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Open accessJournal ArticleDOI: 10.1038/S41467-021-21604-7

Operando high-pressure investigation of size-controlled CuZn catalysts for the methanol synthesis reaction.

04 Mar 2021-Nature Communications (Nature Publishing Group)-Vol. 12, Iss: 1, pp 1435-1435
Abstract: Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu0.7Zn0.3 nanoparticles supported on ZnO/Al2O3, γ-Al2O3 and SiO2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al2O3 and CuZn/SiO2, but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO2. Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO2. In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity. The nature of the active species over Cu/ZnO catalysts for methanol synthesis remains elusive. Here, the authors shed light on the evolution of the nanoparticle/support interface and correlate its structural and chemical transformations with changes in the catalytic performance.

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Topics: Operando spectroscopy (61%), Catalysis (51%)

5 results found

Journal ArticleDOI: 10.1038/S41929-021-00625-X
Arik Beck1, Maxim Zabilskiy2, Mark A. Newton1, Olga V. Safonova2  +3 moreInstitutions (2)
01 Jun 2021-
Abstract: Copper-zinc-alumina catalysts are used industrially for methanol synthesis from feedstock containing carbon monoxide and carbon dioxide. The high performance of the catalyst stems from synergies that develop between its components. This important catalytic system has been investigated with a myriad of approaches, however, no comprehensive agreement on the fundamental source of its high activity has been reached. One potential source of disagreement is the considerable variation in pressure used in studies to understand a process that is performed industrially at pressures above 20 bar. Here, by systematically studying the catalyst state during temperature-programmed reduction and under carbon dioxide hydrogenation with in situ and operando X-ray absorption spectroscopy over four orders of magnitude in pressure, we show how the state and evolution of the catalyst is defined by its environment. The structure of the catalyst shows a strong pressure dependence, especially below 1 bar. As pressure gaps are a general problem in catalysis, these observations have wide-ranging ramifications. Copper-zinc-alumina is used in industry to catalyse the synthesis of methanol from CO2, but many aspects of its high performance remain elusive. Now, by using in situ and operando techniques over four orders of magnitude in pressure, the authors show how the catalyst structure and kinetics change with the applied conditions.

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Topics: Catalysis (56%), Carbon monoxide (53%), Heterogeneous catalysis (51%)

7 Citations

Open accessJournal ArticleDOI: 10.3390/CRYST11070824
15 Jul 2021-
Abstract: High order phenomena in the visible range and with polarization dependence in the ultraviolet (UV) region of the microphotoluminescence (micro-PL) spectrum in whispering-gallery mode (WGM) ZnO microrod cavity have been thoroughly studied at room temperature. WGM ZnO microrod cavity with good crystallinity is produced by the CVD growth method, and the ZnO microrod structures are characterized by structural and optical methods. Through the micro-PL spectrum measurement of the ZnO microrod, it is found that high-order resonance peaks appeared in the visible region. The different polarization conditions can be adjusted by rotating the angles of the polarizer, and it is proved that the micro-PL spectrum has strong polarization-dependent behavior in the UV region. Our results imply broad application potentials in the study of ZnO microrod-based photonic cavity devices.

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1 Citations

Open accessJournal ArticleDOI: 10.1002/CCTC.202100692
07 Oct 2021-Chemcatchem
Abstract: We report on an inverse model Cu/MgO methanol catalyst modified with 5 % zinc oxide at the Cu surface to element‐specifically probe the interplay of metallic copper and zinc oxide during reductive activation. The structure of copper and zinc was unraveled by in situ X‐ray diffraction (XRD) and in situ X‐ray absorption spectroscopy (XAS) supported by theoretical modelling of the extended X‐ray absorption fine structure and X‐ray absorption near‐edge structure spectra. Temperature‐programmed reduction in H2 during in situ XAS showed that copper was reduced starting at 145 °C. With increasing reduction temperature, zinc underwent first a geometrical change in its structure, followed by reduction. The reduced zinc species were identified as surface alloy sites, which coexisted from 200 °C to 340 °C with ZnO species at the copper surface. At 400 °C Zn−Cu bulk‐alloyed particles were formed. According to in situ XRD and in situ XAS, about half of the ZnO was not fully reduced, which can be explained by a lack of contact with copper. Our experimental results were further substantiated by density functional theory calculations, which verified that ZnO with neighboring Cu atoms reduced more easily. By combining these results, the distribution, phase and oxidation state of Zn species on Cu were estimated for the activated state of this model catalyst. This insight into the interplay of Cu and Zn forms the basis for deeper understanding the active sites during methanol synthesis.

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Topics: Catalysis (54%), Methanol (51%)

1 Citations

Open accessBook ChapterDOI: 10.1016/BS.ARCC.2021.09.001
Shenggang Li1, Yuchen Wang1, Bin Qin, Zhimin Zhou  +3 moreInstitutions (1)
01 Jan 2021-
Abstract: Computer-assisted rational design of heterogeneous catalysts has become a central theme of computational studies on industrial catalysis, which may contribute significantly to our impending transition from a fossil fuel-based energy and chemical industry into a renewable energy-based one. To this end, integrated research efforts in mechanistic elucidation of the relevant catalytic reactions remain essential, but emphasis must be further placed on the development of effective approaches in the rational design of industrial catalysts, where traditional methodologies must be combined with the new information-based technologies.

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Topics: Industrial catalysts (55%)

42 results found

Journal ArticleDOI: 10.1016/J.APSUSC.2010.10.051
Abstract: Chemical state X-ray photoelectron spectroscopic analysis of first row transition metals and their oxides and hydroxides is challenging due to the complexity of their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Our previous paper [M.C. Biesinger et al., Appl. Surf. Sci. 257 (2010) 887–898.] in which we examined Sc, Ti, V, Cu and Zn species, has shown that all the values of the spectral fitting parameters for each specific species, i.e. binding energy (eV), full wide at half maximum (FWHM) value (eV) for each pass energy, spin–orbit splitting values and asymmetric peak shape fitting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quantitative chemical state analysis. A more consistent, practical and effective approach to curve fitting was developed based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate literature databases and/or a compilation of literature references and (3) specific literature references where fitting procedures are available. This paper extends this approach to the chemical states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chemical states of these elements poses unique difficulties for chemical state analysis. The curve fitting procedures proposed use the same criteria as proposed previously but with the additional complexity of fitting of multiplet split spectra which has been done based on spectra of numerous reference materials and theoretical XPS modeling of these transition metal species. Binding energies, FWHM values, asymmetric peak shape fitting parameters, multiplet peak separation and peak area percentages are presented. The procedures developed can be utilized to remove uncertainties in the analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.

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Topics: Chemical state (54%), Curve fitting (52%), X-ray photoelectron spectroscopy (51%) ... show more

5,616 Citations

Open accessJournal ArticleDOI: 10.1126/SCIENCE.1219831
Malte Behrens1, Felix Studt2, Igor Kasatkin3, Stefanie Kühl3  +11 moreInstitutions (5)
18 May 2012-Science
Abstract: Unlike homogeneous catalysts, heterogeneous catalysts that have been optimized through decades are typically so complex and hard to characterize that the nature of the catalytically active site is not known. This is one of the main stumbling blocks in developing rational catalyst design strategies in heterogeneous catalysis. We show here how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al{sub 2}O{sub 3} methanol synthesis catalyst. Using a combination of experimental evidence from bulk-, surface-sensitive and imaging methods collected on real high-performance catalytic systems in combination with DFT calculations. We show that the active site consists of Cu steps peppered with Zn atoms, all stabilized by a series of well defined bulk defects and surface species that need jointly to be present for the system to work.

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1,541 Citations

Journal ArticleDOI: 10.1126/SCIENCE.1069325
15 Mar 2002-Science
Abstract: In situ transmission electron microscopy is used to obtain atom-resolved images of copper nanocrystals on different supports. These are catalysts for methanol synthesis and hydrocarbon conversion processes for fuel cells. The nanocrystals undergo dynamic reversible shape changes in response to changes in the gaseous environment. For zinc oxide-supported samples, the changes are caused both by adsorbate-induced changes in surface energies and by changes in the interfacial energy. For copper nanocrystals supported on silica, the support has negligible influence on the structure. Nanoparticle dynamics must be included in the description of catalytic and other properties of nanomaterials. In situ microscopy offers possibilities for obtaining the relevant atomic-scale insight.

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Topics: Nanomaterials (53%), Nanoparticle (52%), Copper (51%)

1,004 Citations

Open accessJournal ArticleDOI: 10.1126/SCIENCE.AAL3573
24 Mar 2017-Science
Abstract: The active sites over commercial copper/zinc oxide/aluminum oxide (Cu/ZnO/Al2O3) catalysts for carbon dioxide (CO2) hydrogenation to methanol, the Zn-Cu bimetallic sites or ZnO-Cu interfacial sites, have recently been the subject of intense debate. We report a direct comparison between the activity of ZnCu and ZnO/Cu model catalysts for methanol synthesis. By combining x-ray photoemission spectroscopy, density functional theory, and kinetic Monte Carlo simulations, we can identify and characterize the reactivity of each catalyst. Both experimental and theoretical results agree that ZnCu undergoes surface oxidation under the reaction conditions so that surface Zn transforms into ZnO and allows ZnCu to reach the activity of ZnO/Cu with the same Zn coverage. Our results highlight a synergy of Cu and ZnO at the interface that facilitates methanol synthesis via formate intermediates.

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Topics: Catalysis (53%), Methanol (51%)

687 Citations

Journal ArticleDOI: 10.1006/JCAT.2000.2930
Abstract: Dynamic changes in the structure and catalytic activity of Cu/ZnO methanol synthesis catalysts have been investigated by a further developed in situ method, which combines X-ray diffraction (XRD), X-ray absorption fine structure spectroscopy (XAFS), and on-line catalytic measurements by mass spectrometry. The temperature-programmed reduction of copper was monitored both by in situ quick-EXAFS (QEXAFS) and on-line mass spectrometry. The results indicate that under typical mild reduction conditions very small copper particles (10–15 A) are formed. Upon change in the reduction potential of the methanol synthesis gas, reversible changes of the Cu–Cu coordination number are observed by EXAFS. These structural changes are accompanied by changes in the catalytic activity and the highest activities were observed after exposure to the most reducing conditions. In this state the catalyst exhibited low Cu–Cu coordination numbers. These results support the model that reversible changes in the wetting of ZnO by Cu may occur upon changes in the reaction conditions. The results also show that such dynamical changes in Cu morphology may influence the catalytic properties. All the conditions used in the above studies are less severe than those observed to result in bulk alloy formation. However, additional XAFS measurements at higher temperatures have been performed and EXAFS spectra have been simulated to address the possibility for Cu–Zn alloy formation as suggested by recent results in literature. Only under severe reduction conditions was significant alloying of copper and zinc observed in EXAFS in addition to the morphological changes. Such changes have not been seen in the Cu/SiO2 system.

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Topics: X-ray absorption fine structure (54%), Copper (51%)

474 Citations

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