Heterogeneous Metal Catalysts: From Single Atoms to Nanoclusters and Nanoparticles

Tesis por compendioLas especies de metal con diferentes tamaños (átomos individuales, nanocristales y nanopartículas) muestran un comportamiento catalítico diferente para diversas reacciones catalíticas heterogéneas. Se ha demostrado en la bibliografía que muchos factores que incluyen el tamaño de partícula, la forma, la composición química, la interacción metal-soporte, la interacción metal-reactivo / disolvente, pueden tener influencias significativas sobre las propiedades catalíticas de los catalizadores metálicos. Los desarrollos recientes de metodologías de síntesis bien controladas y herramientas de caracterización avanzada permiten correlacionar las relaciones a nivel molecular. En esta tesis, he llevado a cabo estudios sobre catalizadores metálicos desde átomos individuales hasta nanoclusters y nanopartículas. Al desarrollar nuevas metodologías de síntesis, el tamaño de las especies metálicas puede modularse y usarse como catalizadores modelo para estudiar el efecto del tamaño sobre el comportamiento catalítico de los catalizadores metálicos para la oxidación del CO, la hidrogenación selectiva, la oxidación selectiva y la fotocatálisis. Se ha encontrado que, los átomos metálicos dispersados por separado y los grupos subnanométricos de metal pueden aglomerarse en nanoclusters o nanopartículas más grandes en condiciones de reacción. Para mejorar la estabilidad de los catalizadores subnanométricos de metal, he desarrollado una nueva estrategia para la generación de átomos individuales y clusters en zeolitas. Esas especies subnanométricas de metales son estables en tratamientos de oxidación-reducción a 550 oC. Siguiendo esta nueva metodología de síntesis, este nuevo tipo de materiales puede servir como catalizador modelo para estudiar la evolución de especies subnanométricas de metales en condiciones de reacción. La transformación estructural de las especies subnanométricas de Pt ha sido estudiada mediante microscopía electrónica de transmisión in situ. Se ha demostrado que el tamaño de las especies de Pt está fuertemente relacionado con las condiciones de reacción, que proporcionan importantes conocimientos para comprender el comportamiento de los catalizadores de metales subnanométricos en condiciones de reacción. En la otra línea de investigación para catalizadores de metales no nobles, he desarrollado varias estrategias generales para obtener catalizadores de metales no nobles, ya sea soportados sobre óxidos metálicos o protegidos por capas delgadas de carbono. Estos materiales muestran un rendimiento excelente para varias reacciones importantes, como la hidrogenación quimioselectiva de nitroarenos, incluso cuando se comparan con los catalizadores de metales nobles convencionales. En algunos casos, los catalizadores de metales no nobles pueden incluso alcanzar selectividades para productos inviables que no ha sido posible conseguir en catalizadores de metales nobles convencionales, que es causado por la diferente ruta de reacción en catalizadores de metales no nobles. Sin embargo, la espectroscopía fotoelectrónica de rayos X a presión ambiente ha revelado que la irradiación de la luz puede modular la selectividad a los alcoholes y los hidrocarburos C2 +, lo que abre una nueva posibilidad para ajustar el comportamiento catalítico de los catalizadores metálicos. Con base en los trabajos anteriores de diferentes aspectos relacionados con catalizadores metálicos heterogéneos, las perspectivas sobre las direcciones futuras hacia una mejor comprensión del comportamiento catalítico de diferentes entidades metálicas (átomos individuales, nanoagrupamientos y nanopartículas) de una manera unificadora también se han dado en esta tesis.Les espècies metàl·liques de diferents dimensions (àtoms individuals, nanoclusters i nanopartícules) mostren diferents comportaments catalítics per a diverses reaccions catalítiques heterogènies. S'ha demostrat a la literatura que, molts factors que inclouen la mida de la partícula, la forma, la composició química, la interacció amb el suport metàl·lic, la reacció metàl·lica i la interacció amb dissolvents poden tenir influències significatives sobre les propietats catalítiques dels catalitzadors metàl·lics. Els desenvolupaments recents de metodologies de síntesi ben controlades i eines de caracterització avançada permeten relacionar les relacions a nivell molecular. En aquesta tesi, he realitzat estudis sobre catalitzadors metàl·lics d'àtoms únics a nanoclústers i nanopartícules. Mitjançant el desenvolupament de noves metodologies de síntesi, la mida de les espècies metàl·liques es pot modular i utilitzar com a catalitzadors model per estudiar l'efecte de mida sobre el comportament catalític dels catalitzadors metàl·lics per a l'oxidació de CO, hidrogenació selectiva, oxidació selectiva i fotocatàlisi. S'ha trobat que, els àtoms metàl·lics dispersos individualment i els clústers metàl·lics subnanomètrics poden aglomerar-se en nanoclústeres o nanopartícules més grans en condicions de reacció. Per millorar l'estabilitat dels catalitzadors subnanomètrics de metall, he desenvolupat una nova estratègia per a la generació d'àtoms i racimos en zeolites. Aquestes espècies metàl·liques subnanométricas són estables en tractaments de reducció d'oxidació a 550 oC. Després d'aquesta nova metodologia de síntesi, aquest nou tipus de materials poden servir com a model de catalitzador per estudiar l'evolució de les espècies metàl·liques subnanométricas en condicions de reacció. La transformació estructural de l'espècie Pn subnanométrica ha estat estudiada per microscòpia electrònica de transmissió in situ. S'ha demostrat que la mida de les espècies de Pt està fortament relacionada amb les condicions de reacció, que proporcionen idees importants per comprendre el comportament dels catalitzadors de subnanometria en condicions de reacció. En l'altra línia de recerca dels catalitzadors de metalls no nobles, he desenvolupat diverses estratègies generals per obtenir catalizadors de metalls no nobles recolzats en òxids metàl·lics o protegits per capes de carboni primes. Aquests materials presenten un excel·lent rendiment per a diverses reaccions importants, com la hidrogenació quimioelectiva de nitroarenes, fins i tot quan es comparen amb els catalitzadors convencionals de metall noble. En alguns casos, els catalitzadors de metalls no nobles poden fins i tot aconseguir selectivitats a productes no factibles que no s'han pogut assolir en catalitzadors de metall noble convencionals, que es deuen a la via de reacció diferent en catalitzadors de metalls no nobles. No obstant això, s'ha observat una espectroscòpia de fotoelèctria de raigs X amb pressió d'atmosfera que la irradiació lleugera pot modular la selectivitat als alcohols i hidrocarburs C2 +, la qual cosa obre una nova possibilitat per sintonitzar el comportament catalític dels catalitzadors metàl·lics. A partir d'aquests treballs de diferents aspectes relacionats amb els catalitzadors metàl·lics heterogenis, també s'ha donat en aquesta tesi perspectives sobre les futures orientacions cap a una millor comprensió del comportament catalític de diferents entitats metàl·liques (àtoms individuals, nanoclústers i nanopartícules).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, 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 to correlate the relationships at molecular level. In this thesis, I have carried out studies on metal catalysts from single atoms to nanoclusters and nanoparticles. By developing new synthesis methodologies, the size of metal species can be modulated and used as model catalysts to study the size effect on the catalytic behavior of metal catalysts for CO oxidation, selective hydrogenation, selective oxidation and photocatalysis. It has been found that, singly dispersed metal atoms and subnanometric metal clusters may agglomerate into larger nanoclusters or nanoparticles under reaction conditions. To improve the stability of subnanometric metal catalysts, I have developed a new strategy for the generation of single atoms and clusters in zeolites. Those subnanometric metal species are stable in oxidation-reduction treatments at 550 oC. Following this new synthesis methodology, this new type of materials can serve as model catalyst to study the evolution of subnanometric metal species under reaction conditions. The structural transformation of subnanometric Pt species has been studied by in situ transmission electron microscopy. It has been shown that the size of Pt species is strongly related with the reaction conditions, which provide important insights for understanding the behavior of subnanometric metal catalysts under reaction conditions. In the other research line for non-noble metal catalysts, I have developed several general strategies to obtain non-noble metal catalysts either supported on metal oxides or protected by thin carbon layers. These materials show excellent performance for several important reactions, such as chemoselective hydrogenation of nitroarenes, even when compared with conventional noble metal catalysts. In some cases, non-noble metal catalysts can even achieve selectivities to unfeasible products which has not been possible to achieve on conventional noble metal catalysts, which is caused by the different reaction pathway on non-noble metal catalysts. Nevertheless, it has been revealed by ambient-pressure X-ray photoelectron spectroscopy that light irradiation can modulate the selectivity to alcohols and C2+ hydrocarbons, which opens a new possibility for tuning the catalytic behavior of metal catalysts. Based on the above works from different aspects related with heterogeneous metal catalysts, perspectives on the future directions towards better understanding on the catalytic behavior of different metal entities (single atoms, nanoclusters and nanoparticles) in a unifying manner have also been given in this thesis.Liu, L. (2018). Heterogeneous Metal Catalysts: From Single Atoms to Nanoclusters and Nanoparticles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113169TESISCompendi

Controllable synthesis of metal nanoparticles for catalytic applications

[EN] In this thesis, I have discussed the synthesis of Cu nanoparticles and their applications in C-N coupling reactions. I find that Cu nanoparticles will decompose into Cu clusters and Cu clusters are the real active species. In the second part, I show sorne work on preparation of highly stable ultra-small Pt nanoparticles incorporated into MCM-22[ES] Se ha discutido la síntesis de nanopartículas (NPs) de Cu y y sus aplicaciones en reacciones catalíticas de "coupling" C-N, confirmándose que las NPs descomponen en clústers que actúan como las especies activas del proceso. En una segunda parte, se ha mostrado la preparación de NPs estables de Pt incorporadas en la zeolita MCM-22Liu, L. (2014). Controllable synthesis of metal nanoparticles for catalytic applications. http://hdl.handle.net/10251/47434Archivo delegad

Confining isolated atoms and clusters in crystalline porous materials for catalysis

[EN] Structure-reactivity relationships for nanoparticle-based catalysts have been greatly influenced by the study of catalytic materials with either supported isolated metal atoms or metal clusters comprising a few atoms. The stability of these metal species is a key challenge because they can sinter into large nanoparticles under harsh reaction conditions. However, stability can be achieved by confining the nanoparticles in crystalline porous materials (such as zeolites and metal-organic frameworks). More importantly, the interaction between the metal species and the porous framework may modulate the geometric and electronic structures of the subnanometric metal species, especially for metal clusters. This confinement effect can induce shape-selective catalysis or different chemoselectivity from that of metal atoms supported on open-structure solid carriers. In this Review, we discuss the structural features, synthesis methodologies, characterization techniques and catalytic applications of subnanometric species confined in zeolites and metal-organic frameworks. We make a critical comparison between confined and non-confined isolated atoms and metal clusters, and provide future perspectives for the field.We are grateful for financial support from the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish Government through the Severo Ochoa Program (SEV-2016-0683).Liu, L.; Corma Canós, A. (2021). Confining isolated atoms and clusters in crystalline porous materials for catalysis. Nature Reviews Materials. 6(3):244-263. https://doi.org/10.1038/s41578-020-00250-32442636

Isolated metal atoms and clusters for alkane activation: translating knowledge from enzymatic and homogeneous to heterogeneous systems

[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.2021.04.001S234723847

Modulating the catalytic behavior of non-noble metal nanoparticles by inter-particle interaction for chemoselective hydrogenation of nitroarenes into corresponding azoxy or azo compounds

[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.2018.11.011S31232336

Nanolayered Co-Mo-S Catalysts for the Chemoselective Hydrogenation of Nitroarenes

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.7b00170S269827087

Influencing factors of resident satisfaction in smart community services： An empirical study in Chengdu

Smart communities have shown great advantages in China\u27s pandemic control, but also exposed the shortcomings that some smart community services (SCS) are out of touch with residents\u27 needs in the post-pandemic era. Therefore, This study aims to explore those SCSs were needed to promote the sustainable development of smart communities. Based on the expectation disconfirmation theory and the modified ASCI model, this study establishes a smart community service resident satisfaction model and analyzes it with Amos structural equation model. The study results are as follows: (1) SCS outcome, ICT infrastructure, and SCS delivery all have a positive influence on resident satisfaction and their performances decrease in turn. (2) some of the factors that drive resident satisfaction most, such as Smart Property Service and Public Facility, have a lower rating. (3) residents are more concerned about the cost (including financial and emotional costs) than the quality of the SCSs. (4) Most residents\u27 expectations of SCS are irrational and that’s why it does not have a significant impact on satisfaction. (5) Resident Satisfaction is an important factor in enhancing Resident Confidence in SCS and promoting Resident Participation in improving SCS. This enlightens us that improving resident satisfaction is one of the effective ways to promote the sustainable development of Smart Community and continuously enhance the emergency response capabilities of grassroots communities in the post-pandemic era

Generation of gold nanoclusters encapsulated in an MCM-22 zeolite for the aerobic oxidation of cyclohexane

[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/c8cc07185cS160716105511Claus, P. (2005). Heterogeneously catalysed hydrogenation using gold catalysts. Applied Catalysis A: General, 291(1-2), 222-229. doi:10.1016/j.apcata.2004.12.048Hashmi, A. S. K., & Hutchings, G. J. (2006). Gold Catalysis. Angewandte Chemie International Edition, 45(47), 7896-7936. doi:10.1002/anie.200602454Liu, L., & Corma, A. (2018). Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles. Chemical Reviews, 118(10), 4981-5079. doi:10.1021/acs.chemrev.7b00776Valden, M. (1998). Onset of Catalytic Activity of Gold Clusters on Titania with the Appearance of Nonmetallic Properties. Science, 281(5383), 1647-1650. doi:10.1126/science.281.5383.1647Hvolbæk, B., Janssens, T. V. W., Clausen, B. S., Falsig, H., Christensen, C. H., & Nørskov, J. K. (2007). Catalytic activity of Au nanoparticles. Nano Today, 2(4), 14-18. doi:10.1016/s1748-0132(07)70113-5Oliver-Meseguer, J., Cabrero-Antonino, J. R., Dominguez, I., Leyva-Perez, A., & Corma, A. (2012). Small Gold Clusters Formed in Solution Give Reaction Turnover Numbers of 107 at Room Temperature. Science, 338(6113), 1452-1455. doi:10.1126/science.1227813Corma, A., Concepción, P., Boronat, M., Sabater, M. J., Navas, J., Yacaman, M. J., … Mayoral, A. (2013). Exceptional oxidation activity with size-controlled supported gold clusters of low atomicity. Nature Chemistry, 5(9), 775-781. doi:10.1038/nchem.1721Boronat, M., Leyva-Pérez, A., & Corma, A. (2013). Theoretical and Experimental Insights into the Origin of the Catalytic Activity of Subnanometric Gold Clusters: Attempts to Predict Reactivity with Clusters and Nanoparticles of Gold. Accounts of Chemical Research, 47(3), 834-844. doi:10.1021/ar400068wYamazoe, S., Koyasu, K., & Tsukuda, T. (2013). Nonscalable Oxidation Catalysis of Gold Clusters. Accounts of Chemical Research, 47(3), 816-824. doi:10.1021/ar400209aBore, M. T., Pham, H. N., Switzer, E. E., Ward, T. L., Fukuoka, A., & Datye, A. K. (2005). The Role of Pore Size and Structure on the Thermal Stability of Gold Nanoparticles within Mesoporous Silica. The Journal of Physical Chemistry B, 109(7), 2873-2880. doi:10.1021/jp045917pOtto, T., Zones, S. I., & Iglesia, E. (2016). Challenges and strategies in the encapsulation and stabilization of monodisperse Au clusters within zeolites. Journal of Catalysis, 339, 195-208. doi:10.1016/j.jcat.2016.04.015Liu, L., Díaz, U., Arenal, R., Agostini, G., Concepción, P., & Corma, A. (2016). Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D. Nature Materials, 16(1), 132-138. doi:10.1038/nmat4757Liu, L., Zakharov, D. N., Arenal, R., Concepcion, P., Stach, E. A., & Corma, A. (2018). Evolution and stabilization of subnanometric metal species in confined space by in situ TEM. Nature Communications, 9(1). doi:10.1038/s41467-018-03012-6Xue, Y., Li, X., Li, H., & Zhang, W. (2014). Quantifying thiol–gold interactions towards the efficient strength control. Nature Communications, 5(1). doi:10.1038/ncomms5348Pensa, E., Cortés, E., Corthey, G., Carro, P., Vericat, C., Fonticelli, M. H., … Salvarezza, R. C. (2012). The Chemistry of the Sulfur–Gold Interface: In Search of a Unified Model. Accounts of Chemical Research, 45(8), 1183-1192. doi:10.1021/ar200260pShivhare, A., Chevrier, D. M., Purves, R. W., & Scott, R. W. J. (2013). Following the Thermal Activation of Au25(SR)18 Clusters for Catalysis by X-ray Absorption Spectroscopy. The Journal of Physical Chemistry C, 117(39), 20007-20016. doi:10.1021/jp4063687Miller, J. T., Kropf, A. J., Zha, Y., Regalbuto, J. R., Delannoy, L., Louis, C., … van Bokhoven, J. A. (2006). The effect of gold particle size on AuAu bond length and reactivity toward oxygen in supported catalysts. Journal of Catalysis, 240(2), 222-234. doi:10.1016/j.jcat.2006.04.004Zhu, M., Aikens, C. M., Hollander, F. J., Schatz, G. C., & Jin, R. (2008). Correlating the Crystal Structure of A Thiol-Protected Au25Cluster and Optical Properties. Journal of the American Chemical Society, 130(18), 5883-5885. doi:10.1021/ja801173rI. Hermans , Liquid Phase Aerobic Oxidation Catalysis-Industrial Applications and Academic Perspectives , ed. S. Stahl and P. Alsters , 2015Hereijgers, B. P. C., & Weckhuysen, B. M. (2010). Aerobic oxidation of cyclohexane by gold-based catalysts: New mechanistic insight by thorough product analysis. Journal of Catalysis, 270(1), 16-25. doi:10.1016/j.jcat.2009.12.003Hermans, I., Jacobs, P. A., & Peeters, J. (2006). To the Core of Autocatalysis in Cyclohexane Autoxidation. Chemistry - A European Journal, 12(16), 4229-4240. doi:10.1002/chem.200600189Conte, M., Liu, X., Murphy, D. M., Whiston, K., & Hutchings, G. J. (2012). Cyclohexane oxidation using Au/MgO: an investigation of the reaction mechanism. Physical Chemistry Chemical Physics, 14(47), 16279. doi:10.1039/c2cp43363jQian, L., Wang, Z., Beletskiy, E. V., Liu, J., dos Santos, H. J., Li, T., … Kung, H. H. (2017). Stable and solubilized active Au atom clusters for selective epoxidation of cis-cyclooctene with molecular oxygen. Nature Communications, 8(1). doi:10.1038/ncomms1488