Suchergebnisse

[EN] Aromatic azoxy compounds have wide applications and they can be prepared by stoichiometric or catalytic reactions with H2O2 or N2H4 starting from anilines or nitroarenes. In this work, we will present the direct chemoselective hydrogenation of nitroarenes with H-2 to give aromatic azoxy compounds under base-free mild conditions, with a bifunctional catalytic system formed by Ni nanoparticles covered by a few layers of carbon (Ni@C NPs) and CeO2 nanoparticles. The catalytic performance of Ni@C-CeO2 catalyst surpasses the state-of-art Au/CeO2 catalyst for the direct production of azoxybenzene from nitrobenzene. By means of kinetic and spectroscopic results, a bifunctional mechanism is proposed in which, the hydrogenation of nitrobenzene can be stopped at the formation of azoxybenzene with >95% conversion and >93% selectivity, or can be further driven to the formation of azobenzene with >85% selectivity. By making a bifunctional catalyst with a non-noble metal, one can achieve chemoselective hydrogenation of nitroarenes not only to anilines, but also to corresponding azoxy and azo compounds. (C) 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ; This work has been supported by the European Union through the SynCatMatch project (ERC-AdG-2014-671093). Financial supports by the Spanish Government-MINECO through the program "Severo Ochoa" (SEV-2016-0683) are gratefully acknowledged. The authors also thank the Microscopy Service of UPV for kind help with TEM and STEM measurements. ; Liu, L.; Concepción Heydorn, P.; Corma Canós, A. (2019). Modulating the catalytic behavior of non-noble metal nanoparticles by inter-particle interaction for chemoselective hydrogenation of nitroarenes into corresponding azoxy or azo compounds. Journal of Catalysis. 369:312-323. https://doi.org/10.1016/j.jcat.2018.11.011 ; S ; 312 ; 323 ; 369

Metallic cobalt nanoparticles with surface CoOx patches covered by thin layered carbon (named Co@C) have been directly synthesized by thermal decomposition of Co-EDTA complex. Raman spectra and HRTEM images suggest that discontinuities can be found in the disordered layered carbon. XPS shows that the CoOx patches in the Co@C nanoparticles can reduced to metallic Co by H-2 under reaction conditions (7 bar at 120 degrees C), and H-2-D-2 exchange experiments show that the reduced metallic Co nanoparticles covered by carbon layers can dissociate H-2. The Co@C nanoparticles show excellent activity and selectivity during chemoselective hydrogenation of nitroarenes for a wide scope of substrates under mild reaction conditions. Based on the results from DRIFTS adsorption experiments, we propose that metallic Co in the Co@C nanoparticles is the active phase. The role of the carbon layers is to protect the Co from overoxidation by air, leading to the chemoselective hydrogenation of nitroarenes. (C) 2016 Elsevier Inc. All rights reserved. ; L.L. thanks ITQ for a contract. The European Union is also acknowledged by ERC-AdG-2014-671093-SynCatMatch. The authors also thank the Microscopy Service of UVP for kind help with TEM and STEM measurements. ; Liu, L.; Concepción Heydorn, P.; Corma Canós, A. (2016). Non-noble metal catalysts for hydrogenation: A facile method for preparing Co nanoparticles covered with thin layered carbon. Journal of Catalysis. 340:1-9. doi:10.1016/j.jcat.2016.04.006 ; S ; 1 ; 9 ; 340

[EN] The selective dehydration of glycerol to hydroxyacetone (acetol) was studied with Cu-based mixed oxides derived from hydrotalcite as catalysts in a continuous flow fix-bed reactor. Catalysts were prepared by co-precipitation and characterized by ICP, N-2 adsorption, XRD, NH3-TPD, CO2-TPD, TPR and TEM. Different parameters were investigated to develop the most appropriate material as well as to determine the function of every metallic species. The optimized Cu-Mg-AlOx offered approximate to 60% acetol selectivity at >90% glycerol conversion (approximate to 80% liquid yield, up to TOS = 9 h). The catalyst could be regenerated by calcination, achieving full activity recovery after five re-cycles. "In-situ" FTIR and XPS measurements evidenced that the presence of Cu, specially the most active Cu1+ species, was essential to carry out the dehydration to acetol with high reaction rates, and to form the preferred intermediate (with C=O group); although a minor contribution from Cu-0 and Cu2+ species could not be discarded. ; Financial support by Spanish Government (CTQ-2015-67592, PGC2018-097277-B-100 and SEV-2016-0683) and PhosAgro/UNESCO/IUPAC Partnership (Proj. 139) is gratefully acknowledged. J.M. also thanks Spanish Government (CTQ-2015-67592) for his FPI fellowship. ; Mazarío-Santa-Pau, J.; Concepción Heydorn, P.; Ventura, M.; Domine, ME. (2020). Continuous catalytic process for the selective dehydration of glycerol over Cu-based mixed oxide. Journal of Catalysis. 385:160-175. https://doi.org/10.1016/j.jcat.2020.03.010 ; S ; 160 ; 175 ; 385 ; BP Statistical Review of World Energy, #BPstats. 40 (2015). bp.com/statisticalreview. ; Stöcker, M. (2008). Biofuels and Biomass‐To‐Liquid Fuels in the Biorefinery: Catalytic Conversion of Lignocellulosic Biomass using Porous Materials. Angewandte Chemie International Edition, 47(48), 9200-9211. doi:10.1002/anie.200801476 ; Huber, G. W., Iborra, S., & Corma, A. (2006). Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering. Chemical ...

[EN] We show a facile method to prepare surface-clean monodispersed small and stable CuOx nanoparticles with controllable average sizes from below 1 nm up to similar to 5 nm without using bulk capping agent. Structural and surface characterizations show that the chemical states of CuOx nanoparticles and their interactions with O-2 are dependent on the particle size. To show their relevance to catalysis, the well-defined monodispersed CuOx nanoparticles have been used for oxidative coupling of alkynes. While the generally used CuCl catalysts presents a reaction induction period and agglomerate into CuOx nanoparticles during the reaction, the induction period disappears when monodispersed CuOx nanoparticles (similar to 2 nm) were used as catalyst. Supported CuOx nanoparticles on TiO2 behave in the same way as monodispersed CuOx nanoparticles. Kinetic, spectroscopic, and isotopic studies show that O-2 activation is the rate-controlling step and that the nature of the oxygen species formed on supported CuOx nanoparticles is dependent on the size of CuOx and determine the catalytic properties for oxidative coupling of alkynes. ; L.L. thanks ITQ for providing a contract. The authors also thank the Microscopy Service of UPV for kind help on TEM and STEM measurements. Financial supports from Consolider-Ingenio 2010 (project MULTICAT) and "Severo Ochoa" program are also gratefully acknowledged. The European Union is also acknowledged by ERC-AdG-2014-671093 - SynCatMatch. ; Liu, L.; Matsushita, T.; Concepción Heydorn, P.; Leyva Perez, A.; Corma Canós, A. (2016). Facile Synthesis of Surface-Clean Monodispersed CuOx Nanoparticles and Their Catalytic Properties for Oxidative Coupling of Alkynes. ACS Catalysis. 6(4):2211-2221. https://doi.org/10.1021/acscatal.5b02935 ; S ; 2211 ; 2221 ; 6 ; 4

[EN] Combining IR spectroscopy of NO adsorption on copper exchanged molecular sieves with the chabazite structure, i.e. Cu-SAPO-34 and Cu-SSZ-13, and theoretical calculations, different types of copper species have been identified. On one hand, [Cu¿OH]+ species can be accurately distinguished, characterized by a ¿NO frequency at 1788¿ 1798 cm¿1 depending on their location in the chabazite structure (6R vs. 8R) and composition (Cu-SAPO-34 vs. Cu-SSZ-13). On the other hand, dimeric copper oxo [Cu¿O¿ Cu]2+ species have been properly identified by means of DFT modelling, that proposes a ¿NO stretching frequency of 1887 cm¿1, which has been confirmed experimentally in the Cu-SAPO-34 sample. Finally the location of isolated Cu2+ ions either in the 6R units or in the 8R positions of the chabazite cavity could be accurately defined according to DFT data, and validated in the experimental IR spectra with IR bands between 1907 and 1950 cm¿1. Regarding to Cu+ species, IR spectroscopy of CO reveals different types of Cu+ species as evidenced by their ability to form mono, di and try carbonyls. The unambiguous differentiation of different types of copper species is of great interest in further identification of active sites for the NH3- SCR reaction. ; This work has been supported by the Spanish Government through "Severo Ochoa Program" (SEV 2012-0267), and MAT2015-71261-R, the European Union through ERC-AdG-2014-671093 (SynCatMatch); and the Generalitat Valenciana through the Prometeo program (PROMETEOII/2013/011). R.M. acknowledges "La Caixa - Severo Ochoa" International PhD Fellowships (call 2015). ; Concepción Heydorn, P.; Boronat Zaragoza, M.; Millan, R.; Moliner Marin, M.; Corma Canós, A. (2017). Identification of Distinct Copper Species in Cu-CHA Samples Using NO as Probe Molecule. A Combined IR Spectroscopic and DFT Study. Topics in Catalysis. 60(19-20):1653-1663. https://doi.org/10.1007/s11244-017-0844-7 ; S ; 1653 ; 1663 ; 60 ; 19-20 ; Wilken N, Wijayanti K, Kamasamudram K, Currier NW, Vedaiyan R, Yezerets A, ...

[EN] In this work, we have studied the catalytic activity of different silicates (MFI, MCM-41, and Beta) containing Lewis acid sites (including Sn, Ti, Zr, and Hf) for the tandem N-alkylation reaction of aniline with benzyl alcohol. The Hf- and Zr-Beta were the most active catalysts for this transformation, showing in both cases selectivities toward the corresponding N-benzylaniline higher than 97%. FTIR and DFT analyses confirm that the active sites in the Hf-Beta catalyst for this process are the open sites where one of the four Hf-O bonds is hydrolyzed. Moreover, the amount of these active species could be notoriously increased with previous thermal treatment of the Lewis acid zeolite with benzyl alcohol. Isotopically labeled experiments and theoretical mechanistic studies reveal that the N-alkylation reaction occurs through a hydrogen borrowing pathway, in which in situ Hf-hydride species were generated. Finally, the Hf-Beta zeolite was reused several times in the N-alkylation reaction without any appreciable deactivation detected. This catalytic system could be expanded to a variety of amines, including aliphatic and biomass-derived amines. ; This work has been supported by the Spanish Government through "severo Ochoa" (SEV-2016-0683, MINECO), MAT2017-82288-C2-1-P (AEI/FEDER, UE), and RTI2018101033-B-I00 (MCIU/AEI/FEDER, UE). Dr. Susana Valencia is acknowledged for the preparation of the Ti-Beta sample. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. Part of the computations were performed on the Tirant III cluster of the Servei d'Informa`tica of the University of Valencia. ; Rojas-Buzo, S.; Concepción Heydorn, P.; Corma Canós, A.; Moliner Marin, M.; Boronat Zaragoza, M. (2021). In-Situ-Generated Active Hf-hydride in Zeolites for the Tandem N-Alkylation of Amines with Benzyl Alcohol. ACS Catalysis. 11(13):8049-8061. https://doi.org/10.1021/acscatal.1c01739 ; S ; 8049 ; 8061 ; 11 ; 13

[EN] An efficient process for synthesizing a high added-value N-heterocycle (2-methylpiperazine, 2-MP) via reductive amination of hydroxyacetone or acetol (product of the selective dehydration of glycerol) with ethylenediamine by using Pd supported catalysts under mild reaction conditions is here presented. Catalysts based on Pd nanoparticles supported on metallic oxides and mixed oxides were prepared and characterized by ICP analysis, XRD, HR-TEM, and NH3-TPD, among others. Catalytic activity comparisons of Pd-based materials (also including commercial references) were done and obtained results correlated with metal particle morphology (analyzed by CO-FTIR) and its ability to activate the C = N bond. The best results were attained with Pd/TiO2-Al2O3 and Pd/ZrO2-Al2O3, the former yielding >80% of 2-MP. The Pd/TiO2-Al2O3 catalyst successfully enables the activation of the imine group (C = N), due to a larger number of unsaturated Pd sites in its nanoparticles, while keeping a suitable acidity to effectively and selectively carry out the reductive cyclo-amination reaction even with lower catalyst loadings. This research work offers a new and sustainable catalytic route for the synthesis of organo-nitrogen compounds taking advantage of renewable raw materials (i.e. acetol) as a carbon source and using efficient Pd supported catalysts. ; The authors express their gratitude to the Spanish Government for the funding (MICINN: CTQ2015-67592, PGC2018-097277-B-I00 and Severo Ochoa Program: SEV-2016-0683). J. M. thanks the MICINN (CTQ2015-67592) for his PhD scholarship. Z. R. thanks the Islamic Center Association for Guidance and Higher Education for his PhD scholarship. The authors also thank the Electron Microscopy Service of Universitat Politecnica de Valencia for their support and M. Parreno-Romero for her assistance with the measurements. ; Mazarío-Santa-Pau, J.; Raad, Z.; Concepción Heydorn, P.; Cerdá-Moreno, C.; Domine, ME. (2020). Pd supported on mixed metal oxide as an efficient catalyst for the reductive ...

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acscatal.8b04717." ; [EN] Despite the intense investigation on the NH3-SCR-NOx reaction mechanism catalyzed by small pore Cu-CHA zeolites, neither the rate-determining step of the process nor the exact nature of the active sites under reaction conditions are clearly established. In this work, in situ EPR and IR techniques combined with DFT calculations are applied to the study of the oxidation half-cycle of the NH3-SCR-NOx reaction on Cu-SSZ-13 and Cu-SAPO-34 catalysts. EPR and IR spectroscopies unambiguously show that Cu+ is oxidized to Cu2+ at room temperature in the presence of the reaction mixture (NO, O-2, and NH3) or NO and O-2, producing adsorbed NO2, nitrites, and nitrates. Several pathways are proposed from DFT calculations to oxidize Cu+ cations placed in the plane of the 6R ring units of SSZ-13 and SAPO-34 to Cu2+, either by NO2 alone or by a mixture of NO and O-2, with activation energy barriers lower than 70 kJ mol(-1). The results reported here demonstrate that a reaction mechanism invoking the formation of nitrate/nitrite intermediates on copper cations attached to the zeolite framework can be operational in the low-temperature region (T 350 degrees C). Moreover, different intermediates, nitrites versus nitrates, are preferentially stabilized, depending on the catalyst composition, silicoaluminophosphate vs aluminosilicate. ; This work was supported by the Spanish Government through "Severo Ochoa Program" (Nos. SEV 2012-0267; SEV-2016-0683), No. MAT2015-71261-R, and No. CTQ2015-68951-C3-1-R, and by the European Union through No. ERC-AdG-2014-671093 (SynCatMatch). Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational resources and ...

[EN] By a combination of theoretical modeling and XPS and SERS spectroscopic studies, it has been found that it is possible to stabilize metallic copper species under oxidizing reaction conditions by adjusting the atomicity of subnanometer copper clusters. Small Cu-5 clusters display low reactivity toward O-2 dissociation, being less susceptible to oxidation than larger Cu-8 or Cu-20 systems. However, in the presence of water this reactivity is strongly enhanced, leading to oxidized Cu-5 clusters. In that case, the interaction of Cu-5 with atomic O oxygen is weak, favoring recombination and O-2 desorption, suggesting an easier transfer of O atoms to other reactant molecules. In contrast, copper clusters of higher atomicity or nanoparticles, such as Cu-5 and Cu-20, are easily oxidized in the presence of O-2, leading to very stable reactive O atoms, resulting in low reactivity and selectivity in many oxidation reactions. Altogether, Cu-5, clusters are proposed as promising catalysts for catalytic applications where stabilization of metallic copper species is strongly required. ; The authors thank the MINECO (Consolider Ingenio 2010-MULTICAT CSD2009-00050 and Severo Ochoa program SEV-2012-0267), Generalitat Valenciana (PROMETEOII/2013/011 Project), and European Union (ERC-AdG-2014-671093-SynCatMatch) for financial support. E.F. and S.G.-G. thank the MINECO for their fellowship SVP-2013-068146 and financial support through project MAT2011-28009, respectively. ; Concepción Heydorn, P.; Boronat Zaragoza, M.; García García, S.; Fernández-Villanueva, E.; Corma Canós, A. (2017). Enhanced Stability of Cu Clusters of Low Atomicity against Oxidation. Effect on the Catalytic Redox Process. ACS Catalysis. 7(5):3560-3568. https://doi.org/10.1021/acscatal.7b00778 ; S ; 3560 ; 3568 ; 7 ; 5

This paper focuses on the design of an innovative air-conditioning system, namely a magnetocaloric air-conditioner for an electric minibus. An integrated design of the complete system is necessary, as the hot and cold side of the regenerator will work under dynamic conditions which depend on the instantaneous thermal load in the cabin. In order to assist the design of the system, a dynamic model has been developed for the cabin, the hydraulic loops and heat exchangers, and the magnetocaloric unit. This paper presents (i) a description of the dynamic models, (ii) an analysis of the operating conditions of the magnetocaloric unit and (iii) a discussion on the design of the magnetocaloric air-conditioner. The results show that the electric minibus requests 1.60 kW of cooling power over a span of 37 K in cooling mode, and 3.39 kW of heating power over a span of 40 K. ; This work has been supported by Haldor-Topsoe, the Spanish Government through Consolider Ingenio 2010-Multicat, the "Severo Ochoa Program", and MAT2012-37160. Manuel Moliner also acknowledges to "Subprograma Ramon y Cajal" for the contract RYC-2011-08972. The authors thank Isabel Millet for technical support. ; Martínez Franco, R.; Moliner Marin, M.; Concepción Heydorn, P.; Thogersen, JR.; Corma Canós, A. (2014). Synthesis, characterization and reactivity of high hydrothermally stable Cu-SAPO-34 materials prepared by one-pot processes. Journal of Catalysis. 314:73-82. https://doi.org/10.1016/j.jcat.2014.03.018 ; S ; 73 ; 82 ; 314

[EN] The structure of UiO-66(Ce) is formed by CeO2-x defective nanoclusters connected by terephthalate ligands. The initial presence of accessible Ce3+ sites in the as-synthesized UiO-66(Ce) has been determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR)-CO analyses. Moreover, linear scan voltammetric measurements reveal a reversible Ce4+/Ce3+ interconversion within the UiO-66(Ce) material, while nanocrystalline ceria shows an irreversible voltammetric response. This suggests that terephthalic acid ligands facilitate charge transfer between subnanometric metallic nodes, explaining the higher oxidase-like activity of UiO-66(Ce) compared to nanoceria for the mild oxidation of organic dyes under aerobic conditions. Based on these results, we propose the use of Ce-based metal-organic frameworks (MOFs) as efficient catalysts for the halogenation of activated arenes, as 1,3,5-trimethoxybenzene (TMB), using oxygen as a green oxidant. Kinetic studies demonstrate that UiO-66(Ce) is at least three times more active than nanoceria under the same reaction conditions. In addition, the UiO-66(Ce) catalyst shows an excellent stability and can be reused after proper washing treatments. Finally, a general mechanism for the oxidative halogenation reaction is proposed when using Ce-MOF as a catalyst, which mimics the mechanistic pathway described for metalloenzymes. The superb control in the generation of subnanometric CeO2-x defective clusters connected by adequate organic ligands in MOFs offers exciting opportunities in the design of Ce-based redox catalysts. ; This work has been supported by the Spanish Government through the "Severo Ochoa" (SEV-2016-0683, MINECO) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE). J. M. Salas is acknowledged for his contribution to CO-IR experiments. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. ; Rojas-Buzo, S.; Concepción Heydorn, P.; Olloqui-Sariego, JL.; Moliner Marin, M.; Corma Canós, A. (2021). ...

[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] The thermal transformation of hydrothermally prepared Cs-Nb-W-O mixed oxides has been studied in the 25-1000 degrees C temperature range. Structural evolution of the prepared solids was monitored by in situ synchrotron X-ray diffraction, absorption spectroscopy techniques, conventional powder X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, and high resolution transmission electron microscopy (HRTEM and STEM). The as-grown solids show the hexagonal tungsten bronze (HTB) structure, which can be stabilized above 900 degrees C depending on the chemical composition. From this temperature, solids are selectively transformed into the orthorhombic Cs-0.5(Nb2.5W2.5)O-14 structure-type. The same results are obtained for Cs-0.5(Nb2.5W2.5-xMx)O-3, with M = V or Mo (x = 0-1.25). A mechanism for the quantitative transformation at high temperature is proposed in terms of the relative occupancy of the hexagonal channels in the HTB-type phase as well as the Nb/(W + V) ratio. ; M.D.S. and J.M.L.N. acknowledge the Spanish Government-MINECO projects (CTQ2015-68951-C3-1-R and SEV-2016-0683). E.G.G. acknowledges the financial support through Projects MAT2013-46452-C4 and MAT2016-78362-C4-4-R and the valuable help of Dr. Urones-Garrote in STEM performing. Authors thank the ICTS Centro Nacional de Microscopia Electronica (UCM) for instrumental facilities and LNLS/CNPEM-Brazil for the synchrotron radiation facilities. ; Soriano Rodríguez, MD.; Garcia-Gonzalez, E.; Concepción Heydorn, P.; Rodella, C.; López Nieto, JM. (2017). The Self-Organized Transformation from Hexagonal to Orthorhombic Bronze of Cs-Nb-W-O Mixed Oxides Prepared Hydrothermally. Crystal Growth & Design. 17(12):6320-6331. https://doi.org/10.1021/acs.cgd.7b00999 ; S ; 6320 ; 6331 ; 17 ; 12

[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 ...