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Thermally Induced Surface Structure and Morphology Evolution in Bimetallic Pt-Au/HOPG Nanoparticles as Probed Using XPS and STM. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 14:57. [PMID: 38202512 PMCID: PMC10780797 DOI: 10.3390/nano14010057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 12/18/2023] [Accepted: 12/21/2023] [Indexed: 01/12/2024]
Abstract
Bimetallic nanoparticles expand the possibilities of catalyst design, providing an extra degree of freedom for tailoring the catalyst structure in comparison to purely monometallic systems. The distribution mode of two metal species defines the structure of surface catalytic sites, and current research efforts are focused on the development of methods for their controlled tuning. In light of this, a comprehensive investigation of the factors which influence the changes in the morphology of bimetallic nanoparticles, including the elemental redistribution, are mandatory for each particular bimetallic system. Here we present the combined XPS/STM study of the surface structure and morphology of bimetallic Pt-Au/HOPG nanoparticles prepared by thermal vacuum deposition and show that thermal annealing up to 350 °C induces the alloying process between the two bulk-immiscible metal components. Increasing the treatment temperature enhances the extent of Pt-Au alloying. However, the sintering of nanoparticles starts to occur above 500 °C. The approach implemented in this work includes the theoretical simulation of XPS signal intensities for a more meticulous analysis of the compositional distribution and can be helpful from a methodological perspective for other XPS/STM studies of bimetallic nanoparticles on planar supports.
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Reductive Transformation of O-, N-, S-Containing Aromatic Compounds under Hydrogen Transfer Conditions: Effect of the Process on the Ni-Based Catalyst. Molecules 2023; 28:7041. [PMID: 37894520 PMCID: PMC10609389 DOI: 10.3390/molecules28207041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Revised: 10/09/2023] [Accepted: 10/10/2023] [Indexed: 10/29/2023] Open
Abstract
The influence of the reaction medium on the surface structure and properties of a Ni-based catalyst used for the reductive transformations of O-, N-, and S-containing aromatic substrates under hydrogen transfer conditions has been studied. The catalysts were characterized by XRD, XPS, and IR spectroscopy and TEM methods before and after the reductive reaction. It has been shown that the conversion of 1-benzothiophene causes irreversible poisoning of the catalyst surface with the formation of the Ni2S3 phase, whereas the conversion of naphthalene, 1-benzofuran, and indole does not cause any phase change of the catalyst at 250 °C. However, after the indole conversion, the catalyst surface remains enriched with N-containing compounds, which are evenly distributed over the surface.
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Combining Atomic Layer Deposition with Surface Organometallic Chemistry to Enhance Atomic-Scale Interactions and Improve the Activity and Selectivity of Cu-Zn/SiO 2 Catalysts for the Hydrogenation of CO 2 to Methanol. JACS AU 2023; 3:2536-2549. [PMID: 37772188 PMCID: PMC10523371 DOI: 10.1021/jacsau.3c00319] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Revised: 08/08/2023] [Accepted: 08/09/2023] [Indexed: 09/30/2023]
Abstract
The direct synthesis of methanol via the hydrogenation of CO2, if performed efficiently and selectively, is potentially a powerful technology for CO2 mitigation. Here, we develop an active and selective Cu-Zn/SiO2 catalyst for the hydrogenation of CO2 by introducing copper and zinc onto dehydroxylated silica via surface organometallic chemistry and atomic layer deposition, respectively. At 230 °C and 25 bar, the optimized catalyst shows an intrinsic methanol formation rate of 4.3 g h-1 gCu-1 and selectivity to methanol of 83%, with a space-time yield of 0.073 g h-1 gcat-1 at a contact time of 0.06 s g mL-1. X-ray absorption spectroscopy at the Cu and Zn K-edges and X-ray photoelectron spectroscopy studies reveal that the CuZn alloy displays reactive metal support interactions; that is, it is stable under H2 atmosphere and unstable under conditions of CO2 hydrogenation, indicating that the dealloyed structure contains the sites promoting methanol synthesis. While solid-state nuclear magnetic resonance studies identify methoxy species as the main stable surface adsorbate, transient operando diffuse reflectance infrared Fourier transform spectroscopy indicates that μ-HCOO*(ZnOx) species that form on the Cu-Zn/SiO2 catalyst are hydrogenated to methanol faster than the μ-HCOO*(Cu) species that are found in the Zn-free Cu/SiO2 catalyst, supporting the role of Zn in providing a higher activity in the Cu-Zn system.
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CO 2 Methanation: Solvent-Free Synthesis of Nickel-Containing Catalysts from Complexes with Ethylenediamine. MATERIALS (BASEL, SWITZERLAND) 2023; 16:2616. [PMID: 37048912 PMCID: PMC10095988 DOI: 10.3390/ma16072616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 03/17/2023] [Accepted: 03/23/2023] [Indexed: 06/19/2023]
Abstract
CO2 methanation was studied in the presence of nickel catalysts obtained by the solid-state combustion method. Complexes with a varying number of ethylenediamine molecules in the coordination sphere of nickel were chosen as the precursors of the active component of the catalysts. Their synthesis was carried out without the use of solvents, which made it possible to avoid the stages of their separation from the solution and the utilization of waste liquids. The composition and structure of the synthesized complexes were confirmed by elemental analysis, IR spectroscopy, powder XRD and XPS methods. It was determined that their thermal decomposition in the combustion wave proceeds in multiple stages with the formation of NiO and Ni(OH)2, which are reduced to Ni0. Higher ethylenediamine content in the complex leads to a higher content of metal in the solid products of combustion. However, different ratios of oxidized and reduced forms of nickel do not affect the initial activation temperature of nickel catalysts in the presence of CO2. It was noted that, after activation, the sample obtained from [Ni(C2H8N2)2](NO3)2 exhibited the highest activity in CO2 methanation. Thus, this complex is a promising precursor for CO2 methanation catalysts, and its synthesis requires only a small amount of ethylenediamine.
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Synthesis of Boron-Doped Carbon Nanomaterial. MATERIALS (BASEL, SWITZERLAND) 2023; 16:1986. [PMID: 36903101 PMCID: PMC10004671 DOI: 10.3390/ma16051986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 02/01/2023] [Accepted: 02/25/2023] [Indexed: 06/18/2023]
Abstract
A new method for the synthesis of boron-doped carbon nanomaterial (B-carbon nanomaterial) has been developed. First, graphene was synthesized using the template method. Magnesium oxide was used as the template that was dissolved with hydrochloric acid after the graphene deposition on its surface. The specific surface area of the synthesized graphene was equal to 1300 m2/g. The suggested method includes the graphene synthesis via the template method, followed by the deposition of an additional graphene layer doped with boron in an autoclave at 650 °C, using a mixture of phenylboronic acid, acetone, and ethanol. After this carbonization procedure, the mass of the graphene sample increased by 70%. The properties of B-carbon nanomaterial were studied using X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and adsorption-desorption techniques. The deposition of an additional graphene layer doped with boron led to an increase of the graphene layer thickness from 2-4 to 3-8 monolayers, and a decrease of the specific surface area from 1300 to 800 m2/g. The boron concentration in B-carbon nanomaterial determined by different physical methods was about 4 wt.%.
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Effect of Reductive Treatment Duration on the Structure and Properties of Pd‐Zn/C Catalysts for Liquid‐Phase Acetylene Hydrogenation. ChemCatChem 2022. [DOI: 10.1002/cctc.202200893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Effect of hydrogen reduction and palladium promotion of tungstate-modified zirconia on isomerization of heptane. MOLECULAR CATALYSIS 2022. [DOI: 10.1016/j.mcat.2022.112527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Atomic-scale changes of silica-supported catalysts with nanocrystalline or amorphous gallia phases: implications of hydrogen pretreatment on their selectivity for propane dehydrogenation. Catal Sci Technol 2022; 12:3957-3968. [PMID: 35814525 PMCID: PMC9208381 DOI: 10.1039/d2cy00074a] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 05/01/2022] [Indexed: 12/22/2022]
Abstract
This work explores how H2 pretreatment at 550 °C induces structural transformation of two gallia-based propane dehydrogenation (PDH) catalysts, viz. nanocrystalline γ/β-Ga2O3 and amorphous Ga2O3 (GaOx) supported on silica (γ-Ga2O3/SiO2 and Ga/SiO2, respectively) and how it affects their activity, propene selectivity and stability with time on stream (TOS). Ga/SiO2–H2 shows poor activity and propene selectivity, no coking and no deactivation with TOS, similar to Ga/SiO2. In contrast, the high initial activity and propene selectivity of γ-Ga2O3/SiO2–H2 decline with TOS but to a lesser extent than in calcined γ-Ga2O3/SiO2. In addition, γ-Ga2O3/SiO2–H2 cokes less than γ-Ga2O3/SiO2. Ga K-edge X-ray absorption spectroscopy suggests an increased disorder of the nanocrystalline γ/β-Ga2O3 phases in γ-Ga2O3/SiO2–H2 and the emergence of additional tetrahedral Ga sites (GaIV). Such GaIV sites are strong Lewis acid sites (LAS) according to studies using adsorbed pyridine and CO probe molecules, i.e., the abundance of strong LAS is higher in γ-Ga2O3/SiO2–H2 compared to γ-Ga2O3/SiO2 but lower than in Ga/SiO2 and Ga/SiO2–H2. Dissociation of H2 on the Ga–O linkages in γ-Ga2O3/SiO2–H2 yields high-frequency Ga–H bands that are observed in Ga/SiO2 and Ga/SiO2–H2 but not detected in γ-Ga2O3/SiO2. We attribute the increased amount of GaIV sites in γ-Ga2O3/SiO2–H2 mostly to an increased disorder in γ/β-Ga2O3. X-ray photoelectron spectroscopy detects the formation of Ga+ and Ga0 species in both Ga/SiO2–H2 and γ-Ga2O3/SiO2–H2. Therefore, it is likely that a minor amount of GaIV sites also forms through the interaction of Ga+ (such as Ga2O) and/or Ga0 with silanol groups of SiO2. We explore how H2 pretreatment changes the structure of two gallia-based propane dehydrogenation catalysts, viz. crystalline γ/β-Ga2O3 and amorphous Ga2O3 supported on silica, and how it affects their activity, selectivity and stability on stream.![]()
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SRPES and STM data for the model bimetallic Pd-In/HOPG catalysts: Effects of mild post-synthesis oxidative treatments. Data Brief 2021; 39:107626. [PMID: 34877389 PMCID: PMC8633860 DOI: 10.1016/j.dib.2021.107626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2021] [Revised: 11/09/2021] [Accepted: 11/18/2021] [Indexed: 11/28/2022] Open
Abstract
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 above.
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Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio. NANOMATERIALS 2021; 11:nano11123292. [PMID: 34947641 PMCID: PMC8703420 DOI: 10.3390/nano11123292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 12/01/2021] [Accepted: 12/02/2021] [Indexed: 11/16/2022]
Abstract
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 atmosphere.
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Investigation of concentration hysteresis in methane oxidation on bimetallic Pt–Pd/Al2O3 catalyst by in situ XPS and mass spectrometry. MENDELEEV COMMUNICATIONS 2021. [DOI: 10.1016/j.mencom.2021.09.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Redox reactions between acetonitrile and nitrogen dioxide in the interlayer space of fluorinated graphite matrices. Phys Chem Chem Phys 2021; 23:10580-10590. [PMID: 33903859 DOI: 10.1039/d0cp06412b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The interlayer space of 2D materials can be a slit reactor where transformations not typical for the gas phase occur. We report redox reactions involving acetonitrile and nitrogen oxide guests in galleries of fluorinated graphite. Fluorinated graphite intercalation compounds with acetonitrile are treated with dinitrogen tetraoxide and the synthesis products are studied by a set of experimental methods. Data analysis reveals that N2O4 dissociates in fluorinated graphite matrices to form nitrogen-containing species NO3, NO2, NO, and N2. The interaction of NO3 with acetonitrile yields HNO3, which predominates as a guest in the synthesis products independently of the fluorination degree of the matrix. This reaction is accompanied by the removal of fluorine atoms weakly bonded to the graphite layers, leading to partial defluorination of the matrices. Our work demonstrates the possibility of using fluorinated graphite as a test nanoreactor whose dimension can be controlled by fluorination of the layers.
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Influence of the active TaN/ZrO x /Ni memristor layer oxygen content on forming and resistive switching behavior. NANOTECHNOLOGY 2021; 32:185205. [PMID: 33620032 DOI: 10.1088/1361-6528/abce7b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The influence of oxygen content in active zirconium oxide layers on the electrophysical properties of TaN/ZrO x /Ni memristors is investigated. The [O]/[Zr] atomic ratio (x) in the oxide layers was varied in the range from 1.56 to 2.0 by changing the partial oxygen pressure during their deposition by ion-beam sputtering deposition. The ZrO x film compositions were analyzed using x-ray photoelectron spectroscopy and density functional theory simulations. The multiple resistive switching phenomenon in TaN/ZrO x /Ni memristors was found to occur in a certain range of x ≥ 1.78. With the x value decreasing in the oxide layers, the forming voltage of memristors decreased. Furthermore, at the lower edge of x values the switchable range, they no longer required forming. At the same time, as the x value decreased, the memory window (I ON/I OFF ratio) also decreased from 5 to 1 order of magnitude due to an increase in the memristor conductivity in the high resistance state. In order to identify the underlying conduction mechanism of TaN/ZrO x /Ni memristors, their current-voltage curves in low and high resistance states were analyzed in the temperature range from 250 to 400 K for the samples with x = 1.78 (forming-free) and 1.97 (which required forming). It was found that, for both samples, the conductivity in the low-resistance state is characterized by the trap-free space-charge-limited current (SCLC) model, whereas the conductivity in the high-resistance state is characterized by the trap-mediated SCLC model. The possible origins of structural defects involved in the memristor conductivity and resistive switching are discussed based on the obtained results.
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Electronic structure and charge transport mechanism in a forming-free SiO x -based memristor. NANOTECHNOLOGY 2020; 31:505704. [PMID: 33021224 DOI: 10.1088/1361-6528/abb505] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
THe memristor is a key memory element for neuromorphic electronics and new generation flash memories. One of the most promising materials for memristor technology is silicon oxide SiO x , which is compatible with silicon-based technology. In this paper, the electronic structure and charge transport mechanism in a forming-free SiO x -based memristor fabricated with the plasma enhanced chemical vapor deposition method is investigated. The experimental current-voltage characteristics measured at different temperatures in high-resistance, low-resistance and intermediate states are compared with various charge transport theories. The charge transport in all states is limited by the space charge-limited current model. The trap parameters, responsible for the charge transport in a SiO x -based memristor in different states, are determined.
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Effect of Organic Additives on the Structure and Hydrotreating Activity of a CoMoS/Multiwalled Carbon Nanotube Catalyst. Ind Eng Chem Res 2020. [DOI: 10.1021/acs.iecr.0c03915] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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New Multicomponent MoVSbNbCeO
x
/SiO
2
Catalyst with Enhanced Catalytic Activity for Oxidative Dehydrogenation of Ethane to Ethylene. ChemCatChem 2020. [DOI: 10.1002/cctc.202000489] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Zinc Addition Influence on the Properties of Pd/Sibunit Catalyst in Selective Acetylene Hydrogenation. Top Catal 2020. [DOI: 10.1007/s11244-019-01215-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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19
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Spatially resolved NMR spectroscopy of heterogeneous gas phase hydrogenation of 1,3-butadiene with parahydrogen. Catal Sci Technol 2020. [DOI: 10.1039/c9cy02100k] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Glass tube reactors with Pd, Pt, Rh or Ir nanoparticles dispersed on a thin layer of TiO2, CeO2, SiO2 or Al2O3 provided mechanistic insight into the hydrogenation of 1,3-butadiene using parahydrogen.
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CO-induced segregation as an efficient tool to control the surface composition and catalytic performance of PdAg3/Al2O3 catalyst. MENDELEEV COMMUNICATIONS 2019. [DOI: 10.1016/j.mencom.2019.09.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Cover Feature: Robust In Situ Magnetic Resonance Imaging of Heterogeneous Catalytic Hydrogenation with and without Hyperpolarization (ChemCatChem 3/2019). ChemCatChem 2019. [DOI: 10.1002/cctc.201900111] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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22
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Robust In Situ Magnetic Resonance Imaging of Heterogeneous Catalytic Hydrogenation with and without Hyperpolarization. ChemCatChem 2018. [DOI: 10.1002/cctc.201801820] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Nanoscale potential fluctuations in nonstoichiometrics tantalum oxide. NANOTECHNOLOGY 2018; 29:425202. [PMID: 30020078 DOI: 10.1088/1361-6528/aad430] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The atomic and electronic structure of nonstoichiometric amorphous tantalum oxide (TaO x ) films of different composition has been investigated by means of electron microscopy, x-ray photoelectron spectroscopy, Raman and infrared spectroscopy. The dispersion of the absorption coefficient and refraction index has been studied by spectral ellipsometry. The optical spectra were interpreted using the results of a quantum-chemical simulation for crystalline orthorhombic TaO x . It was found that the presence of oxygen vacancies in the oxygen-deficient TaO x film show an optical absorption peak at 4.6 eV. It has been established that TaO x consists of stoichiometric Ta2O5, metallic Ta clusters less than 20 nm in size, and tantalum suboxides TaO y (y < 2.5). The model of nanoscale potential fluctuations of TaO x bandgap in the range of 0-4.2 eV is proposed and justified. The design of the flash memory element based on the effect of localization of electrons and holes in Ta metallic nanoclusters in the TaO x matrix is proposed.
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Electronic structure of stoichiometric and oxygen-deficient ferroelectric Hf 0.5Zr 0.5O 2. NANOTECHNOLOGY 2018; 29:194001. [PMID: 29393855 DOI: 10.1088/1361-6528/aaacb1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The electronic structure of oxygen-deficient Hf0.5Zr0.5O2 in the non-centrosymmetric orthorhombic (ferroelectric) phase was investigated by means of x-ray photoelectron spectroscopy and first-principle density functional theory calculations. It was established that a peak in the photoelectron spectra observed at an energy above the valence band top of ferroelectric Hf0.5Zr0.5O2 in ion-etched samples was due to oxygen vacancies. A method for evaluating the oxygen vacancies concentration in the material from the comparison of experimental and theoretical photoelectron spectra of the valence band is proposed. It is found that oxygen polyvacancies are not formed in ferroelectric Hf0.5Zr0.5O2: an energy-favorable spatial arrangement of several oxygen vacancies in the crystal corresponds to the configuration formed by noninteracting vacancies distant from each other. The oxygen vacancies in five charged states were simulated. The electron levels in the bandgap caused by charged oxygen vacancies indicate that any type of oxygen vacancies in ferroelectric Hf0.5Zr0.5O2 can capture both electrons and holes, i.e. can act as an amphoteric localization center for charge carriers.
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PdZn/α-Al 2 O 3 catalyst for liquid-phase alkyne hydrogenation: effect of the solid-state alloy transformation into intermetallics. MENDELEEV COMMUNICATIONS 2018. [DOI: 10.1016/j.mencom.2018.03.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Frontispiece: Selective Single-Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen. Chemistry 2018. [DOI: 10.1002/chem.201881163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Charge Transport and the Nature of Traps in Oxygen Deficient Tantalum Oxide. ACS APPLIED MATERIALS & INTERFACES 2018; 10:3769-3775. [PMID: 29308879 DOI: 10.1021/acsami.7b16753] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Optical and transport properties of nonstoichiometric tantalum oxide thin films grown by ion beam deposition were investigated in order to understand the dominant charge transport mechanisms and reveal the nature of traps. The TaOx films composition was analyzed by X-ray photoelectron spectroscopy and by quantum-chemistry simulation. From the optical absorption and photoluminescence measurements and density functional theory simulations, it was concluded that the 2.75 eV blue luminescence excited in a TaOx by 4.45 eV photons, originates from oxygen vacancies. These vacancies are also responsible for TaOx conductivity. The thermal trap energy of 0.85 eV determined from the transport experiments coincides with the half of the Stokes shift of the blue luminescence band. It is argued that the dominant charge transport mechanism in TaOx films is phonon-assisted tunneling between the traps.
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Selective Single-Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen. Chemistry 2018; 24:2547-2553. [DOI: 10.1002/chem.201705644] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Indexed: 01/19/2023]
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Crystalline structure and magnetic properties of structurally ordered cobalt–iron alloys grown on Bi-containing topological insulators and systems with giant Rashba splitting. CrystEngComm 2018. [DOI: 10.1039/c8ce00326b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Structurally ordered metallic nanostructures on Bi-containing TI surfaces were obtained, with detailed studies of their crystalline structure and magnetic properties.
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Reversible Bulk Oxidation of Ni Foil During Oscillatory Catalytic Oxidation of Propane: A Novel Type of Spatiotemporal Self-Organization. PHYSICAL REVIEW LETTERS 2017; 119:026001. [PMID: 28753346 DOI: 10.1103/physrevlett.119.026001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Indexed: 06/07/2023]
Abstract
A novel type of temporal and spatial self-organization in a heterogeneous catalytic reaction is described for the first time. Using in situ x-ray photoelectron spectroscopy, gas chromatography, and mass spectrometry, we show that, under certain conditions, self-sustained reaction-rate oscillations arise in the oxidation of propane over Ni foil because of reversible bulk oxidation of Ni to NiO, which can be observed even with the naked eye as chemical waves propagating over the catalyst surface.
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The effect of oxidative and reductive treatments of titania-supported metal catalysts on the pairwise hydrogen addition to unsaturated hydrocarbons. Catal Today 2017. [DOI: 10.1016/j.cattod.2016.02.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Production of Pure Aqueous 13 C-Hyperpolarized Acetate by Heterogeneous Parahydrogen-Induced Polarization. Chemistry 2016; 22:16446-16449. [PMID: 27607402 PMCID: PMC5544125 DOI: 10.1002/chem.201603974] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Indexed: 12/18/2022]
Abstract
A supported metal catalyst was designed, characterized, and tested for aqueous phase heterogeneous hydrogenation of vinyl acetate with parahydrogen to produce 13 C-hyperpolarized ethyl acetate for potential biomedical applications. The Rh/TiO2 catalyst with a metal loading of 23.2 wt % produced strongly hyperpolarized 13 C-enriched ethyl acetate-1-13 C detected at 9.4 T. An approximately 14-fold 13 C signal enhancement was detected using circa 50 % parahydrogen gas without taking into account relaxation losses before and after polarization transfer by magnetic field cycling from nascent parahydrogen-derived protons to 13 C nuclei. This first observation of 13 C PHIP-hyperpolarized products over a supported metal catalyst in an aqueous medium opens up new possibilities for production of catalyst-free aqueous solutions of nontoxic hyperpolarized contrast agents for a wide range of biomolecules amenable to the parahydrogen induced polarization by side arm hydrogenation (PHIP-SAH) approach.
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The “direct” synthesis of trialkoxysilanes: New data for understanding the processes of the copper-containing active sites formation during the activation of the initial silicon based contact mass. J Catal 2016. [DOI: 10.1016/j.jcat.2016.03.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Cover Picture: Strong Metal-Support Interactions for Palladium Supported on TiO 2Catalysts in the Heterogeneous Hydrogenation with Parahydrogen (ChemCatChem 17/2015). ChemCatChem 2015. [DOI: 10.1002/cctc.201500910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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36
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Strong Metal-Support Interactions for Palladium Supported on TiO 2Catalysts in Heterogeneous Hydrogenation with Parahydrogen. ChemCatChem 2015. [DOI: 10.1002/cctc.201500790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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37
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Strong Metal-Support Interactions for Palladium Supported on TiO2Catalysts in the Heterogeneous Hydrogenation with Parahydrogen. ChemCatChem 2015. [DOI: 10.1002/cctc.201500618] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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38
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Development of new methods in modern selective organic synthesis: preparation of functionalized molecules with atomic precision. RUSSIAN CHEMICAL REVIEWS 2014. [DOI: 10.1070/rc2014v83n10abeh004471] [Citation(s) in RCA: 159] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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High-Resolution 3D Proton MRI of Hyperpolarized Gas Enabled by Parahydrogen and Rh/TiO 2Heterogeneous Catalyst. Chemistry 2014. [DOI: 10.1002/chem.201404052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Cover Picture: High-Resolution 3D Proton MRI of Hyperpolarized Gas Enabled by Parahydrogen and Rh/TiO 2Heterogeneous Catalyst (Chem. Eur. J. 37/2014). Chemistry 2014. [DOI: 10.1002/chem.201490154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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High-resolution 3D proton MRI of hyperpolarized gas enabled by parahydrogen and Rh/TiO2 heterogeneous catalyst. Chemistry 2014; 20:11636-9. [PMID: 24961814 DOI: 10.1002/chem.201403604] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Indexed: 11/11/2022]
Abstract
Several supported metal catalysts were synthesized, characterized, and tested in heterogeneous hydrogenation of propene with parahydrogen to maximize nuclear spin hyperpolarization of propane gas using parahydrogen induced polarization (PHIP). The Rh/TiO2 catalyst with a metal particle size of 1.6 nm was found to be the most active and effective in the pairwise hydrogen addition and robust, demonstrating reproducible results with multiple hydrogenation experiments and stability for ≥1.5 years. 3D (1) H magnetic resonance imaging (MRI) of 1 % hyperpolarized flowing gas with microscale spatial resolution (625×625×625 μm(3) ) and large imaging matrix (128×128×32) was demonstrated by using a preclinical 4.7 T scanner and 17.4 s imaging scan time.
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Evaluation of the Mechanism of Heterogeneous Hydrogenation of α,β-Unsaturated Carbonyl Compounds via Pairwise Hydrogen Addition. ACS Catal 2014. [DOI: 10.1021/cs500426a] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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45
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Development of new methods in modern selective organic synthesis: preparation of functionalized molecules with atomic precision. RUSSIAN CHEMICAL REVIEWS 2014. [DOI: 10.1070/rc2014v083n10abeh004471] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Parahydrogen-induced polarization (PHIP) in heterogeneous hydrogenation over bulk metals and metal oxides. Chem Commun (Camb) 2014; 50:875-8. [DOI: 10.1039/c3cc44939d] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Synthesis and characterisation of Co–Mo complexes containing the [Co(C2H8N2)3]2+ cation and [Mo2O7L]4− anion, where L is an oxalic, tartaric, citric or nitrilotriacetic acid residue. Polyhedron 2012. [DOI: 10.1016/j.poly.2012.08.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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High-active hydrotreating catalysts for heavy petroleum feeds: Intentional synthesis of CoMo sulfide particles with optimal localization on the support surface. Catal Today 2010. [DOI: 10.1016/j.cattod.2009.08.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Chapter 4 X‐Ray Photoelectron Spectroscopy for Investigation of Heterogeneous Catalytic Processes. ADVANCES IN CATALYSIS 2009. [DOI: 10.1016/s0360-0564(08)00004-7] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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