Spiers Memorial Lecture ; Taking the chemoselective hydrogenation of substituted nitroaromatics as a base case, it will be shown that it is possible to design improved and new catalysts by attacking the problem in a multidisciplinary way. By combining molecular modeling with in situ operando spectroscopy, and with micro-kinetic and isotopic studies, it is possible to determine how and where on the catalysts the reactant molecules interact. Then, materials synthesis methods can be applied to prepare catalysts with the desired surface active sites and their selective interaction with the reactants. ; This work was funded by the Spanish Government (Severo Ochoa program SEV2012-0267). The support of the European Union by (ERC-AdG-2014-671093 – SynCatMatch) is also acknowledged. ; Peer Reviewed
Based on theoretical calculations of CO, NH, and pyridine adsorption at different sites in MOR and MFI zeolites, we analyze how confinement effects influence the measurement of acidity based on the interaction of probe molecules with Brönsted acid sites. Weak bases, such as CO, form neutral ZH-CO adducts with a linear configuration that can be distorted by spatial restrictions associated with the dimensions of the pore, leading to weaker interaction, but can also be stabilized by dispersion forces if a tighter fitting with the channel void is allowed. Strong bases such as NH and pyridine are readily protonated on Brönsted acid sites, and the experimentally determined adsorption enthalpies include not only the thermochemistry associated with the proton transfer process itself, but also the stabilization of the Z-BH ion pair formed upon protonation by multiple interactions with the surrounding framework oxygen atoms, leading in some cases to a heterogeneity of acidities within the same zeolite structure. ; This work was supported by the European Union through No. ERC-AdG-2014-671093 (SynCatMatch), and by the Spanish Government-MINECO through "Severo Ochoa" (No. SEV-2016-0683) and No. MAT2017-82288-C2-1-P projects. Red Española de Supercomputación (RES) and Centre de Càlcul de la Universitat de València are gratefully acknowledged for computational resources.
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.
The design of new hybrid materials with tailored properties at the nano-, meso-, and macro-scale, with the use of structural functional nanobuilding units, is carried out to obtain specific multi-functional materials. Organization into controlled 1D, 2D, and 3D architectures with selected functionalities is key for developing advanced catalysts, but this is hardly accomplished using conventional synthesis procedures. The use of pre-formed nanostructures, derived either from known materials or made with specific innovative synthetic methodologies, has enormous potential in the generation of multi-site catalytic materials for one-pot processes. The present concept article introduces a new archetype wherein self-assembled nanostructured builder units are the base for the design of multifunctional catalysts, which combine catalytic efficiency with fast reactant and product diffusion. The article addresses a new generation of versatile hybrid organic-inorganic multi-site catalytic materials for their use in the production of (chiral) high-added-value products within the scope of chemicals and fine chemicals production. The use of those multi-reactive solids for more nanotechnological applications, such as sensors, due to the inclusion of electron donor-acceptor structural arrays is also considered, together with the adsorption-desorption capacities due to the combination of hydrophobic and hydrophilic sub-domains. The innovative structured hybrid materials for multipurpose processes here considered, can allow the development of multi-stage one-pot reactions with industrial applications, using the materials as one nanoreactor systems, favoring more sustainable production pathways with economic, environmental and energetic advantages. ; The authors are grateful for financial support from the Spanish Government by MAT2014‐52085‐C2‐1‐P and Severo Ochoa Excellence Program SEV‐2016‐0683. The European Union is also acknowledged by ERC‐AdG‐2014‐671093‐SynCatMatch.
Covalent organic frameworks, COFs, and their derived sub-groups based on auto-assembly of exclusively aromatic units, PAFs, are emerging into the advanced materials field due to their high free porous volume, structural regularity, robustness, hydrothermal stability, and functional variety. They present high gas uptake capacities and presence of stabilized active functions in the framework. This together with charged low-density structures combined with their organization through π-conjugated system arrays, open the possibilities of COFs and PAFs to be used as effective materials for adsorption, selective separation and catalysis, and in nanotechnological applications. This review will be focused on self-assembly synthesis mechanisms, physico-chemical characteristics, and applications of this class of promising covalent porous organic structures, out looking their possible future approaches and perspectives. ; This work was funded by the Spanish Government (Severo Ochoa program SEV-2012-0267 and MAT2014-52085-C2-1-P) and by the Generalitat Valenciana (Prometeo). The European Union is also acknowledged by ERC-AdG-2014-671093 – SynCatMatch. ; Peer Reviewed
The hydrogenation of nitro compounds is an industrial process that has experienced a renovated interest in the last 10 years due to the discovery of highly selective and environmentally friendly solid catalysts. Particularly, the performance of chemoselective reactions in the presence of very sensitive groups such as double and triple CC bonds, with H2 as reductant and no soluble additives needed, had been elusive for decades. The discovery that gold nanoparticles on solid supports could carry out such a reaction very selectively invigorated this area of research and claimed gold as an outstanding catalyst beyond oxidation processes. Subsequent work, devoted to understand how gold catalysts operate, established a strong basis for the design of more efficient materials and the development of new routes for the synthesis of nitro derivatives. Here, we present three generations of materials that allowed improving the performance of the original gold catalysts. The relatively low activity of the initial Au/TiO2 catalysts could be first boosted, without practical loss of selectivity, by the design of a material that incorporated two catalytic functions on the support: small amounts of platinum to enhance H2 dissociation and a greater amount of gold to activate the −NO2 group. Later, we learned how to control the catalytic structures and induce chemoselectivity to traditionally unselective metals such as platinum, ruthenium, and nickel nanoparticles. Recently, Fe2O3 nanoparticles surrounded by a nitrogen-doped carbon layer have erupted as a promising alternative. A remarkable outcome from all that work is that the final pool of catalytic alternatives has been markedly expanded. Diversity is important because different solutions may open new gates to different catalytic processes, and we summarize here how the scope of new reactions and products could be expanded by means of properly designed metal catalysts in which the support and metal work in a concerted way to direct the reaction toward the desired product. For example, whereas Au/TiO2 is a chemoselective catalyst that drives the reaction efficiently to the fully reduced reaction product (aniline), the reaction could be tuned to obtain azocompounds in high yields by using nanoparticulated ceria to support the gold nanoparticles. On the other hand, whereas nitrobenzenes and aldehydes react in H2 to afford imines in the presence of Au/TiO2, the product distribution can be switched toward a more oxidized condensation product (a nitrone) using a chemoselective Pt/C catalyst, or to produce cyclohexanone oxime directly from nitrobenzene by means of supported Au and Pd metal catalysts. These and other examples represent some notable achievements, which are possibly, just the tip of the iceberg. ; The research was supported by Project CONSOLIDER INGENIO (MULTICAT), PROMETEO, the SEVERO OCHOA Program for centers of excellence. P.S. thanks the "Subprograma Ramon y Cajal" for the contract RYC-2012-10662. The European Union is also acknowledged by ERCAdG-2014-671093 - SynCatMatch. ; Peer Reviewed
Novel bifunctional acid-base monolayered hybrid catalysts (MLHMs), based on associated individual (organo)aluminosilicate sheets with amino and sulfonic pending groups located in the interlayer space, have been successfully prepared by direct alkaline hydrothermal synthesis and evaluated in consecutive catalytic transformations. Different characterization techniques such as chemical and thermogravimetrical analyses, X-ray diffraction, TEM microscopy, nuclear magnetic resonance (NMR), temperature-programmed desorption of CO and NH (TPD), and textural measurements were used to show the physicochemical and structural nature of the materials, evidencing their effectiveness as functional acid, base, and acid-base catalysts for different one-pot two-step tandem reactions, which were performed in the presence of only one active and recoverable lamellar-type hybrid solid catalyst. ; The authors are grateful for financial support from the Spanish Government by MAT2014-52085-C2-1-P and Severo Ochoa Excellence Program SEV-2012-0267. A.G. thanks predoctoral fellowships from MINECO for economical support (reference number BES-2012-052429). The European Union is also acknowledged by ERC-AdG-2014-671093-SynCatMatch. ; Peer Reviewed
The interaction of small molecules with acid–base and redox centers in small Ce21O42 nanoparticles has been theoretically investigated using the DFT + U approach with the PW91 functional and U = 0.2 and 4 eV, in order to determine the influence of the U value on the trends observed in selected properties describing such interactions. CO adsorption at low coordinated Ce4 + Lewis acid centers, water adsorption and dissociation at acid–base pairs, formation of oxygen vacancy defects by removal of an oxygen atom from the system, and interaction of molecular O2 with such defects have been considered. The largest effect of the value of U is found for the description of the reduced Ce21O41 nanoparticle. In all other cases involving stoichiometric and oxidized Ce21O42 and Ce21O43 systems, the trends in the calculated adsorption and reaction energies, optimized geometries, charge distribution, and vibrational frequencies are quite similar at the three levels considered. ; Financial support from the Spanish Science and Innovation Ministry (Consolider Ingenio 2010-MULTICAT CSD2009-00050 and Subprograma de apoyo a Centros y Universidades de Excelencia Severo Ochoa SEV 2012 0267) is acknowledged. The European Union is also acknowledged by ERC-AdG-2014-671093 — SynCatMatch. Red Española de Supercomputación (RES) and Centre de Càlcul de la Universitat de València are gratefully acknowledged for computational facilities and technical assistance. T. L.-A. thanks ITQ for a contract. ; Peer Reviewed
The preparation of continuous layers of highly hydrophobic pure silica ITQ-29 zeolite, potentially applicable as hydrophobic membranes for separation of molecules based on their polarity, has been investigated. Continuous layers of intergrown ITQ-29 zeolite crystals were successfully grown on porous alumina supports by optimization of the synthesis conditions, such as the appropriate selection of the seeds, the procedure for the gel preparation, and the calcination conditions. This resulted in the formation of all silica ITQ-29 zeolite layers without the presence of germanium required in previously reported ITQ-29 membranes, with the subsequent improvement in quality and stability, as verified by the absence of cracks after calcination. We have proved that the incorporation of aluminum from the support into the zeolite layer does not occur, neither during the secondary growth nor through migration of aluminum species during calcination. ; This research was funded by the European Research Council, grant ERC-AdG-2014-671093 (SynCatMatch) and the Spanish Government, through "Severo Ochoa" grant SEV-2016-0683 and RTI2018-101784-B-I00
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
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
The hydrogenation activity and physico-chemical characterization of a series of NiMo catalyst supported on materials with different acid-base properties (AlO, layered double hydroxides-derived MgAl oxides and MgO) have been investigated. The results show a clear correlation between the electrodonor capacity of the support, the negative charge density of the supported NiMo oxides and the intrinsic hydrogenation rate of the sulfided phase. Spectroscopic characterization ruled out any possible contribution derived from differences in the NiMoS stack or slab size distributions, as determined by high-resolution transmission electron microscopy. The experimental results obtained suggest the occurrence of an electron transfer phenomena from the support to the supported NiMoS slabs, being this effect stronger for supports with higher electrodonor capacity. This work presents a specific electronic support effect that goes beyond the classical dispersing and stabilizing role. ; This work has been supported by ExxonMobil Research and Engineering and by the Spanish Government through RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE). We thank the Electron Microscopy Service of the UPV for their help in sample characterization.
The exploration of highly efficient catalysts based on nano-sized Ti-rich titanosilicate zeolites with controllable active titanium species is of great importance in zeolite catalytic reactions. Herein, we reported an efficient and facile synthesis of nano-sized Ti-rich TS-1 (MFI) zeolites by replacing tetrabutyl orthotitanate (TBOT) with tetrabutyl orthotitanate tetramer (TBOT-tetramer) as the titanium source. The introduced TBOT-tetramer slowed down the zeolite crystallization process, and accordingly balanced the rate of incorporating Ti and the crystal growth and inhibited the massive formation of anatase species. Notably, the prepared Ti-rich TS-1 zeolite sample had a Si/Ti as low as 27.6 in contrast to conventional one with a molar ratio of 40. The TBOT-tetramer endowed the titanosilicate zeolites with enriched active titanium species and enlarged external surface area. It also impeded the formation of anatase species, resulting in superior catalytic behavior toward the oxidative desulfurization of dibenzothiophene compared with the conventional TS-1 zeolite counterpart prepared with TBOT. ; The authors thank the National Natural Science Foundation of China, China (Grant 21920102005, 21621001, and 21835002), the 111 Project, China (B17020), the European Union through the European Research Council, European Union (grant ERC-AdG-2014-671093, SynCatMatch), and the Spanish Government through "Severo Ochoa", Spain (SEV-2016-0683, MINECO) for supporting this work. R. Bai acknowledges the financial support from China Scholarship Council, China. ; 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).
