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Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner. ; Financial support from the European Union through theEuropean Research Council (grant ERC-AdG-2014-671093,SynCatMatch) and the Spanish government through the"SeveroOchoa Program"(SEV-2016-0683) is acknowledged.

[EN] Activation of alkanes can be achieved with different types of catalysts, spanning over enzymes, homogeneous and heterogeneous metal catalysts. Though a tremendous amount of knowledge has been accumulated in the literature, the connections between different types of catalysts are rarely discussed due to the differences among the three catalysis fields in terms of catalyst structures, reaction conditions, and catalytic performances. There are also similarities among the various systems in terms of the structural features of the active sites and reaction mechanisms. In this review, we attempt to show the interconnections among the three catalysis fields regarding the nature of active sites and reaction mechanism for metal-catalyzed alkane activation reactions. We will show the lessons obtained from well-defined enzymatic and molecular catalysts developed in bio- and homogeneous catalysis, and how these can be translated into fundamental understanding and further developments of heterogeneous metal catalysts, for practical applications related to alkane activation. ; We are grateful for the financial supports from the Spanish Government through the "Severo Ochoa Program'' (SEV-2016-SEV-0683). ; Liu, L.; Corma Canós, A. (2021). Isolated metal atoms and clusters for alkane activation: translating knowledge from enzymatic and homogeneous to heterogeneous systems. Chem. 7(9):2347-2384. https://doi.org/10.1016/j.chempr.2021.04.001 ; S ; 2347 ; 2384 ; 7 ; 9

[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

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 http://doi.org/10.1021/acscatal.7b00170 ; [EN] Nanolayered molybdenum disulfide cobalt-promoted materials (Co-Mo-S) have been established as chemoselective catalysts for thehydrogenation of nitroarenes under relatively mild conditions. Co-Mo-S catalysts have been prepared by a one-pot hydrothermal synthesis that allows the formation of unsupported catalysts with a large number of active sites per unit volume. Via application of these catalysts, the hydrogenation of the nitro functionality has been performed selectively in the presence of double and triple bonds, aldehydes, ketones, and carboxylic acid derivative groups, thus affording the corresponding anilines in good to excellent yields. Interestingly, the partial hydrogenation of some dinitroarenes has also been successfully accomplished. In addition, its catalytic performance has been evaluated for the preparation of the bioactive compound paracetamol through a one-pot direct hydrogenative amidation reaction. ; The financial support of the European Union (FP7-NMP-2013-EU-Japan-604319-NOVACAM) is gratefully acknowledged. I.S. thanks Spanish MINECO for a "Formacion Postdoctoral" fellowship. The authors also thank the Microscopy Service of Universitat Politecnica de Valencia for kind help with TEM and STEM measurements. ; Sorribes-Terrés, I.; Liu, L.; Corma Canós, A. (2017). Nanolayered Co-Mo-S Catalysts for the Chemoselective Hydrogenation of Nitroarenes. ACS Catalysis. 7(4):2698-2708. https://doi.org/10.1021/acscatal.7b00170 ; S ; 2698 ; 2708 ; 7 ; 4

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

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

[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 document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/acscatal.7b04260 ; [EN] Herein, a general protocol for the preparation of a broad range of valuable N-heterocyclic products by hydrogenation of quinolines and related N-heteroarenes is described. Interestingly, the catalytic hydrogenation of the N-heteroarene ring is chemoselectively performed when other facile reducible functional groups, including alkenes, ketones, cyanides, carboxylic acids, esters, and amides, are present. The key to successful catalysis relies on the use of a nanolayered cobalt-molybdenum sulfide catalyst hydrothermally synthesized from earth-abundant metal precursors. This heterogeneous system displays a tunable composition of phases that allows for catalyst regeneration. Its catalytic activity depends on the composition of the mixed phase of cobalt sulfides, being higher with the presence of Co3S4, and could also be associated with the presence of transient Co-Mo-S structures that mainly vanish after the first catalytic run. ; Financial support by the Spanish Government-MINECO through the program "Severo Ochoa" (SEV-2016-0683) is gratefully acknowledged. I.S. also thanks the Spanish Government-MINECO for a "Formacion Postdoctoral" fellowship and Vice-Rectorate for Research, Innovation and Transfer of the Universitat Politecnica de Valencia (UPV) for a postdoctoral fellowship. The authors also thank the Microscopy Service of UPV for kind help with TEM and STEM measurements. ; Sorribes, I.; Liu, L.; Doménech Carbó, A.; Corma Canós, A. (2018). Nanolayered Cobalt-Molybdenum Sulfides as Highly Chemo- and Regioselective Catalysts for the Hydrogenation of Quinoline Derivatives. ACS Catalysis. 8(5):4545-4557. https://doi.org/10.1021/acscatal.7b04260 ; S ; 4545 ; 4557 ; 8 ; 5

4545 4557 8 5 ; S ; This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/acscatal.7b04260 [EN] Herein, a general protocol for the preparation of a broad range of valuable N-heterocyclic products by hydrogenation of quinolines and related N-heteroarenes is described. Interestingly, the catalytic hydrogenation of the N-heteroarene ring is chemoselectively performed when other facile reducible functional groups, including alkenes, ketones, cyanides, carboxylic acids, esters, and amides, are present. The key to successful catalysis relies on the use of a nanolayered cobalt-molybdenum sulfide catalyst hydrothermally synthesized from earth-abundant metal precursors. This heterogeneous system displays a tunable composition of phases that allows for catalyst regeneration. Its catalytic activity depends on the composition of the mixed phase of cobalt sulfides, being higher with the presence of Co3S4, and could also be associated with the presence of transient Co-Mo-S structures that mainly vanish after the first catalytic run. Financial support by the Spanish Government-MINECO through the program "Severo Ochoa" (SEV-2016-0683) is gratefully acknowledged. I.S. also thanks the Spanish Government-MINECO for a "Formacion Postdoctoral" fellowship and Vice-Rectorate for Research, Innovation and Transfer of the Universitat Politecnica de Valencia (UPV) for a postdoctoral fellowship. The authors also thank the Microscopy Service of UPV for kind help with TEM and STEM measurements. Sorribes, I.; Liu, L.; Doménech Carbó, A.; Corma Canós, A. (2018). Nanolayered Cobalt-Molybdenum Sulfides as Highly Chemo- and Regioselective Catalysts for the Hydrogenation of Quinoline Derivatives. ACS Catalysis. 8(5):4545-4557. https://doi.org/10.1021/acscatal.7b04260

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 ∼5 nm without using bulk capping agent. Structural and surface characterizations show that the chemical states of CuOx nanoparticles and their interactions with O 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 (∼2 nm) were used as catalyst. Supported CuOx nanoparticles on TiO behave in the same way as monodispersed CuOx nanoparticles. Kinetic, spectroscopic, and isotopic studies show that O 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. ; Financial supports from ConsoliderIngenio 2010 (project MULTICAT) and "Severo Ochoa" program are also gratefully acknowledged. The European Union is also acknowledged by ERC-AdG-2014-671093 - SynCatMatch. ; Peer Reviewed

[EN] The encapsulation of subnanometric metal entities (isolated metal atoms and metal clusters with a few atoms) in porous materials such as zeolites can be an effective strategy for the stabilization of those metal species and therefore can be further used for a variety of catalytic reactions. However, owing to the complexity of zeolite structures and their low stability under the electron beam, it is challenging to obtain atomic-level structural information of the subnanometric metal species encapsulated in zeolite crystallites. In this protocol, we show the application of a scanning transmission electron microscopy (STEM) technique that records simultaneously the high-angle annular dark-field (HAADF) images and integrated differential phase-contrast (iDPC) images for structural characterization of subnanometric Pt and Sn species within MFI zeolite. The approach relies on the use of a computational model to simulate results obtained under different conditions where the metals are present in different positions within the zeolite. This imaging technique allows to obtain simultaneously the spatial information of heavy elements (Pt and Sn in this work) and the zeolite framework structure, enabling direct determination of the location of the subnanometric metal species. Moreover, we also present the combination of other spectroscopy techniques as complementary tools for the STEM-iDPC imaging technique to obtain global understanding and insights on the spatial distributions of subnanometric metal species in zeolite structure. These structural insights can provide guidelines for the rational design of uniform metal-zeolite materials for catalytic applications. Precise knowledge of the structure of metals supported and stabilized by zeolite frameworks informs improved design and synthesis of the catalysts. This tutorial describes scanning transmission electron microscopy approaches for their structural analysis. ; This work was supported by the European Union through the European Research Council (grant ...

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).

[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