What Is Measured When Measuring Acidity in Zeolites with Probe Molecules?

[EN] Based on theoretical calculations of CO, NH3, 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 NH3 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 Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational resources.Boronat Zaragoza, M.; Corma Canós, A. (2019). What Is Measured When Measuring Acidity in Zeolites with Probe Molecules?. 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The 2D or 3D morphology of sub-nanometer Cu-5 and Cu-8 clusters changes the mechanism of CO oxidation

[EN] The mechanism of the CO oxidation reaction catalysed by planar Cu-5, three dimensional (3D) Cu-5, and 3D Cu-8 clusters is theoretically investigated at the B3PW91/Def2TZVP level. All three clusters are able to catalyse the reaction with similar activation energies for the rate determining step, about 16-18 kcal mol(-1), but with remarkable differences in the reaction mechanism depending on cluster morphology. Thus, for 3D Cu-5 and Cu-8 clusters, O-2 dissociation is the first step of the mechanism, followed by two consecutive CO + O reaction steps, the second one being rate determining. In contrast, on planar Cu-5 the reaction starts with the formation of an OOCO intermediate in what constitutes the rate determining step. The O-O bond is broken in a second step, releasing the first CO2 and leaving one bi-coordinately adsorbed O atom which reacts with CO following an Eley-Rideal mechanism with a low activation energy, in contrast to the higher barriers obtained for this step on 3D clusters.This work was supported by the Spanish Government through ``Severo Ochoa Program'' (SEV-2016-0683), MAT2017-82288-C21-P and MCIN PID2020-112590GB-C21. We thank Red Espan~ola de Supercomputacio ' n (RES) and Centre de Ca`lcul de la Universitat de Valencia for computational resources and technical support. E. F. thanks the Spanish MINECO for her fellowship SVP-2013-068146.Fernández, E.; Boronat Zaragoza, M.; Corma Canós, A. (2022). The 2D or 3D morphology of sub-nanometer Cu-5 and Cu-8 clusters changes the mechanism of CO oxidation. Physical Chemistry Chemical Physics. 24(7):4504-4514. https://doi.org/10.1039/d1cp05166k4504451424

The Crucial Role of Cluster Morphology on the Epoxidation of Propene Catalyzed by Cu-5: A DFT Study

[EN] The selective oxidation of propene to propene oxide (PO) is an industrially relevant and still challenging reaction that requires the design of highly specific catalysts able to improve simultaneously activity and selectivity. Metallic copper exhibits high selectivity toward propene epoxidation that drops when the catalyst surface is oxidized under reaction conditions. On the basis of previous work showing that small planar Cu-5 clusters are more resistant to oxidation than 3D ones, we have performed a detailed theoretical study of the mechanism of propene oxidation with molecular O-2 and atomic O adsorbed on both planar and 3D Cu-5 clusters. The desired pathways leading to PO as well as the undesired routes producing propanal, acetone, or allyl intermediates that finally evolve to acrolein or CO2 have been considered, and the global analysis of all data indicates that planar Cu-5 clusters are promising candidates for the selective epoxidation of propeneThis work has been supported by the European Union through ERC-AdG-2014-671093 (SynCatMatch) and by the Spanish Government through "Severo Ochoa"(SEV-2016-0683, MINECO) and MAT2017-82288-C2-1-P (AEI/FEDER, UE) Projects. E.F.V. thanks Spanish MINECO for her fellowship SVP-2013-068146.Fernández Villanueva, E.; Boronat Zaragoza, M.; Corma Canós, A. (2020). The Crucial Role of Cluster Morphology on the Epoxidation of Propene Catalyzed by Cu-5: A DFT Study. The Journal of Physical Chemistry C. 124(39):21549-21558. https://doi.org/10.1021/acs.jpcc.0c06295S21549215581243

Structure-reactivity relationship in isolated Zr sites present in Zr-zeolite and ZrO2 for the Meerwein-Ponndorf-Verley reaction

[EN] The influence of the crystallographic phase of ZrO2 on its catalytic performance in the MPV reduction of cyclohexanone with propan-2-ol has been systematically investigated by combining accurate synthesis procedures, XRD and HRTEM characterization, kinetic measurements and DFT calculations, and compared to that of Zr-beta zeolite. The higher intrinsic activity of monoclinic zirconia as compared to other ZrO2 phases is not due to a lower activation energy for the rate-determining step, but to an adequate distribution of reactant fragments on the catalyst surface, indicating a structure-activity relationship for this reaction when catalyzed by ZrO2 and also by Zr-beta zeolite. Inexpensive and stable ZrO2 catalysts for the MPV reaction have been obtained by controlling the crystallographic phase of the synthesized material.This work has been supported by the Spanish Government through the "Severo Ochoa Program" (SEV 2012-0267). The Electron Microscopy Service of the UPV is acknowledged for their help in sample characterization. The Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational facilities and technical assistance. F. Gonell is grateful to Ministerio de Educacion, Cultura y Deporte for a PhD grant (AP2010-2748).Gonell-Gómez, F.; Boronat Zaragoza, M.; Corma Canós, A. (2017). Structure-reactivity relationship in isolated Zr sites present in Zr-zeolite and ZrO2 for the Meerwein-Ponndorf-Verley reaction. Catalysis Science & Technology. 7(13):2865-2873. https://doi.org/10.1039/c7cy00567aS2865287371

Hybrid organic-inorganic structured materials as single-site heterogeneous catalysts

Catalyst selectivity is associated with well-defined homogeneous active sites. Transition metal complexes and organocatalysts are highly active and selective in the homogeneous phase, and their heterogenization by incorporating them into inorganic solid materials allows combining their excellent catalytic activity with improved separation, recovering and recycling properties. In this article, we present the structural characteristics and catalytic properties of hybrid organic inorganic materials in which the molecular catalysts are part of the inorganic structure, emphasizing the possibilities of periodic mesoporous hybrid materials and coordination polymers as single-site solid catalysts.We thank Spanish MICINN (Consolider Ingenio 2010-MULTICAT (CSD2009-00050) and MAT2011-29020-C02-01) and Generalitat Valenciana (PROMETEO project 2088/130) for financial support.Díaz Morales, UM.; Boronat Zaragoza, M.; Corma Canós, A. (2012). Hybrid organic-inorganic structured materials as single-site heterogeneous catalysts. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 468(2143):1927-1954. https://doi.org/10.1098/rspa.2012.0066S19271954468214

A new molecular pathway allows the chemoselective reduction of nitroaromatics on non-noble metal catalysts

[EN] At difference with noble metals, the oxophylic character of non-noble metals strongly facilitates the rupture of the N-O bonds in nitrobenzene, yielding nitrosobenzene as primary reaction intermediate. By combining periodic DFT calculations and kinetic studies, a direct pathway involving successive dissociation of N-O bonds followed by two hydrogenation steps, Ph-NO2 -> Ph-NO -> Ph-N -> Ph-NH -> Ph-NH2, has been found as most favorable on Ni catalysts. The rate determining step of the global process is the hydrogen transfer to adsorbed Ph-N intermediate. The catalyst surface becomes partly oxidized during reaction, which favors the vertical adsorption of the nitroaromatic compounds and enhances selectivity, while total surface oxidation leads to catalyst deactivation. It is proposed that both catalytic activity and selectivity of Ni and, possibly, other non-noble metals can be tuned by controlling the degree of oxidation of the metal surface. (C) 2018 Elsevier Inc. All rights reserved. KeywordsThis work has been supported by the Spanish Government through "Severo Ochoa Program" (SEV-2016-0683) and by Generalitat Valenciana through AICO/2017/153 Project. Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational resources and technical support. The authors also thank the Microscopy Service of UPV for kind help on measurements. R. M. acknowledges "La Caixa - Severo Ochoa" International PhD Fellowships (call 2015). L. L. thanks ITQ for providing a PhD scolarship.Millán-Cabrera, R.; Liu, L.; Boronat Zaragoza, M.; Corma Canós, A. (2018). A new molecular pathway allows the chemoselective reduction of nitroaromatics on non-noble metal catalysts. Journal of Catalysis. 364:19-30. https://doi.org/10.1016/j.jcat.2018.05.004193036

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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Effect of the C-alpha substitution on the ketonic decarboxylation of carboxylic acids over m-ZrO2: the role of entropy

[EN] The kinetics of the ketonic decarboxylation of linear and branched carboxylic acids over m-ZrO2 as a catalyst has been investigated. The same apparent activation energy is experimentally determined for the ketonic decarboxylation of both linear pentanoic and branched 2-methyl butanoic acids, while the change in entropy for the rate-determining step differs by nearly 50 kJ mol(-1). These results show that the difference in reactivity between linear and branched acids is due to entropic effects, and is related to the probability of finding the reactant molecules adsorbed and activated in a suitable way on the catalyst surface.The authors thank MINECO (Consolider Ingenio 2010-MULTICAT, CSD2009-00050 and Severo Ochoa program, SEV-2012-0267), Generalitat Valenciana (PROMETEOII/2013/011 Project), and the Spanish National Research Council (CSIC, Es 2010RU0108) for financial support. Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational facilities and technical assistance. A. P., F. G. and B. O.-T. thank MINECO (Juan de la Cierva and FPU Programme) and CSIC (JAE Programme) for their fellowships, respectively. M. R. is grateful to the Generalitat Valenciana for a BEST 2015 fellowship.Oliver-Tomás, B.; Gonell-Gómez, F.; Pulido, A.; Renz, M.; Boronat Zaragoza, M. (2016). Effect of the C-alpha substitution on the ketonic decarboxylation of carboxylic acids over m-ZrO2: the role of entropy. Catalysis Science and Technology. 6(14):5561-5566. https://doi.org/10.1039/c6cy00395hS55615566614Friedel, C. (1858). Ueber s. g. gemischte Acetone. Annalen der Chemie und Pharmacie, 108(1), 122-125. doi:10.1002/jlac.18581080124W. L. Howard , in Encyclopedia of Chemical Technology (Kirk-Othmer), Wiley-Interscience, New York, 4th edn, 1998, vol. 1, pp. 176–194H. Siegel and M.Eggersdorfer, Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, 1990Huber, G. W., Iborra, S., & Corma, A. (2006). Synthesis of Transportation Fuels from Biomass:  Chemistry, Catalysts, and Engineering. Chemical Reviews, 106(9), 4044-4098. doi:10.1021/cr068360dCorma, A., Iborra, S., & Velty, A. (2007). Chemical Routes for the Transformation of Biomass into Chemicals. Chemical Reviews, 107(6), 2411-2502. doi:10.1021/cr050989dChheda, J. N., Huber, G. W., & Dumesic, J. A. (2007). Liquid-Phase Catalytic Processing of Biomass-Derived Oxygenated Hydrocarbons to Fuels and Chemicals. Angewandte Chemie International Edition, 46(38), 7164-7183. doi:10.1002/anie.200604274Renz, M. (2005). Ketonization of Carboxylic Acids by Decarboxylation: Mechanism and Scope. European Journal of Organic Chemistry, 2005(6), 979-988. doi:10.1002/ejoc.200400546Corma, A., Renz, M., & Schaverien, C. (2008). Coupling Fatty Acids by Ketonic Decarboxylation Using Solid Catalysts for the Direct Production of Diesel, Lubricants, and Chemicals. ChemSusChem, 1(8-9), 739-741. doi:10.1002/cssc.200800103Pham, T. N., Sooknoi, T., Crossley, S. P., & Resasco, D. E. (2013). Ketonization of Carboxylic Acids: Mechanisms, Catalysts, and Implications for Biomass Conversion. ACS Catalysis, 3(11), 2456-2473. doi:10.1021/cs400501hSerrano-Ruiz, J. C., Wang, D., & Dumesic, J. A. (2010). Catalytic upgrading of levulinic acid to 5-nonanone. Green Chemistry, 12(4), 574. doi:10.1039/b923907cAlonso, D. M., Bond, J. Q., & Dumesic, J. A. (2010). Catalytic conversion of biomass to biofuels. Green Chemistry, 12(9), 1493. doi:10.1039/c004654jCorma, A., Oliver-Tomas, B., Renz, M., & Simakova, I. L. (2014). Conversion of levulinic acid derived valeric acid into a liquid transportation fuel of the kerosene type. Journal of Molecular Catalysis A: Chemical, 388-389, 116-122. doi:10.1016/j.molcata.2013.11.015Rajadurai, S. (1994). Pathways for Carboxylic Acid Decomposition on Transition Metal Oxides. Catalysis Reviews, 36(3), 385-403. doi:10.1080/01614949408009466Gliński, M., Kijeński, J., & Jakubowski, A. (1995). Ketones from monocarboxylic acids: Catalytic ketonization over oxide systems. Applied Catalysis A: General, 128(2), 209-217. doi:10.1016/0926-860x(95)00082-8Pestman, R., Koster, R. M., van Duijne, A., Pieterse, J. A. Z., & Ponec, V. (1997). Reactions of Carboxylic Acids on Oxides. Journal of Catalysis, 168(2), 265-272. doi:10.1006/jcat.1997.1624Parida, K., & Mishra, H. K. (1999). Catalytic ketonisation of acetic acid over modified zirconia. Journal of Molecular Catalysis A: Chemical, 139(1), 73-80. doi:10.1016/s1381-1169(98)00184-8Hendren, T. S., & Dooley, K. M. (2003). Kinetics of catalyzed acid/acid and acid/aldehyde condensation reactions to non-symmetric ketones. Catalysis Today, 85(2-4), 333-351. doi:10.1016/s0920-5861(03)00399-7Martinez, R. (2004). Ketonization of acetic acid on titania-functionalized silica monoliths. Journal of Catalysis, 222(2), 404-409. doi:10.1016/j.jcat.2003.12.002Pulido, A., Oliver-Tomas, B., Renz, M., Boronat, M., & Corma, A. (2012). Ketonic Decarboxylation Reaction Mechanism: A Combined Experimental and DFT Study. ChemSusChem, 6(1), 141-151. doi:10.1002/cssc.201200419Ignatchenko, A. V., DeRaddo, J. S., Marino, V. J., & Mercado, A. (2015). Cross-selectivity in the catalytic ketonization of carboxylic acids. Applied Catalysis A: General, 498, 10-24. doi:10.1016/j.apcata.2015.03.017Ignatchenko, A. V., & Kozliak, E. I. (2012). Distinguishing Enolic and Carbonyl Components in the Mechanism of Carboxylic Acid Ketonization on Monoclinic Zirconia. ACS Catalysis, 2(8), 1555-1562. doi:10.1021/cs3002989Ignatchenko, A. V. (2011). Density Functional Theory Study of Carboxylic Acids Adsorption and Enolization on Monoclinic Zirconia Surfaces. The Journal of Physical Chemistry C, 115(32), 16012-16018. doi:10.1021/jp203381hJackson, M. A., & Cermak, S. C. (2012). Cross ketonization of Cuphea sp. oil with acetic acid over a composite oxide of Fe, Ce, and Al. Applied Catalysis A: General, 431-432, 157-163. doi:10.1016/j.apcata.2012.04.034Plint, N. ., Coville, N. ., Lack, D., Nattrass, G. ., & Vallay, T. (2001). The catalysed synthesis of symmetrical ketones from alcohols. Journal of Molecular Catalysis A: Chemical, 165(1-2), 275-281. doi:10.1016/s1381-1169(00)00445-3Randery, S. (2002). Cerium oxide-based catalysts for production of ketones by acid condensation. Applied Catalysis A: General, 226(1-2), 265-280. doi:10.1016/s0926-860x(01)00912-

Identification of Distinct Copper Species in Cu-CHA Samples Using NO as Probe Molecule. A Combined IR Spectroscopic and DFT Study

[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. 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Enhanced Stability of Cu Clusters of Low Atomicity against Oxidation. Effect on the Catalytic Redox Process

[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.7b00778S356035687