Towards Green Ammonia Synthesis through Plasma-Driven Nitrogen Oxidation and Catalytic Reduction

Ammonia is an industrial large-volume chemical, with its main application in fertilizer production. It also attracts increasing attention as a green-energy vector. Over the past century, ammonia production has been dominated by the Haber–Bosch process, in which a mixture of nitrogen and hydrogen gas is converted to ammonia at high temperatures and pressures. Haber–Bosch processes with natural gas as the source of hydrogen are responsible for a significant share of the global CO₂ emissions. Processes involving plasma are currently being investigated as an alternative for decentralized ammonia production powered by renewable energy sources. In this work, we present the PNOCRA process (plasma nitrogen oxidation and catalytic reduction to ammonia), combining plasma-assisted nitrogen oxidation and lean NO_x trap technology, adopted from diesel-engine exhaust gas aftertreatment technology. PNOCRA achieves an energy requirement of 4.6 MJ mol⁻¹ NH₃, which is more than four times less than the state-of-the-art plasma-enabled ammonia synthesis from N₂ and H₂ with reasonable yield (>1 %).     

Effect of Inorganic Phosphate on the Photoproduction of Hydrogen Peroxide in Frozen Aqueous Solutions of Adenine Derivatives

Russian Journal of Physical Chemistry A - The content of hydrogen peroxide in 2 × 10−4 M aqueous solutions of adenine (A), adenosine (Ado) and adenosine-5'-diphosphate (ADP)...     

The static and dynamic properties of PuCoGa5 and NpCoGa5 investigated by neutron scattering experiments

Neutron scattering results on single crystals shed light on the static and dynamic properties of the superconductor () PuCoGa₅ and its isostructural but antiferromagnetic () homologue NpCoGa₅. By polarized neutron diffraction the magnetization density in the paramagnetic state of both compounds has been inferred. The microscopic magnetization of NpCoGa₅ is consistent with the orbital and spin components of a localized Np³⁺ magnetic moment. In the case of PuCoGa₅ the microscopic magnetization is small, temperature-independent and cannot be described as a localized Pu³⁺ magnetic moment. For NpCoGa₅ a dynamic magnetic signal has been observed by three-axis spectroscopy in the antiferromagnetically ordered state. The magnetic signal is strongest at the antiferromagnetic zone center and an energy transfer of about 5 meV. Magnetic fluctuations persist at this position in the paramagnetic state. The dynamic response is similar to the dynamic response observed in other actinide intermetallic compounds. This supports the possibility that magnetic fluctuations could also be present in the paramagnetic superconductor PuCoGa₅.     

Charakterisierung von Austauschern mit cyclischen Polyethern als Ankergruppen durch Pyrolyse-Gas-Chromatographie und Pyrolyse-Massenspektrometrie

Zusammenfassung Pyrolyse-Gas-Chromatogramme und Pyrolyse-Massenspektren von Austauschern mit cyclischen Polyethern als Ankergruppen gestatten eine einfache und eindeutige Charakterisierung dieser Polymere. Aussagen über Herstellungsart des Austauschers, Einbau und Art der Ankergruppe sowie Vernetzungsgrad erhält man aus den katalogisierten Fingerprintspektren.Über die vorliegenden Ergebnisse kann der Syntheseweg der Austauscher beurteilt werden. Die polykondensierten Austauscher sind durchweg hoch vernetzt. Die Substituenten eines Hilfsvernetzers beeinflussen den Vernetzungsgrad stark. Substitutionsreaktionen von cyclischen Polyethern mit chlormethyliertem Polystyrol finden höchstens zu 66 % statt. Divinylbenzol ist als Vernetzer für vinylierte cyclische Polyether wenig geeignet. Bei der Polymerisation voluminöser Baugruppen muß ein der Größe angepaßter Vernetzer gewählt werden.

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Characterisation of exchangers with cyclic polyethers as anchor groups by pyrolysis gas-chromatography and pyrolysis mass-spectrometry

Summary Pyrolysis gas-chromatography and pyrolysis mass-spectrometry make possible a simple and definite characterisation of these polymers. The catalogued fingerprint spectra provide information about the method of preparation of the exchanger, the nature and the attachment of the anchor groups to the matrix as well as about the degree of cross-linkage.The results given allow a measurement of the efficiency of the synthesis. All the exchangers produced by polycondensation are highly cross-linked. The degree of cross-linkage is strongly influenced by the substituents of an additional cross-linking reagent. The highest yield for the reaction of cyclic polyethers with chloromethylated polystyrene is 66 %. Divinylbenzene is not suitable as a cross-linking reagent for vinylated cyclic polyethers. For bulky groups a cross-linking reagent of appropriate size has to be used.

Für finanzielle Unterstützung danken wir der Deutschen Forschungsgemeinschaft, Bonn-Bad Godesberg.     

The use of membranes in studies of reaction kinetics: arsenite catalysis of co2 hydration

The second-order catalytic rate constant for the industrially important CO₂ hydration catalyst, arsenite, has been determined using a novel membrane technique. The kinetic method involves the measurement of the steady-state flux of tagged CO₂ through an iramobilized liquid layer held within a thin, porous membrane; the liquid contains the catalyst and a basic buffer, sodium bicarbonate. The tracer flux is described by a set of linear equations, the solution of which yields the flux in terms of two dimensionless groups containing the kinetic and transport properties of the membrane phase. Experimental results agree with literature values on arsenite catalysis. The method is simple, accurate, and requires a minimum quantity of catalyst; it may have considerable applicability in studies of solution kinetics.     

Resonant enhancements at nonmagnetic ions: new possibilities for magnetic X-ray scattering

Synchrotron experiments with uranium antiferromagnetic compounds have discovered large ( >1000) enhancements of the magnetic scattering intensities at the K edges of nominally nonmagnetic anions, e.g., Ga and As. The width in energy, the position with respect to the white line, and the azimuthal and polarization dependencies permit one to associate the signal with transitions of E1 dipole symmetry from 1s to 4p states. In momentum space, the signal exhibits long-range order at the antiferromagnetic wave vector. We discuss possible channels capable of generating the observed enhancements.     

The magnetic phase diagram of the up-USe system

The magnetic phase diagram of the UP-USe solid solution was determined using neutron diffraction and magnetic susceptibility data obtained from polycrystalline samples. The lattice constants obey Vegard's Law. As the Se content increases magnetic phases with long periodicity gradually appear. The characteristic for UP magnetic structure (type I) consisting of ferromagnetic sheets stacked in the sequence +-+- is replaced by the type IA structure, ++--, which is stable over a fairly large composition range. A new phase transition called “step-like” is observed in this composition range at about 0.5T_N in both the neutron diffraction and the susceptibility data. In the UP_0.76Se_0.24 sample the type IA phase transforms to a new magnetic phase consisting of ferromagnetic sheets stacked nearly in the sequence +++--- or (3+, 3-). The repeat distance in real space is almost 3 chemical unit cells in one direction and the neutron diffraction data suggests that the square wave modulation is not fully developed. For compositions close to UP_0.70Se_0.30 the (3+,3-) type magnetic ordering coexists with ferromagnetism at low temperatures. The latter is the only magnetic phase obseved in compositions with more than 30 mol% of USe. Magnetization measurements performed at field strengths up to 5 T show that the samples with Se content around 30 mol% of USe exhibit typical metamagnetic behavior.     

Magnetic ground state of pure and doped CeFe2

A combination of neutron elastic and inelastic, resonant x-ray scattering, and 57Fe M?ssbauer experiments are used to determine the unusual magnetic ground state of CeFe2. The complementarities between different time-scale techniques may allow one to understand the dynamic features of the ground state in CeFe2 and its pseudobinary compounds, and how the frustration of Fe tetrahedra leads the appearance of antiferromagnetic fluctuations in the presence of ferrimagnetism. The resulting model can be used to rationalize many of the unusual and conflicting experimental results reported for this material in the literature.     

An electromagnetic calorimeter for the silicon detector concept

A silicon-tungsten calorimeter for silicon detector (SiD) at the International Linear Collider is under development. Recent progress is summarized.