Nanoporous Au/Ag Catalyzed Benzylic sp3C−H Oxidation of 9H-Fluorene Derivatives and Similar Molecules with TBHP

Nanoporous gold (npAu) was tested as a catalyst for oxidations of various benzylic sp3-carbon positions in 9H-fluorene derivatives and similar hydrocarbons using tertbutyl hydroperoxide (TBHP) as an oxidant. The silver content in the npAu catalyst had a major influence on the overall conversion: Lower silver amounts (0.53 mol%) led to higher conversions, whereas higher amounts of silver increasingly resulted in the disproportionation of TBHP as a competing reaction. Because residual silver from the bulk alloy was oxidized by TBHP and leached into the solution during the reaction, the Ag content diminished over time. Therefore, the recycling of the catalyst had a positive effect on the conversion after each use. Using electron paramagnetic resonance (EPR) spectroscopy, the formation of radicals from TBHP by npAu was evidenced indicating a radical-based reaction mechanism which was further elucidated by NMR spectroscopic and GC-MS (trace) product analysis. Subsequent oxidations of benzylic sp3-carbon positions gave good to excellent conversions and chemoselectivities featuring npAu as a suitable catalyst for such reactions

Heterogeneity of oxygen reactivity: key for selectivity of partial methanol oxidation on gold surfaces

Recent evidence for low-temperature oxidation of methyl formate on Au(332) may affect the selectivity of gold catalysts during partial oxidation of methanol. Under isothermal conditions, overoxidation of methyl formate is significantly slower than methanol oxidation which can be attributed to special oxygen species required for overoxidation

Methanol oxidation on Au(332): methyl formate selectivity and surface deactivation under isothermal conditions

Methanol oxidation on the stepped Au(332) surface was investigated by pulsed isothermal molecular beam (MB) experiments. The effect of the surface temperature as well as the influence of changes in the methanol and atomic oxygen flux on the partial oxidation to methyl formate was studied. A maximum in methyl formate formation is observed at 250 K under the applied single collision conditions. Increasing the methanol to oxygen ratio was found to increase the selectivity to methyl formate and decrease unwanted overoxidation to surface deactivating formate detected by in situ infrared reflection absorption spectroscopy (IRAS). The results show evidence for the importance of an additional deactivation mechanism for methyl formate formation connected to methanol which is active under oxygen-deficient conditions at low temperatures. Moreover, the measurements suggest a small number of sites to be highly reactive for methyl formate formation which are preferentially blocked under oxygen-deficient conditions

A quantitative microscopic view on the gas-phase-dependent phase transformation from tetragonal to monoclinic ZrO2

ZrO2 is a versatile material with diverse applications, including structural ceramics, sensors, and catalysts. The properties of ZrO2 are largely determined by its crystal structure, which is temperature- and atmosphere dependent. Thus, this work focuses on a quantitative analysis of the temperature- and gas atmosphere-dependent phase transformation of tetragonal t-ZrO2 into monoclinic m-ZrO2 during heating–cooling cycles from room temperature to 1273 K. Synchrotron-based in situ X-ray diffraction (XRD) studies in gas atmospheres of different reduction strengths, namely, 5 vol% H2/Ar, He, CO2, and air, revealed a stabilizing effect of inert and reductive environments, directly yielding different temperature onsets in the phase transformation during cooling (i.e., 435, 510, 710, and 793 K for 5 vol% H2/Ar, He, CO2, and air, respectively). Rietveld refinement shows a direct influence of the atmosphere on grain size, unit cell, and weight fraction of both polymorphs in the product composite matrix. The tetragonal-to-monoclinic (t–m) phase transformation is suppressed in the sample heated only up to ∼850 K, independent of the gas atmosphere. The results of ex situ XRD, transmission electron microscopic, electron paramagnetic resonance, and oxygen titration experiments confirmed that the phase transformation is accompanied by a change in the crystallite/particle size and the amount of lattice defects (i.e., oxygen vacancy). Due to the different onset temperatures, a complex interplay between kinetic limitations of phase transformation and grain sintering yields different pathways of the phase transformation and, eventually, very different final crystallite sizes of both t-ZrO2 and m-ZrO2

Partial Oxidation of Methanol on Gold: How Selectivity Is Steered by Low-Coordinated Sites

Partial methanol oxidation proceeds with high selectivity to methyl formate (MeFo) on nanoporous gold (npAu) catalysts. As low-coordinated sites on npAu were suggested to affect the selectivity, we experimentally investigated their role in the isothermal selectivity for flat Au(111) and stepped Au(332) model surfaces using a molecular beam approach under well-defined conditions. Direct comparison shows that steps enhance desired MeFo formation and lower undesired overoxidation. DFT calculations reveal differences in oxygen distribution that enhance the barriers to overoxidation at steps. Thus, these results provide an atomic-level understanding of factors controlling the complex reaction network on gold catalysts, such as npAu

Selective Oxidation of Methanol to Methyl Formate on Gold: The Role of Low-Coordinated Sites Revealed by Isothermal Pulsed Molecular Beam Experiments and AIMD Simulations

To elucidate the role of low-coordinated sites in the partial methanol oxidation to methyl formate (MeFo), the isothermal reactivity of flat Au(111) and stepped Au(332) in pulsed molecular beam experiments was compared for a broad range of reaction conditions. Low-coordinated step sites were found to enhance MeFo selectivity, especially at low coverage conditions, as found at higher temperatures. The analysis of the transient kinetics provides evidence for the essential role of AuxOy phases for MeFo formation and the complex interplay of different oxygen species for the observed selectivity. Ab initio molecular dynamic simulations yielded microscopic insights in the formation of AuxOy phases on flat and stepped gold surfaces emphasizing the role of low-coordinated sites in their formation. Moreover, associated surface restructuring provides atomic-scale insights which align with the experimentally observed transient kinetics in MeFo formation

IL10-Deficiency in CD4+ T Cells Exacerbates the IFNγ and IL17 Response During Bacteria Induced Colitis

Background/Aims: IL10 is a key inhibitor of effector T cell activation and a mediator of intestinal homeostasis. In addition, IL10 has emerged as a key immunoregulator during infection with various pathogens, ameliorating the excessive T-cell responses that are responsible for much of the immunopathology associated with the infection. Because IL10 plays an important role in both intestinal homeostasis and infection, we studied the function of IL10 in infection-associated intestinal inflammation. Methods: Wildtype mice and mice deficient in CD4+ T cell-derived or regulatory T cells-derived IL10 were infected with the enteric pathogen Citrobacter (C.) rodentium and analyzed for the specific immune response and pathogloy in the colon. Results: We found that IL10 expression is upregulated in colonic tissue after infection with C. rodentium, especially in CD4+ T cells, macrophages and dendritic cells. Whereas the deletion of IL10 in regulatory T cells had no effect on C. rodentium induced colitis, infection of mice deficient in CD4+ T cell-derived IL10 exhibited faster clearance of the bacterial burden but worse colitis, crypt hyperplasia, and pathology than did WT mice. In addition, the depletion of CD4+ T cell-derived IL10 in infected animals was accompanied by an accelerated IFNγ and IL17 response in the colon. Conclusion: Thus, we conclude that CD4+ T cell-derived IL10 is strongly involved in the control of C. rodentium-induced colitis. Interference with this network could have implications for the treatment of infection-associated intestinal inflammation

Transition-Metal-Doping of CaO as Catalyst for the OCM Reaction, a Reality Check

In this study, first-row transition metal-doped calcium oxide materials (Mn, Ni, Cr, Co., and Zn) were synthesized, characterized, and tested for the OCM reaction. Doped carbonate precursors were prepared by a co-precipitation method. The synthesis parameters were optimized to yield materials with a pure calcite phase, which was verified by XRD. EPR measurements on the doped CaO materials indicate a successful substitution of Ca2+ with transition metal ions in the CaO lattice. The materials were tested for their performance in the OCM reaction, where a beneficial effect towards selectivity and activity effect could be observed for Mn, Ni, and Zn-doped samples, where the selectivity of Co- and Cr-doped CaO was strongly reduced. The optimum doping concentration could be identified in the range of 0.04-0.10 atom%, showing the strongest decrease in the apparent activation energy, as well as the maximum increase in selectivity

Nuclear spin ratios of deuterated ammonia in prestellar cores. LAsMA observations of H-MM1 and Oph D

We determine the ortho/para ratios of NH2D and NHD2 in two dense, starless cores, where their formation is supposed to be dominated by gas-phase reactions, which, in turn, is predicted to result in deviations from the statistical spin ratios. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of these molecules were derived employing 3D radiative transfer modelling, using different assumptions about the abundance profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton or deuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed spin ratios. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of their statistical values 3 and 2, respectively, and taking 3-sigma limits, deviations from these of about 20% are allowed. Of the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed abundances and spin ratios. The nuclear spin ratios derived here are in contrast with spin-state chemistry models that assume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The efficiency of chemical desorption influences strongly the predicted abundances of NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.Comment: accepted for publication in Astronomy & Astrophysic

Cobalt-substituted porous calcium copper titanate electrodes for paracetamol degradation by an electro-oxidation/peroxymonosulfate system

Developing cobalt-substituted perovskite electroactive membranes with an efficient Co/Cu combination mode is an important environmental challenge for removing drugs via peroxymonosulfate (PMS) activation. In this work, cobalt (Co)-substituted calcium copper titanatewas synthesized with an easy ball milling process and used as an anode in electro-oxidation in the presence of PMS for paracetamol degradation. The Co-CCTO anode with a Co ratio of 0.5 showed the highest removal efficiency (100 % of 10 ppm paracetamol after 180 min) due to the increase of the active sites and the appearance of the Co2+/Co3+ cycle that accelerates the charge transfer with Co incorporation into the lattice. Scavenger experiments showed that sulfate radicals (SO4̇−), oxygen radicals (O2̇-), hydroxyl radicals (̇OH), and singlet oxygen (1O2) were generated in the electro-oxidation-PMS reaction system and that SO4̇−, 1O2, and O2̇- were the dominant active radicals. The toxicity tests with Vibrio fischeri confirmed paracetamol mineralization and decomposition and the elimination of harmful by-products. It is crucial to explore the substitution of CCTO with different metal dopants in order to optimize the membrane performance and overcome the limitations associated with cobalt substitution