Single-Atom Catalysis in Organic Synthesis

Single-atom catalysts hold the potential to significantly impact the chemical sector, pushing the boundaries of catalysis in new, uncharted directions. These materials, featuring isolated metal species ligated on solid supports, can exist in many coordination environments, all of which have shown important functions in specific transformations. Their emergence has also provided exciting opportunities for mimicking metalloenzymes and bridging the gap between homogeneous and heterogeneous catalysis. This review outlines the impressive progress made in recent years regarding the use of single-atom catalysts in organic synthesis. We also illustrate potential knowledge gaps in the search for more sustainable, earth-abundant single-atom catalysts for synthetic applications

Structural Effects of Metal Single-Atom Catalysts for Enhanced Photocatalytic Degradation of Gemfibrozil

The development of efficient catalysts is a highly necessary but challenging task within the field of environmental water remediation. Single-atom catalysts are promising nanomaterials within this respect, but in-depth studies encompassing this class of catalysts remain elusive. In this work, we systematically study the degradation of gemfibrozil, a persistent pollutant, on a series of carbon nitride photocatalysts, investigating both the effect of (i) catalyst textural properties and (ii) metal single atoms on the contaminant degradation. Tests in the absence of the catalyst result in negligible degradation rates, confirming the stability of the contaminant when dispersed in water. Then, photocatalytic tests at optimal pH, solvent, and wavelength reveal a correlation between the support surface area and the degradation. This points to the role of carbon nitride surface nanostructure on gemfibrozil degradation. In particular, the use of silver on mesoporous carbon nitride single-atom catalyst (Ag@mpgC(3)N(4)) leads to an unprecedented degradation of gemfibrozil (>90% within 60 min). The possible degradation intermediates and products were identified by mass spectrometry and were inert by cytotoxicity evaluation. We anticipate that, with further refinement and customization, the carbon nitride catalysts reported herein may find broad applications for light-driven degradation of other contaminants of emerging concern

Ligand–metal charge transfer induced via adjustment of textural properties controls the performance of single-atom catalysts during photocatalytic degradation

Because of their peculiar nitrogen-rich structure, carbon nitrides are convenient polydentate ligands for designing single atom-dispersed photocatalysts. However, the relation between catalysts’ textural properties and their photophysical–photocatalytic properties is rarely elaborated. Herein, we report the preparation and characterization of a series of single-atom heterogeneous catalysts featuring highly dispersed Ag and Cu species on mesoporous graphitic C3N4. We show that adjustment of materials textural properties and therefore metal single-atom coordination mode enables ligand-to-metal charge transfer (LMCT) or ligand-to-metal-to-ligand charge transfer (LMLCT), properties that were long speculated in single-atom catalysis but never observed. We employ the developed materials in the degradation of organic pollutants under irradiation with visible light. Kinetic investigations under flow conditions show that single atoms of Ag and Cu decrease the number of toxic organic fragmentation products while leading to a higher selectivity toward full degradation. The results correlate with the selected mode of charge transfer in the designed photocatalysts and provide a new understanding of how the local environment of a single-atom catalyst affects the surface structure and reactivity. The concepts can be exploited further to rationally design and optimize other single-atom materials

Nanostructured Carbon Nitride for Continuous-Flow Trifluoromethylation of (Hetero)arenes

Efficient catalytic methods for the trifluoromethy-lation of (hetero)arenes are of particular importance in organic and pharmaceutical manufacturing. However, many existing protocols rely on toxic reagents and expensive or sterically hindered homogeneous catalysts. One promising alternative to conduct this transformation involves the use of carbon nitride, a non-toxic photocatalyst prepared from inexpensive precursors. Nonetheless, there is still little understanding regarding the interplay between physicochemical features of this photocatalyst and the correspond-ing effects on the reaction rate. In this work, we elucidate the role of carbon nitride nanostructuring on the catalytic performance, understanding the effect of surface area and band gap tuning via metal insertion. Our findings provide new insights into the structure-function relationships of the catalyst, which we exploit to design a continuous-flow process that maximizes catalyst-light interaction, facilitates catalyst reusability, and enables intensified reaction scale-up. This is particularly significant given that photocatalyzed batch protocols often face challenges during industrial exploitation. Finally, we extrapolate the rapid and simplified continuous-flow method to the synthesis of a variety of functionalized heteroaromatics, which have numerous applications in the pharmaceutical and fine chemical industries

Trabajo profesional y conflicto trabajo-escuela en estudiantes-trabajadores: El papel mediador de distanciamiento psicológico del trabajo

In recent years there Portuguese higher education institutions have been aiming to attract more people to the educational system that are either in the labor market by offering evening and weekend graduate academic programs. Blending work and school is a demanding task and, so far, at the country level this phenomenon has received relatively little empirical attention. The purpose of the study is to build on existing work-to-school conflict literature and to explore a possible relationship between professional work load on work-to-school conflicts among working students enrolled in a master program. Moreover we test the role of psychological detachment from work as mediator in this process. This model was tested, through path analysis, using 152 working students, 88 women and 64 men, enrolled as fulltime students in evening and weekend master programs.. The model showed an adequate fit to the data, suggesting that the influence of professional work load on work-to-school conflict is fully mediated by psychological detachment from work. These findings unveil a new perspective on working students enrolled in postgraduate school, pointing out the importance of psychological detachment from work to a better understand the impact of blending work and school. Contributions to the work-school literature, future research directions, and limitations of the study are discussed. En los últimos años, las instituciones de enseñanza superior portuguesas han intentado atraer a más personas al sistema educativo que se encuentran en el mercado laboral ofreciendo programas académicos de posgrado nocturnos y de fin de semana. La combinación del trabajo y la escuela es una tarea exigente y, hasta ahora, a nivel de país este fenómeno ha recibido relativamente poca atención empírica. El propósito del estudio es basarse en la literatura sobre conflictos de trabajo a escuela existentes y explorar una posible relación entre la carga de trabajo profesional en los conflictos entre el trabajo y la escuela entre los estudiantes que trabajan matriculados en un programa de maestría. Además, probamos el papel del desapego psicológico del trabajo como mediador en este proceso. Este modelo fue probado, a través de análisis de trayectoria, utilizando 152 estudiantes de trabajo, 88 mujeres y 64 hombres, matriculados como estudiantes de tiempo completo en programas de posgrado de tarde y fin de semana. El modelo mostró un ajuste adecuado a los datos, sugiriendo que la influencia de la carga de trabajo profesional en el conflicto entre el trabajo y la escuela está plenamente mediado por el desapego psicológico del trabajo. Estos resultados revelan una nueva perspectiva sobre los estudiantes que trabajan y que frecuentan la escuela de posgrado, señalando la importancia del desapego psicológico del trabajo para comprender mejor el impacto de la mezcla de trabajo y la escuela. Se discuten las contribuciones a la literatura de la escuela de trabajo, las direcciones futuras de la investigación y las limitaciones del estudio

Ceria-zirconia particles wrapped in a 2D carbon envelope: improved low-temperature oxygen transfer and oxidation activity

Engineering the interface between different compo-nents of heterogeneous catalysts at nanometer level canradically alter their performances.This is particularly true forceria-based catalysts where the interactions are critical forobtaining materials with enhanced properties.Here we showthat mechanical contact achieved by high-energy milling ofCeO2–ZrO2powders and carbon soot results in the formationof acore of oxide particles wrapped in athin carbon envelope.This 2D nanoscale carbon arrangement greatly increases thenumber and quality of contact points between the oxide andcarbon. Consequently,the temperatures of activation andtransfer of the oxygen in ceria are shifted to exceptionally lowtemperatures and the soot combustion rate is boosted. Thestudy confirms the importance of the redox behavior of ceria-zirconia particles in the mechanism of soot oxidation andshows that the organization of contact points at the nanoscalecan significantly modify the reactivity resulting in unexpectedproperties and functionalities.Postprint (published version

Enhanced flow synthesis of small molecules by in-line integration of sequential catalysis and benchtop twin-column continuous chromatography

We report an improved approach for the integration of flow synthesis and continuous chromatography, for applications in the end-to-end preparation of pharmaceutically-relevant small molecules. It involves the combination of sequential microreactors and twin-column counter-current chromatography based on the often-used C18 columns. The column loading method ensures that the product breaking through a fully loaded first column is loaded onto the second one, avoiding waste of precious material and technological complexity associated with the use of four-to-six columns typical of simulated moving bed chromatography. The system was applied to synthesize biphenyl via Suzuki–Miyaura reaction, and was also demonstrated for other structurally-different compounds. Compared to the discontinuous and other traditional approaches, our method leads to higher isolated yields (ca. +60%), higher productivity (ca. +30%), and reduced solvent consumption (ca. −80%). A circularity and life-cycle analysis was also conducted to demonstrate the environmental benefits of the flow process

The acid-base and redox reactivity of CeO2 nanoparticles: Influence of the Hubbard U term in DFT plus U studies

[EN] 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 O-2 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. We thank Konstantin Neyman for providing the Ce21O42 nanoparticle model.Boronat Zaragoza, M.; López Auséns, JT.; Corma Canós, A. (2016). The acid-base and redox reactivity of CeO2 nanoparticles: Influence of the Hubbard U term in DFT plus U studies. Surface Science. 648:212-219. https://doi.org/10.1016/j.susc.2015.10.047S21221964