Langerhans cell precursors initially arise from yolk sac progenitors, but are later superseded by fetal liver monocytes.

Active centers in Cu/SSZ-13 selective catalytic reduction (SCR) catalysts have been recently identified as isolated Cu and [Cu(OH)] ions. A redox reaction mechanism has also been established, where Cu ions cycle between Cu and Cu oxidation states during SCR reaction. While the mechanism for the reduction half-cycle (Cu → Cu) is reasonably well-understood, that for the oxidation half-cycle (Cu → Cu) remains an unsettled debate. Herein we report detailed reaction kinetics on low-temperature standard NH-SCR, supplemented by DFT calculations, as strong evidence that the low-temperature oxidation half-cycle occurs with the participation of two isolated Cu ions via formation of a transient [Cu(NH)]-O-[Cu(NH)] intermediate. The feasibility of this reaction mechanism is confirmed from DFT calculations, and the simulated energy barrier and rate constants are consistent with experimental findings. Significantly, the low-temperature standard SCR mechanism proposed here provides full consistency with low-temperature SCR kinetics.

We investigated the electron-pairing mechanism in an iron-based superconductor, iron selenide (FeSe), using scanning tunneling microscopy and spectroscopy. Tunneling conductance spectra of stoichiometric FeSe crystalline films in their superconducting state revealed evidence for a gap function with nodal lines. Electron pairing with twofold symmetry was demonstrated by direct imaging of quasiparticle excitations in the vicinity of magnetic vortex cores, Fe adatoms, and Se vacancies. The twofold pairing symmetry was further supported by the observation of striped electronic nanostructures in the slightly Se-doped samples. The anisotropy can be explained in terms of the orbital-dependent reconstruction of electronic structure in FeSe.

Cu/SSZ-13 catalysts with three Si/Al ratios of 6, 12 and 35 were synthesized with Cu incorporation via solution ion exchange. The implications of varying Si/Al ratios on the nature of the multiple Cu species that can be present in the SSZ-13 zeolite are a major focus of this work, as highlighted by the results of a variety of catalyst characterization and reaction kinetics measurements. Specifically, catalysts were characterized with surface area/pore volume measurements, temperature programmed reduction by H 2 (H 2-TPR), NH 3 temperature programmed desorption (NH 3-TPD), and DRIFTS and solid-state nuclear magnetic resonance (NMR) spectroscopies. Catalytic properties were examined using NO oxidation, ammonia oxidation, and standard ammonia selective catalytic reduction (NH 3-SCR) reactions on selected catalysts under differential conditions. Besides indicating the possibility of multiple active Cu species for these reactions, the measurements are also used to untangle some of the complexities caused by the interplay between redox of Cu ion centers and Brønsted acidity. All three reactions appear to follow a redox reaction mechanism, yet the roles of Brønsted acidity are quite different. For NO oxidation, increasing Si/Al ratio lowers Cu redox barriers, thus enhancing reaction rates. Brønsted acidity appears to play essentially no role for this reaction. For standard NH 3-SCR, residual Brønsted acidity plays a significant beneficial role at both low-and high-temperature regimes. For NH 3 oxidation, no clear trend is observed suggesting both Cu ion center redox and Brønsted acidity play important and perhaps competing roles.