC‐skeleton. A combination of Diels–Alder and Scholl‐type oxidation reactions involving a symmetric di‐NDI‐tolane precursor were crucial for the very selective formation of the helical superstructure via a hexaphenyl‐benzene (HPB) derivative. The formation of the diaza[7]helicene moiety in the final Scholl oxidation is favoured, affording the symmetric π‐extended helicene as the major product as a pair of enantiomers. The separation of the enantiomers was successfully accomplished by HPLC involving a chiral stationary phase. The absolute configuration of the enantiomers was assigned by comparison of circular dichroism spectra with quantum mechanical calculations. [ABSTRACT FROM AUTHOR]