State of the art of Lewis acid-containing zeolites: lessons from fine chemistry to new biomass transformation processes

[EN] The former synthesis of TS-1 opened new catalytic opportunities for zeolites, especially for their application as selective redox catalysts in several fine chemistry processes. Interestingly, isolated Ti species in the framework positions of hydrophobic zeolites, such as high silica zeolites, offer unique Lewis acid sites even in the presence of protic polar solvents (such as water). Following this discovery, other transition metals (such as Sn, Zr, V, Nb, among others) have been introduced in the framework positions of different hydrophobic zeolitic structures, allowing their application in new fine chemistry processes as very active and selective redox catalysts. Recently, these hydrophobic metallozeolites have been successfully applied as efficient catalysts for several biomass-transformation processes in bulk water. The acquired knowledge from the former catalytic descriptions in fine chemistry processes using hydrophobic Lewis acid-containing zeolites has been essential for their application in these novel biomass transformations. In the present review, I will describe the recent advances in the synthesis of new transition metal-containing zeolites presenting Lewis acid character, and their unique catalytic applications in both fine chemistry and novel biomass-transformations.This work has been supported by the Spanish Government-MINECO (MAT2012-37160), Consolider Ingenio 2010-Multicat, and UPV through PAID-06-11 (no. 1952). Manuel Moliner also acknowledges the "Subprograma Ramon y Cajal" for the contract RYC-2011-08972. ITQ thanks the "Program Severo Ochoa" for financial support.Moliner Marin, M. (2014). State of the art of Lewis acid-containing zeolites: lessons from fine chemistry to new biomass transformation processes. Dalton Transactions. 43:4197-4208. https://doi.org/10.1039/C3DT52293HS419742084

Advances in the synthesis of titanosilicates: From the medium pore TS-1 zeolite to highly-accessible ordered materials

[EN] In the present review, we would like to cover the most fundamental advances achieved in the design of ordered titanosilicates since the earlier discovery of TS-1 reported by EniChem in the mid-eighties. The invention of the medium-pore TS-1 zeolite was a breakthrough, and this material has been applied as efficient catalyst in diverse industrial applications. However, its limited pore size (5 5.5 Å) offers diffusion limitations when working with large molecules. The design and preparation of open titanosilicates, such as large pore molecular sieves, mesoporous ordered materials, or layered-type zeolites will be described. The applicability of these titanosilicates to catalytic oxidation processes requiring bulky organic molecules will also be presented.This work has been supported by the Spanish GovernmentMINECO (MAT2012-37160), Consolider Ingenio 2010-Multicat, and UPV through PAID-06-11 (n.1952). Manuel Moliner also acknowledges to ‘‘Subprograma Ramon y Cajal’’ for the contract RYC-2011-08972. ITQ thanks the ‘‘Program Severo Ochoa’’ for financial support (SEV 2012 0267).Moliner Marin, M.; Corma Canós, A. (2014). Advances in the synthesis of titanosilicates: From the medium pore TS-1 zeolite to highly-accessible ordered materials. Microporous and Mesoporous Materials. 189:31-40. https://doi.org/10.1016/j.micromeso.2013.08.003S314018

Síntesis de nuevos materiales microporosos mediante técnicas de alta capacidad ("High-Throughput")

La presente tesis doctoral está enmarcada dentro del campo de la síntesis de materiales microporosos, los cuales presentan aplicaciones de diversa índole como separación de gases, catalizadores selectivos, electrónica, y biomedicina. Las zeolitas son materiales microporosos cristalinos, que presentan canales y cavidades de dimensiones moleculares en su interior. La gran ventaja de las zeolitas es su elevada estabilidad térmica y química, junto con la posibilidad de poder variar la topología y dimensiones de los canales y cavidades. El principal objetivo de la presente tesis doctoral es crear una nueva metodología de trabajo en la síntesis de materiales microporosos mediante el uso de técnicas de alta capacidad ("high-throughput"). El uso de este tipo de herramientas es muy reciente en el área de materiales y, por tanto, la aplicación de las mismas para el desarrollo de nuevos materiales de interés está en su primera etapa. Una vez desarrollada y comprobada la metodología de trabajo, se explota con el fin de descubrir nuevos materiales microporosos o mejorar las condiciones de preparación de los ya conocidos. Se estudia el efecto de los agentes directores de estructura orgánicos (rigidez y flexibilidad), la introducción de otros elementos tetravalentes distintos al silicio (Ge ó Ti), la presencia de elementos trivalentes que introducen cargas negativas en la red (como Al ó B), el agente mineralizante utilizado en la síntesis (medio OH- y medio F-), así como la concentración de los geles. Finalmente, el uso de las técnicas de alta capacidad genera una gran cantidad de resultados, que habrá que tratar mediante la utilización de técnicas de tratamiento de datos. En la parte final de la tesis, se desarrollan técnicas novedosas de tratamiento de datos en la síntesis de materiales, tanto a nivel de modelado, como de visualización y clasificación de los mismos.Moliner Marin, M. (2008). Síntesis de nuevos materiales microporosos mediante técnicas de alta capacidad ("High-Throughput") [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1987Palanci

Direct synthesis of functional zeolitic materials

[EN] Recently, the direct synthesis of zeolitic materials has received much attention because several well-defined functionalities have been introduced in those materials by “one-pot” methodologies. The rationalization of the physics and chemistry of the processes involved in the zeolite growth has allowed the direct preparation of different functional molecular sieves with unique properties and potential applicability in industry. In the present paper, the “one-pot” preparations of metal-containing zeolites (both in framework and extra-framework positions), hybrid organic-inorganic molecular sieves, hierarchical microporous mesoporous zeotypes, nanosheets, nanozeolites, or template-free molecular sieves are intensively evaluated.Financial support by the Spanish MINECO (MAT2012-37160), Consolider Ingenio 2010-Multicat, and UPV through PAID-06-11 (n. 1952) is acknowledged. The author also acknowledges “Subprograma Ramon y Cajal” for the contract RYC-2011-08972, and Dr. Cristina Mart´ınez and Dr. Pedro Serna for helpful discussions.Moliner Marin, M. (2012). Direct synthesis of functional zeolitic materials. ISRN Materials Science. (789525):1-24. https://doi.org/10.5402/2012/789525S12478952

Direct synthesis of a titanosilicate molecular sieve containing large and medium pores in its structure

[EN] The direct synthesis of the titanosilicate form of ITQ-39 is reported. This is the first description of the direct preparation of a titanosilicate molecular sieve containing large and medium pores in the same structure. The characterization clearly indicates the presence of Ti atoms in tetrahedral coordination in the framework of ITQ-39 zeolite. This material is very active in the oxidation of lineal and cyclic olefins with H2O2, showing selectivities between TS-1 and Ti-Beta. (C) 2012 Elsevier Inc. All rights reserved.Financial support by the Spanish MEC (Consolider Ingenio 2010-Multicat), Generalitat Valenciana by the PROMETEO program and UPV through PAID-06-11 (n.1952) is acknowledged. Manuel Moliner acknowledges to "Subprograma Ramon y Cajal" for the contract RYC-2011-08972. Jose Gaona is also acknowledged for technical help.Moliner Marin, M.; Corma Canós, A. (2012). Direct synthesis of a titanosilicate molecular sieve containing large and medium pores in its structure. Microporous and Mesoporous Materials. 164:44-48. https://doi.org/10.1016/j.micromeso.2012.06.035S444816

Machine Learning Applied to Zeolite Synthesis: The Missing Link for Realizing High-Throughput Discovery

[EN] CONSPECTUS: Zeolites are microporous crystalline materials with well-defined cavities and pores, which can be prepared under different pore topologies and chemical compositions. Their preparation is typically defined by multiple interconnected variables (e.g., reagent sources, molar ratios, aging treatments, reaction time and temperature, among others), but unfortunately their distinctive influence, particularly on the nucleation and crystallization processes, is still far from being understood. Thus, the discovery and/or optimization of specific zeolites is closely related to the exploration of the parametric space through trial-and-error methods, generally by studying the influence of each parameter individually. In the past decade, machine learning (ML) methods have rapidly evolved to address complex problems involving highly nonlinear or massively combinatorial processes that conventional approaches cannot solve. Considering the vast and interconnected multiparametric space in zeolite synthesis, coupled with our poor understanding of the mechanisms involved in their nucleation and crystallization, the use of ML is especially timely for improving zeolite synthesis. Indeed, the complex space of zeolite synthesis requires draWing inferences from incomplete and imperfect information, for which ML methods are very well-suited to replace the intuition-based approaches traditionally used to guide experimentation. In this Account, we contend that both existing and new ML approaches can provide the "missing link" needed to complete the traditional zeolite synthesis workflow used in our quest to rationalize zeolite synthesis. Within this context, we have made important efforts on developing ML tools in different critical areas, such as (1) data-mining tools to process the large amount of data generated using high-throughput platforms; (2) novel complex algorithms to predict the formation of energetically stable hypothetical zeolites and guide the synthesis of new zeolite structures; (3) new "ab initio" organic structure directing agent predictions to direct the synthesis of hypothetical or known zeolites; (4) an automated tool for nonsupervised data extraction and classification from published research articles. ML has already revolutionized many areas in materials science by enhancing our ability to map intricate behavior to process variables, especially in the absence of well-understood mechanisms. Undoubtedly, ML is a burgeoning field with many future opportunities for further breakthroughs to advance the design of molecular sieves. For this reason, this Account includes an outlook of future research directions based on current challenges and opportunities. We envision this Account will become a hallmark reference for both well-established and new researchers in the field of zeolite synthesis.This work has been supported by the EU through ERC-AdG2014-671093, by the Spanish Government through SEV-20160683 and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE), and by La Caixa-Foundation through MIT -SPAIN MISTI program (LCF/PR/MIT17/11820002). Y.R.-L. thanks the DoE for funding through the Office of Basic Energy Sciences (DE-SC0016214).Moliner Marin, M.; Román-Leshkov, Y.; Corma Canós, A. (2019). Machine Learning Applied to Zeolite Synthesis: The Missing Link for Realizing High-Throughput Discovery. Accounts of Chemical Research. 52(10):2971-2980. https://doi.org/10.1021/acs.accounts.9b00399S29712980521

Influence of Preparation Conditions on the Catalytic Performance of Mo/H-ZSM-5 for Methane Dehydroaromatization

[EN] Methane, the main component of natural gas, is an interesting source of chemicals and clean liquid fuels, and a promising alternative raw material to oil. Among the possible direct routes for methane conversion, its aromatization under non-oxidative conditions has received increasing attention, despite the low conversions obtained due to thermodynamic limitations, because of its high selectivity to benzene. Mo/H-ZSM-5, the first bifunctional zeolite-catalyst proposed for this reaction, is still considered as one of the most adequate and has been widely studied. Although the mono- or bifunctional nature of the MDA mechanism is still under debate, it is generally accepted that the Mo species activate the C-H bond in methane, producing the intermediates. These will aromatize on the Bronsted acid sites of the zeolite, whose pore dimensions will provide the shape selectivity needed for converting methane into benzene. An additional role of the zeolite's Bronsted acid sites is to promote the dispersion of the Mo oxide precursor. Here, we show the influence of the different preparation steps-metal incorporation, calcination and activation of the Mo/ZSM-5- on the metal dispersion and, therefore, on the activity and selectivity of the final catalyst. Metal dispersion is enhanced when the samples are calcined under dynamic conditions (DC) and activated in N-2, and the benefits are larger when the metal has been incorporated by solid state reaction (SSR), as observed by FESEM-BSE and H-2-TPR. This leads to catalysts with higher activity, increased aromatic selectivity and improved stability towards deactivation.This work has been supported by the Spanish Government-MICINN through "Severo Ochoa" (SEV-2016-0683, MINECO) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE), and by Generalitat Valenciana (AICO/2019/060). The authors thank B. Esparcia for technical assistance and the electron Microscopy Service of the UPV for their help in sample characterization.Portilla, MT.; Llopis, FJ.; Moliner Marin, M.; Martínez, C. (2021). Influence of Preparation Conditions on the Catalytic Performance of Mo/H-ZSM-5 for Methane Dehydroaromatization. Applied Sciences. 11(12):1-17. https://doi.org/10.3390/app11125465S117111

Coordinatively Unsaturated Hf-MOF-808 Prepared via Hydrothermal Synthesis as a Bifunctional Catalyst for the Tandem N-Alkylation of Amines with Benzyl Alcohol

[EN] The modulated hydrothermal (MHT) synthesis of an active and selective Hf-MOF-808 material for the N-alkylation reaction of aniline with benzyl alcohol under base-free mild reaction conditions is reported. Through kinetic experiments and isotopically labeled NMR spectroscopy studies, we have demonstrated that the reaction mechanism occurs via borrowing hydrogen (BH) pathway, in which the alcohol dehydrogenation is the limiting step. The high concentration of defective -OH groups generated on the metallic nodes through MHT synthesis enhances the alcohol activation, while the unsaturated Hf4+, which acts as a Lewis acid site, is able to borrow the hydrogen from the methylene position of benzyl alcohol. This fact makes this material at least 14 times more active for the N-alkylation reaction than the material obtained via solvothermal synthesis. The methodology described in this work could be applied to a wide range of aniline and benzyl alcohol derivates, showing in all cases high selectivity toward the corresponding N-benzylaniline product. Finally, Hf-MOF-808, which acts as a true heterogeneous catalyst, can be reused in at least four consecutive runs without any activity loss.This work has been supported by Spanish Government through "severo Ochoa" (SEV-2016-0683, MINECO) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE). The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization.Bohigues, B.; Rojas-Buzo, S.; Moliner Marin, M.; Corma Canós, A. (2021). Coordinatively Unsaturated Hf-MOF-808 Prepared via Hydrothermal Synthesis as a Bifunctional Catalyst for the Tandem N-Alkylation of Amines with Benzyl Alcohol. ACS Sustainable Chemistry & Engineering. 9(47):15793-15806. https://doi.org/10.1021/acssuschemeng.1c04903157931580694

Unraveling the Reaction Mechanism and Active Sites of Metal-Organic Frameworks for Glucose Transformations in Water: Experimental and Theoretical Studies

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry & Engineering, 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/acssuschemeng.0c04398[EN] The catalytic performance of two different MOFs, UiO-66 and MOF-808, containing Lewis acid active sites has been evaluated for the transformation of glucose in water and compared with that of analogous Lewis acid Zr-beta zeolite. While fructose is the main product obtained on Zr-beta, mannose production increases when using Zr-MOFs as catalysts. Kinetic studies reveal a lower activation energy barrier for glucose epimerization to mannose when using Zr-MOF catalysts (similar to 83-88 and similar to 100 kJ/mol for glucose epimerization and isomerization, respectively). A C-13 NMR study using (13)C1-labeled glucose allows confirming that on Zr-MOF catalysts, mannose is exclusively formed following the glucose epimerization route through a 1,2-intramolecular carbon shift, whereas the two-step glucose -> fructose -> mannose isomerization via 1,2-intramolecular proton shifts is the preferred pathway on Zr-beta. A computational study reveals a different mode of adsorption of deprotonated glucose on Zr-MOFs that allows decreasing the activation barrier for the 1,2-intramolecular carbon shift. The combination of spectroscopic, kinetic, and theoretical studies allows unraveling the nature of the metal sites in Zr-MOFs and Zr-beta catalysts and to propose a structure-activity relationship between the different Lewis acid sites and the glucose transformation reactions. The results presented here could permit new rationalized MOF catalyst designs with the specific active sites to facilitate particular reaction mechanisms.This work was supported by the Spanish Government through "Severo Ochoa"(SEV-2016-0683, MINECO), MAT2017-82288-C2-1-P (AEI/FEDER, UE), and RTI2018-101033-BI00 (MCIU/AEI/FEDER, UE); and by Generalitat Valenciana through AICO/2019/060. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization.Rojas-Buzo, S.; Corma Canós, A.; Boronat Zaragoza, M.; Moliner Marin, M. (2020). Unraveling the Reaction Mechanism and Active Sites of Metal-Organic Frameworks for Glucose Transformations in Water: Experimental and Theoretical Studies. ACS Sustainable Chemistry & Engineering. 8(43):16143-16155. https://doi.org/10.1021/acssuschemeng.0c04398S1614316155843Gallezot, P. (2012). Conversion of biomass to selected chemical products. Chem. Soc. 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Trapping of Metal Atoms and Metal Clusters by Chabazite under Severe Redox Stress

[EN] The remarkable ability of Al-containing CHA zeolite to trap and stabilize noble single-metal atoms and metal clusters has facilitated the design of sinter-resistant materials for catalytic applications that require severe reaction conditions. At high temperatures in O-2, volatile MOx species appear to be fixated by the zeolite Al centers to prevent Ostwald-ripening sintering mechanisms, whereas small metal clusters (<100 atoms) are stabilized in H-2 without further aggregation as coalescence by Brownian motion is inhibited because of an encapsulation effect. Evidences of the possibility to trap the metal released from a second adjacent surface (e.g., SiO2 and Al2O3), upon metal migration over micrometer distances, are provided. These properties have opened the possibility to prepare several noble-metal atoms and clusters inside small-pore zeolites, including bimetallic formulation, by simple wetness impregnations or solid-to-solid transformations followed by standard calcination procedures, resulting in improved catalytic performances compared to other nonreducible supports in reactions that subject the catalysts to severe redox stress, such as the water-gas-shift reaction.This work has been supported by the Spanish Government-MINECO through "Severo Ochoa" (SEV 2012-0267) and MAT2015-71261-R, by the European Union through ERC-AdG-2014-671093 (SynCatMatch) and by the Fundacion Ramon Areces through a research contract of the "Life and Materials Science" program. The Electron Microscopy Service of the UPV is acknowledged for their help in sample characterization. This research used beamline 9-BM and 20-ID of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank Isabel Millet, Elisa Garcia, and Paul Stevens for technical assistance, and Aaron Sattler, Randall Meyer, Rob Carr, and Gary Casty for review of the manuscript and interesting scientific discussions. We appreciate the support of ExxonMobil Research and Engineering in this fundamental research area.Moliner Marin, M.; Gabay, JE.; Kliewer, CE.; Serna Merino, PM.; Corma Canós, A. (2018). Trapping of Metal Atoms and Metal Clusters by Chabazite under Severe Redox Stress. ACS Catalysis. 8(10):9520-9528. https://doi.org/10.1021/acscatal.8b01717S9520952881