Suchergebnisse

Resumen del trabajo presentado al Microscopy at the Frontiers of Science Congress Series (MFS), celebrado en el Parque de las Ciencias de Granada (España) del 11 al 13 de septiembre de 2019. ; Research supported by the Spanish MINECO (MAT2016-79776-P, AEI/FEDER, EU), Government of Aragon through project DGA E13_17R (FEDER, EU), European Union H2020 programs "ESTEEM3" (823717), Flag-ERA GATES (JTC 2017), French Agence Nationale de la Recherche (ANR-11-LABX-0058-NIE) and SOLEIL synchrotron / Laboratoire Léon Brilluoin fellowship. ; Peer reviewed

In this work, we will report the generation of Au clusters in a purely siliceous MCM-22 zeolite. The catalytic properties of these Au clusters have been tested for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA-oil). The Au clusters encapsulated in the MCM-22 zeolite are highly active and selective for the oxidation of cyclohexane to KA-oil, which is superior to Au nanoparticles on the same support. These results suggest that Au clusters are highly active for the activation of oxygen to produce radical species. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the ''Severo Ochoa Program'' (SEV-2016-0683). R. A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE). ; Peer reviewed

Resumen del trabajo presentado al Microscopy at the Frontiers of Science Congress Series (MFS), celebrado en el Parque de las Ciencias de Granada (España) del 11 al 13 de septiembre de 2019. ; Research supported by the Spanish MINECO (MAT2016-79776-P, AEI/FEDER, EU), Government of Aragon through project DGA E13_17R (FEDER, EU) and European Union H2020 programs "ESTEEM3" (823717) and Flag-ERA GATES (JTC 2017). ; Peer reviewed

[EN] In this work, we will report the generation of Au clusters in a purely siliceous MCM-22 zeolite. The catalytic properties of these Au clusters have been tested for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA-oil). The Au clusters encapsulated in the MCM-22 zeolite are highly active and selective for the oxidation of cyclohexane to KA-oil, which is superior to Au nanoparticles on the same support. These results suggest that Au clusters are highly active for the activation of oxygen to produce radical species. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683). The authors also thank the Microscopy Service of UPV for kind help with TEM and STEM measurements. Mr J. A. Gaona is greatly acknowledged for his very helpful assistance on the catalytic studies. The XAS data were acquired at European Synchrotron Radiation Facility. The HAADF-HRSTEM studies were conducted in the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA)-Universidad de Zaragoza (Spain), Spanish ICTS National facility. R. A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE). ; Liu, L.; Arenal, R.; Meira, DM.; Corma Canós, A. (2019). Generation of gold nanoclusters encapsulated in an MCM-22 zeolite for the aerobic oxidation of cyclohexane. Chemical Communications. 55(11):1607-1610. https://doi.org/10.1039/c8cc07185c ; S ; 1607 ; 1610 ; 55 ; 11 ; Claus, P. (2005). Heterogeneously catalysed hydrogenation using gold catalysts. Applied Catalysis A: General, 291(1-2), 222-229. doi:10.1016/j.apcata.2004.12.048 ; Hashmi, A. S. K., & Hutchings, G. J. (2006). Gold Catalysis. Angewandte Chemie International Edition, 45(47), 7896-7936. doi:10.1002/anie.200602454 ; Liu, L., & Corma, A. (2018). Metal Catalysts for ...

1607 1610 55 11 ; S ; [EN] In this work, we will report the generation of Au clusters in a purely siliceous MCM-22 zeolite. The catalytic properties of these Au clusters have been tested for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA-oil). The Au clusters encapsulated in the MCM-22 zeolite are highly active and selective for the oxidation of cyclohexane to KA-oil, which is superior to Au nanoparticles on the same support. These results suggest that Au clusters are highly active for the activation of oxygen to produce radical species. This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683). The authors also thank the Microscopy Service of UPV for kind help with TEM and STEM measurements. Mr J. A. Gaona is greatly acknowledged for his very helpful assistance on the catalytic studies. The XAS data were acquired at European Synchrotron Radiation Facility. The HAADF-HRSTEM studies were conducted in the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA)-Universidad de Zaragoza (Spain), Spanish ICTS National facility. R. A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE). Liu, L.; Arenal, R.; Meira, DM.; Corma Canós, A. (2019). Generation of gold nanoclusters encapsulated in an MCM-22 zeolite for the aerobic oxidation of cyclohexane. Chemical Communications. 55(11):1607-1610. https://doi.org/10.1039/c8cc07185c Claus, P. (2005). Heterogeneously catalysed hydrogenation using gold catalysts. Applied Catalysis A: General, 291(1-2), 222-229. doi:10.1016/j.apcata.2004.12.048 Hashmi, A. S. K., & Hutchings, G. J. (2006). Gold Catalysis. Angewandte Chemie International Edition, 45(47), 7896-7936. doi:10.1002/anie.200602454 Liu, L., & Corma, A. (2018). Metal Catalysts for Heterogeneous ...

This article belongs to the Special Issue Characterization of Disorder in Carbons. ; Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp2 and sp3 carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm−1) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm−1 and compared to the height of the G band, depends on the sp2 content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm−1 and the G band at ≈1500–1600 cm−1 when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D3, D4 and D5 bands, which is not the case for a-C:H samples. ; R.A. gratefully acknowledges the support from the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P) and from the European Union H2020 program "ESTEEM3" (823717).". ; Peer reviewed

The catalytic subnanometric metal clusters with a few atoms can be regarded as an intermediate state between single atoms and metal nanoparticles (>1 nm). Their molecule-like electronic structures and flexible geometric structures bring rich chemistry and also a different catalytic behavior, in comparison with the single-atom or nanoparticulate counterparts. In this work, by combination of operando IR spectroscopy techniques and electronic structure calculations, we will show a comparative study on Pt catalysts for CO + NO reaction at a very low temperature range (140–200 K). It has been found that single Pt atoms immobilized on MCM-22 zeolite are not stable under reaction conditions and agglomerate into Pt nanoclusters and particles, which are the working active sites for CO + NO reaction. In the case of the catalyst containing Pt nanoparticles (∼2 nm), the oxidation of CO to CO2 occurs in a much lower extension, and Pt nanoparticles become poisoned under reaction conditions because of a strong interaction with CO and NO. Therefore, only subnanometric Pt clusters allow NO dissociation at a low temperature and CO oxidation to occur well on the surface, while CO interaction is weak enough to avoid catalyst poisoning, resulting in a good balance to achieve enhanced catalytic performance. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683) and MAT2017-82288-C2-1-P projects. L.L. thanks ITQ for providing a contract. E.F. thanks MINECO for her fellowship SVP-2013-068146. The authors also thank Microscopy Service of UPV for the TEM and STEM measurements. The HRSTEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. R.A. acknowledges support from Spanish MINECO grant MAT2016-79776-P (AEI/FEDER, UE), from the Government of Aragon and the European Social Fund (grant number E13_17R, FEDER, UE), and from the European Union H2020 program "ESTEEM3" (grant number 823717). ; Peer reviewed

Understanding the behavior and dynamic structural transformation of subnanometric metal species under reaction conditions will be helpful for understanding catalytic phenomena and for developing more efficient and stable catalysts based on single atoms and clusters. In this work, the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite has been studied by in situ transmission electron microscopy (TEM). By correlating the results from in situ TEM studies and the results obtained in a continuous fix-bed reactor, it has been possible to delimitate the factors that control the dynamic agglomeration and redispersion behavior of metal species under reaction conditions. The dynamic reversible transformation between atomically dispersed Pt species and clusters/nanoparticles during CO oxidation at different temperatures has been elucidated. It has also been confirmed that subnanometric Pt clusters can be stabilized in MCM-22 crystallites during NO reduction with CO and H. ; This work has been supported by the European Union through the European ResearchCouncil (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish governmentthrough the"Severo Ochoa Program"(SEV-2016-0683). L.L. thanks ITQ for providing acontract. We also thank Microscopy Service of UPV for the TEM and STEM mea-surements. The in situ TEM experiments were performed in the Center for FunctionalNanomaterials, which is a US DOE Office of Science User Facility, at BrookhavenNational Laboratory under contract number DESC0012704. The HAADF-HRSTEMstudies have been conducted in the Laboratorio de Microscopias Avanzadas (LMA) at theInstituto de Nanociencia de Aragon (INA)-Universidad de Zaragoza (Spain), SpanishICTS National facility. R.A. gratefully acknowledges the support from the SpanishMinistry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE).

Molybdenum disulfide nanosheets covalently modified with porphyrin were prepared and fully characterized. Neither the porphyrin absorption nor its fluorescence was notably affected by covalent linkage to MoS2. The use of transient absorption spectroscopy showed that a complex ping‐pong energy‐transfer mechanism, namely from the porphyrin to MoS2 and back to the porphyrin, operated. This study reveals the potential of transition‐metal dichalcogenides in photosensitization processes. ; This project has received funding from EC H2020 under the Marie Sklodowska‐Curie grant agreement No. 642742. HRSTEM and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016‐79776‐P (AEI/FEDER, UE) and from EC H2020 programs "Graphene Flagship" (785219), FLAG‐ERA—"GATES" (JTC‐PCI2018‐093137) and "ESTEEM3" (823717). R.A. also acknowledges Government of Aragon under the project "Construyendo Europa desde Aragon" 2014‐2020 (grant number E13_17R). ; Peer reviewed

This article belongs to the Section Nanocomposite Materials. ; Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical properties of TMD/pyrene are assessed via electronic absorption and fluorescence emission spectroscopy. High-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy confirms extensive pyrene surface coverage, with density functional theory calculations suggesting a strongly bound stable parallel-stacked pyrene coverage of ~2–3 layers on the TMD surfaces. Raman spectroscopy of exfoliated TMDs while irradiating at 0.9 mW/4 μm2 under ambient conditions shows new and strong Raman bands due to oxidized states of Mo and W. Yet remarkably, under the same exposure conditions TMD/pyrene remain unperturbed. The current findings demonstrate that pyrene physisorbed on MoS2 and WS2 acts as an environmental barrier, preventing oxidative surface reactions in the TMDs catalyzed by moisture, air, and assisted by laser irradiation. Raman spectroscopy confirms that the hybrid materials stored under ambient conditions for two years remained structurally unaltered, corroborating the beneficial role of pyrene for not only hindering oxidation but also inhibiting aging. ; This research was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742, under the "Graphene Flagship" project grant agreement No 785219 and under the ESTEEM-3 project grant agreement No 823717. This research was also partially funded by the project "Advanced Materials and Devices" (MIS 5002409), which is implemented under the "Action for the Strategic Development on the Research and Technological Sector" funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). This work was supported by the COST Action CA15107 MultiComp. This research was also supported by the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P), from the Government of Aragon and the European Social Fund under the project "Construyendo Europa desde Aragon" 2014–2020 (grant number E13_17R). ; Peer reviewed

[EN] The catalytic subnanometric metal clusters with a few atoms can be regarded as an intermediate state between single atoms and metal nanoparticles (>1 nm). Their molecule-like electronic structures and flexible geometric structures bring rich chemistry and also a different catalytic behavior, in comparison with the single-atom or nanoparticulate counterparts. In this work, by combination of operando IR spectroscopy techniques and electronic structure calculations, we will show a comparative study on Pt catalysts for CO + NO reaction at a very low temperature range (140-200 K). It has been found that single Pt atoms immobilized on MCM-22 zeolite are not stable under reaction conditions and agglomerate into Pt nanoclusters and particles, which are the working active sites for CO + NO reaction. In the case of the catalyst containing Pt nanoparticles (similar to 2 nm), the oxidation of CO to CO2 occurs in a much lower extension, and Pt nanoparticles become poisoned under reaction conditions because of a strong interaction with CO and NO. Therefore, only subnanometric Pt clusters allow NO dissociation at a low temperature and CO oxidation to occur well on the surface, while CO interaction is weak enough to avoid catalyst poisoning, resulting in a good balance to achieve enhanced catalytic performance. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014671093, SynCatMatch) and the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683) and MAT2017-82288-C2-1-P projects. L.L. thanks ITQ for providing a contract. E.F. thanks MINECO for her fellowship SVP-2013-068146. The authors also thank Microscopy Service of UPV for the TEM and STEM measurements. The HRSTEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. RA. acknowledges support from Spanish MINECO grant MAT2016-79776-P (AEI/FEDER, UE), from the Government of Aragon and the European Social Fund (grant number E13_17R, FEDER, UE), and ...

[EN] Identification of active sites in heterogeneous metal catalysts is critical for understanding the reaction mechanism at the molecular level and for designing more efficient catalysts. Because of their structural flexibility, subnanometric metal catalysts, including single atoms and clusters with a few atoms, can exhibit dynamic structural evolution when interacting with substrate molecules, making it difficult to determine the catalytically active sites. In this work, Pt catalysts containing selected types of Pt entities (from single atoms to clusters and nanoparticles) have been prepared, and their evolution has been followed, while they were reacting in a variety of heterogeneous catalytic reactions, including selective hydrogenation reactions, CO oxidation, dehydrogenation of propane, and photocatalytic H-2 evolution reaction. By in situ X-ray absorption spectroscopy, in situ IR spectroscopy, and high-resolution electron microscopy techniques, we will show that some characterization techniques carried out in an inadequate way can introduce confusion on the interpretation of coordination environment of highly dispersed Pt species. Finally, the combination of catalytic reactivity and in situ characterization techniques shows that, depending on the catalyst-reactant interaction and metal-support interaction, singly dispersed metal atoms can rapidly evolve into metal clusters or nanoparticles, being the working active sites for those abovementioned heterogeneous reactions. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683). L.L. thanks ITQ for providing a contract. The authors also thank Microscopy Service of UPV for the TEM and STEM measurements. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was ...

[EN] Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 degrees C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene. ; This work was funded by the Spanish Government (Consolider Ingenio 2010-MULTICAT (CSD2009-00050) and MAT2014-52085-C2-1-P) and by the Generalitat Valenciana (Prometeo). The Severo Ochoa Program (SEV-2012-0267) is gratefully acknowledged. L.L. thanks ITQ for a contract. The authors also thank the Microscopy Service of UPV for the TEM and STEM measurements. The HAADF-HRSTEM works were conducted in the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA)-Universidad de Zaragoza (Spain), a Spanish ICTS National Facility. Some of the research leading to these results has received funding from the European Union Seventh Framework Program under Grant Agreement 312483-ESTEEM2 (Integrated Infrastructure Initiative-I3). R.A. also acknowledges funding from the Spanish Ministerio de Economia y Competitividad (FIS2013-46159-C3-3-P) and the European Union Horizon 2020 research and innovation programme under the Marie Sldodowska-Curie grant agreement No. 642742. ; Liu, L.; Díaz ...

Realizing the full potential of oxide‐supported single‐atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one‐pot combination of Ru1/CeO2 and Rh1/CeO2 SACs enables a highly selective olefin isomerization‐hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double‐bond migration and anti‐Markovnikov α‐olefin hydrosilylation, respectively. First‐principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single‐pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio‐selectivity (>95 %) even from industrially‐relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide‐supported single‐atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes. ; R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016‐79776‐P (AEI/FEDER, UE) and from the European Union H2020 programs "ESTEEM3" (823717). The authors acknowledge support by the state of Baden‐Württemberg through bwHPC (bwUnicluster and JUSTUS, RV bw17D01), by the GRK 2450 and by the Helmholtz Association. This research received funding from the Max Planck Society, and the Fonds der Chemische Industrie of Germany. Funding from the Spanish Ministry of Science, Innovation and Universities (Severo Ochoa program SEV‐2016‐0683 and grant RTI2018‐096399‐A‐I00) is also acknowledged. B.B.S. acknowledges the Alexander von Humboldt Foundation for a postdoctoral scholarship. Open Access funding is provided by the Max Planck Society. ; Peer reviewed

Realizing the full potential of oxide¿supported single¿atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one¿pot combination of Ru1/CeO2 and Rh1/CeO2 SACs enables a highly selective olefin isomerization¿hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double¿bond migration and anti¿Markovnikov ¿¿olefin hydrosilylation, respectively. First¿principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single¿pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio¿selectivity (>95¿%) even from industrially¿relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide¿supported single¿atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes. ; X‐ray absorption experiments were performed at the ALBA Synchrotron Light Source (Spain), experiments 2018082961 and 2019023278. L. Simonelli and C. Marini (CLAESS‐ALBA beamline) are thanked for beamline setup. E. Andrés, M. E. Martínez, M. García, and I. López (ITQ), are acknowledged for their assistance with XAS experiments. J. Büscher, J. Ternedien, B. Spliethoff, and C. Wirtz (MPI‐KOFO) are acknowledged for the performance of XPS, XRD, BF‐TEM and 2H NMR experiments, respectively. I. C. de Freitas (MPI‐KOFO) is thanked for assistance with Raman spectroscopy. J. M. Salas (ITQ) is gratefully acknowledged for his contribution to CO‐FTIR experiments. J. J. Barnes and Shell (Amsterdam) are acknowledged for kindly providing an industrial olefin mixture as feed. Authors are thankful to F. Schüth for the provision of lab space and continued support. Part of the HRSTEM and EDX‐STEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016‐79776‐P (AEI/FEDER, UE) and from the European Union H2020 programs "ESTEEM3" (823717). The authors acknowledge support by the state of Baden‐Württemberg through bwHPC (bwUnicluster and JUSTUS, RV bw17D01), by the GRK 2450 and by the Helmholtz Association. This research received funding from the Max Planck Society, and the Fonds der Chemische Industrie of Germany. Funding from the Spanish Ministry of Science, Innovation and Universities (Severo Ochoa program SEV‐2016‐0683 and grant RTI2018‐096399‐A‐I00) is also acknowledged. B.B.S. acknowledges the Alexander von Humboldt Foundation for a postdoctoral scholarship. Open Access funding is provided by the Max Planck Society.