Dynamic changes of Au/ZnO catalysts during methanol synthesis: A model study by temporal analysis of products (TAP) and Zn L_III near Edge X-Ray absorption spectroscopy

Small gold nanoparticles supported on ZnO have been identified as highly active and selective catalysts for the green synthesis of methanol from CO2 and H2. Furthermore, they can serve also a model system for the mechanistic understanding of methanol synthesis on the industrial Cu/ZnO catalyst. The dynamic changes in the structure of Au/ZnO upon exposure to methanol synthesis gas mixtures were studied using a combination of TAP reactor and near edge X-ray absorption spectroscopy (XANES) measurements at the Zn LIII edge, both in CO2/H2 and CO/H2 gas mixtures. TAP measurements indicated that CO can create significant amounts of O-vacancy defects in ZnO at 240°C, while CO2 can re-oxidize a pre-reduced catalyst or maintain this state in the presence of s trongly reducing gases (CO and H2). Furthermore, CO2 present as reactant or resulting from the reactive removal of surface lattice oxygen by interaction with CO can be deposited on the pre-reduced Au/ZnO surface as stable adsorbed carbon containing species, e.g., as surface carbonates, which decompose at T≥250°C. In situ XANES measurements at the Zn LIII edge revealed that ZnO is significantly reduced during reaction, both in CO2/H2 and CO/H2 gas mixtures, but with the extent of the reduction being more pronounced in CO/H2 than in CO2/H2. These results will be critically discussed in the light of previous findings on the role of ZnO reduction in the activity of methanol synthesis catalysts

Investigation of Electrocatalysts Produced by a Novel Thermal Spray Deposition Method

Common methods to produce supported catalysts include impregnation, precipitation, and thermal spray techniques. Supported electrocatalysts produced by a novel method for thermal spray deposition were investigated with respect to their structural properties, elemental composition, and electrochemical performance. This was done using electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Various shapes and sizes of catalyst particles were found. The materials exhibit different activity towards oxidation and reduction of Fe. The results show that this preparation method enables the selection of particle coverage as well as size and shape of the catalyst material. Due to the great variability of support and catalyst materials accessible with this technique, this approach is a useful extension to other preparation methods for electrocatalysts

Strong Metal Support Interaction as a Key Factor of Au Activation in CO Oxidation

We address the question of the nature of Au NP activation and through a combination of experimental and theoretical techniques. In situ XPS measurements of Au TiO2 during CO oxidation show high catalytic activity can be associated with the formation of an ionic Au species. DFT calculations performed on Au TiO2 show that the formation of such ionic Au is due to a strong metal support interaction between Au and reduced and defective TiO2. TEM supports these findings, indicating the formation of an overlayer of transition metal oxide support on Au NPs after CO oxidation. These results suggest TiO2 lattice oxygen is involved directly in CO oxidation, which was confirmed with labeled 18O2 experiment

Ein aktiver und stabiler Cobaltkatalysator für die Sauerstoffentwicklungsreaktion: Polymerisation einer ionischen Flüssigkeit

Inspiriert durch die katalytischen Eigenschaften von Single-site-Katalysatoren und der erhöhten Leistungsfähigkeit von Metallkatalysatoren durch ionische Flüssigkeiten wurde eine Methode zur gezielten und skalierbaren Platzierung von einzelnen Cobaltatomen auf Kohlenstoffnanoröhrenoberflächen mithilfe einer polymerisierten ionischen Flüssigkeit entwickelt. Durch eine ionische Flüssigkeit wurden einzelne, fein verteilte Cobaltionen koordiniert und als heterogener Katalysator für die Sauerstoffententwicklungsreaktion (OER) genutzt. Die erhaltenen Daten zeigen eine hohe Aktivität bei gleichzeitig vorhandener Stabilität

Are Au nanoparticles on oxygen free supports catalytically active?

Gold nanoparticles Au NPs on oxygen free supports were examined using near ambient pressure X ray photoelectron spectroscopy NAP XPS under CO oxidation conditions, and ex situ using scanning electron microscopy SEM and transmission electron microscopy TEM . Our observations demonstrate that Au NPs supported on carbon materials are inactive, regardless of the preparation method. Ozone O3 treatment of carbon supports leads oxygen functionalization of the supports. When subsequently exposed to a CO feed, CO is oxidized by the functionalized sites of the carbon support via a stoichiometric pathway. Microscopy reveals that the reaction with CO does not change the morphology of the Au NPs. In situ XPS reveals that the O3 treatment gives rise to additional Au 4f and O 1s peaks at binding energies of 85.25 85.6 eV and 529.4 530 eV, respectively, which are assigned to the presence of Au oxide. A surface oxide phase is formed during the activation of Au NPs supported on Au foil by O3 treatment. However, this phase decomposes in vacuum and the remaining low coordinative atoms do not have sufficient catalytic properties to oxidize CO, so the size reduction of Au NPs and or oxidation of Au NPs is not sufficient to activate A

Assessment of bone quality by the technique of multispiral computer tomography in patients with chronic osteomyelitis

Purpose - to study the roentgenomorphological features of the lower limb long bones in patients with chronic osteomyelitis using the technique of multi-spiral computer tomography (MSCT), and to propose the complex of parameters to assess bone quality. Material and methods. Roentgenography and computer tomography of the hips were performed in 49 patients with chronic osteomyelitis of long bones of lower extremities. The studies made using computer tomographs GE Light Speed VCT, Toshiba Aquilion-64, Somatom Smile. Results. The changes in bone structure of proximal femur were characterized by extremely marked polymorphism, and they almost didn’t repeat in the anatomical component. The cortical plate had heterogenous structure with resorption zones in the area of its transfer to the shaft. The character of roentgenomorphological changes in the shaft was individual in all the patients, but there were common manifestations as well which consisted in thickening of the cortical plate, different intensity of periosteal and endosteal layers. The cortical plate was significantly different in density, which exceeded 1700 HU in some places. When osteomyelitic process localized in the knee marked changes affected its all components, they manifested themselves in extended osteoporosis and local osteosclerosis. When osteomyelitic process localized in proximal tibia extensive resorption zones observed, the cortical plate thinned in proximal parts, its density was not more than 350 HU. Conclusion. The data demonstrated that bone quality in patients with chronic osteomyelitis had significant deviations from normal values in terms of changing both its density and architectonics. The deviations consisted in bone density decrease in the meta-epiphyseal part regardless of the process localization, in highly variable density values of the cortical plate as a result of its thickening or thinning, presence of resorption or sclerosis areas

Effect of Synthetic Auxin Analogs (2.4-D and α-NAA) on Growth and Biosynthetic Characteristics of Suspension Cell Culture of Tribulus terrestris L.

Abstract: Effect of synthetic analogs of auxins—2.4-dichlorophenoxyacetic (2.4-D) and α-naphthylacetic (α-NAA) acids—on growth characteristics and accumulation of steroidal glycosides was investigated in suspension cell culture of Tribulus terrestris L. It was found that the substitution of α-NAA for 2.4-D in the nutrient medium brought about a rise in the content of steroidal glycosides in the cultured cells (up to six times) and broadened their structural diversity (nine identified oligofurostanosides when growing culture on the medium with α-NAA vs. five compounds on the medium with 2.4-D). Positive influence of α-NAA exerted on biosynthetic characteristics of T. terrestris suspension cell culture was accompanied by changes in cell morphology (cytodifferentiation), the extent of their aggregation, and gradual decrease (during 3–4 cycles of growing) in culture viability up to its extinction. Simultaneous presence of both synthetic analogs of auxins (α-NAA and 2.4-D) in the growing medium also caused a rise in the content of steroidal glycosides in the cells of T. terrestris, although it was less pronounced (up to three times); however, the culture showed a relatively steady growth and great viability in this case. It was concluded that these two auxin analogs differently influenced the growth of plants’ cells in vitro and biosynthesis of substances of specialized metabolism, 2.4-D promoted cell proliferation, whereas α-NAA induced cytodifferentiation and activated the production of secondary compounds. This conclusion is corroborated by the data concerning plant cell cultures of other species of medicinal plants accumulating secondary metabolites from other groups. For instance, in the experiments with suspension cell culture of Panax ginseng C.A. Mey., substitution in the growth medium of α-NAA for 2.4-D brought about a rise in the content and diversity of triterpene glycosides (ginsenosides) associated with an elevated cell aggregation and deterioration of culture’s viability. Comparison of production of steroidal glycosides in plant cell cultures of T. terrestris and Dioscorea deltoidea Wall. that is grown for more than 40 years has shown that both cultures accumulated only furostanol (rather than spirostanol) glycosides that promoted cell proliferation. In suspension cell culture of Dioscorea, a high level of oligofurostanosides (up to 12% of dry biomass) was accumulated when growing culture on the medium with 2.4-D. Thus, investigation into the production of furostanol glycosides in plant cultured cells points to a multifactor system of regulation of secondary metabolism in vitro. Different synthetic auxin analogs may exert alternative influences on growth and biosynthetic processes. At the same time, prolonged culturing leads to an autoselection of cells with the properties promoting proliferation, specifically, with a high content of furostanol glycosides. © 2020, Pleiades Publishing, Ltd.This work was supported by the Russian Science Foundation, project no. 19-14-00387

Near Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd Au HOPG Catalysts The Effect of the Metal Ratio

In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite HOPG supported bimetallic Pd Au catalysts towards the CO oxidation based on the Pd Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu 2 sample with a lower Pd Au surface ratio 0.75 was already active at temperatures less than 150 C, while the PdAu 1 sample with a higher Pd Au surface ratio 1.0 became active only at temperatures above 200 C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near surface regions of the two component Pd Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmospher

SRPES and STM data for the model bimetallic Pd In HOPG catalysts Effects of mild post synthesis oxidative treatments

Post synthesis treatment of bimetallic catalysts in different gas phases resulting in the adsorption induced segregation is among promising approaches to enhance their activity not compromising selectivity towards a number of low temperature reactions. Our recently published paper M.A. Panafidin, A.V. Bukhtiyarov, I.P. Prosvirin, I.A. Chetyrin, A.Yu. Klyushin, A. Knop Gericke, N.S. Smirnova, P.V. Markov, I.S. Mashkovsky, Y.V. Zubavichus, A.Yu. Stakheev, V.I. Bukhtiyarov, A mild post synthesis oxidative treatment of Pd In HOPG bimetallic catalysts as a tool of their surface structure fine tuning. Appl. Surf. Sci. reports on Pd In intermetallic formation regularities and their evolution after storage in air as well as during treatment in oxygen at submillibar pressures. The current paper gives an extended representation of experimental ex situ in situ synchrotron based photoelectron spectroscopy SRPES and scanning tunnelling microscopy STM data used to derive scientific conclusions in the paper quoted abov

INFLUENCE OF THE PEOPLE SURPLUS MOISTENING AND FLOODING LANDSCAPE OF STAVROPOLISKIY EDGES

They аre аnalysed material influence of the person loads on agricultural lands in Stavropoliskiy region