Shape effects of ceria nanoparticles on the water-gas shift performance of cuox /ceo2 catalysts

T1EDK-00094 UIDB/EQU/50020/2020 UIDB/00511/2020 CEECINST/00102/2018 UIDB/50006/2020 UIDP/50006/2020 DL 57/2017The copper–ceria (CuOx /CeO2 ) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx /CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R > P > C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+ ) through the Cu2+ /Cu+ and Ce4+ /Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx /CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350◦ C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance.publishersversionpublishe

The byzantine masculinity at war: An approach on the manliness of the army in the middle byzantine era [La masculinidad bizantina en la guerra: Una aproximación a la virilidad del ejército en la época medio bizantina]

As a social phenomenon war affects soldiers and civilians, men and women. The present contribution aims to examine various conceptions of masculinities within a military context during the Middle Byzantine Era. The identity of the Byzantine soldier is tightly connected with a specific type of masculinity that is derived from the Roman past and the Christian religion. The evolution of the military system during the middle era creates new types of soldiers that are called to oppose the powerful enemies of the Empire. Victorious engagements, typically result in moral principles that are in contrast with those found while in state of defeat. Thus, in this study, special attention will be given to the soldiers’ identity and behaviour during their captivity. It is interesting to explore how that transitional situation affects the characteristics of the Middle Byzantine combatant masculinity. © 2020 Universidad de Chile. All rights reserved

Facet-dependent reactivity of Fe2O3/CeO2 nanocomposites: Effect of ceria morphology on CO oxidation

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at -196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species. © 2019 by the authors. Licensee MDPI, Basel, Switzerland

Hydrothermal synthesis of ZnO–doped ceria nanorods: Effect of zno content on the redox properties and the co oxidation performance

The rational design of highly efficient, noble metal–free metal oxides is one of the main research priorities in the area of catalysis. To this end, the fine tuning of ceria–based mixed oxides by means of aliovalent metal doping has currently received particular attention due to the peculiar metal–ceria synergistic interactions. Herein, we report on the synthesis, characterization and catalytic evaluation of ZnO–doped ceria nanorods (NR). In particular, a series of bare CeO2 and ZnO oxides along with CeO2/ZnO mixed oxides of different Zn/Ce atomic ratios (0.2, 0.4, 0.6) were prepared by the hydrothermal method. All prepared samples were characterized by X–ray diffraction (XRD), N2 physisorption, temperature–programmed reduction (TPR), scanning electron microscopy with energy dispersive X–ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The CO oxidation reaction was employed as a probe reaction to gain insight into structure–property relationships. The results clearly showed the superiority of mixed oxides as compared to bare ones, which could be ascribed to a synergistic ZnO–CeO2 interaction towards an improved reducibility and oxygen mobility. A close correlation between the catalytic activity and oxygen storage capacity (OSC) was disclosed. Comparison with relevant literature studies verifies the role of OSC as a key activity descriptor for reactions following a redox–type mechanism. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Effect of the preparation method on the physicochemical properties and the CO oxidation performance of nanostructured CeO2/TiO2 oxides

Ceria-based mixed oxides have been widely studied in catalysis due to their unique surface and redox properties, with implications in numerous energy-and environmental-related applications. In this regard, the rational design of ceria-based composites by means of advanced synthetic routes has gained particular attention. In the present work, ceria-titania composites were synthesized by four different methods (precipitation, hydrothermal in one and two steps, Stober) and their effect on the physicochemical characteristics and the CO oxidation performance was investigated. A thorough characterization study, including N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM) and H2 temperature-programmed reduction (H2-TPR) was performed. Ceria-titania samples prepared by the Stober method, exhibited the optimum CO oxidation performance, followed by samples prepared by the hydrothermal method in one step, whereas the precipitation method led to almost inactive oxides. CeO2/TiO2 samples synthesized by the Stober method display a rod-like morphology of ceria nanoparticles with a uniform distribution of TiO2, leading to enhanced reducibility and oxygen storage capacity (OSC). A linear relationship was disclosed among the catalytic performance of the samples prepared by different methods and the abundance of reducible oxygen species. © 2020 by the authors

Fabrication of highly active and stable Ni/CeO2-nanorods wash-coated on ceramic NZP structured catalysts for scaled-up CO2 methanation

The production of synthetic natural gas from CO2 methanation using green H2 produced via water electrolysis is a promising pathway regarding both the curtailment of excess power by variable renewables and the mitigation of CO2 emissions. Several catalytic systems have been employed for thermocatalytic CO2 methanation in lab-scale, with Ni-based catalysts being amongst the most cost-effective and active materials. In this regard, we have recently demonstrated the remarkable low-temperature CO2 methanation activity of a nickel catalyst supported on ceria nanorods, ascribed to the augmented metal-support synergy. Herein, we report on a scaled-up process of CO2 methanation, involving; i) fabrication of a highly porous NZP-type ceramic substrate of Ba1+xZr4P6–2xSi2xO24 in the form of extruded pellets, ii) wash-coating of Ni/CeO2-nanorods catalyst on NZP pellets, iii) design and testing of scaled-up experiments under a scaling factor of 80:1 and 65:1 in terms of mass and volume of catalysts compared to lab-scale experiments, respectively. The as-synthesized catalyst exhibited remarkable performance under variable reaction conditions and stable behavior after 75 h. Remarkably, the structured catalyst attained a methane formation rate of 277 NL gNi−1 h−1, being higher to numerous values reported in relevant works. Equally importantly, it was disclosed that increased values of space velocity led to high temperature gradient in the catalytic bed, thereby favoring the generation of CO. Intriguingly, the morphological and structural characteristics of the used catalyst remained unaltered even after various on/off reaction cycles and the stability test, which is a promising finding toward scaling-up the process at higher technology readiness levels using real feed streams. © 2023 The Author

Pillages, tributs, captifs

La prédation est une réalité incontournable des sociétés du haut Moyen Âge. Que l’on pense au sac de Rome par les Wisigoths en 410, au récit du vase de Soissons, aux déprédations vikings des IXe et Xe siècles, ou encore aux razzias incessantes de la guerre féodale, l’histoire de ce temps est traversée de pillages, de captures, de prélèvements de tributs effectués par la force. Associées pendant longtemps à une conception négative du Moyen Âge, ces pratiques ont peu intéressé les chercheurs. Tout au plus s’y est-on parfois penché de manière biaisée, par exemple en étudiant les conséquences des déprédations vikings, hongroises ou sarrasines sur l’Occident chrétien. Cela revenait implicitement à enfermer certaines sociétés, comme les Scandinaves, dans leur dimension prédatrice, alors que l’Occident chrétien ne pouvait être pensé, selon le contexte, que dans le rôle de victime ou de conquérant. Considérée depuis quelques décennies dans une autre perspective, la prédation est désormais envisagée comme un phénomène économique, politique, social et culturel. Abordant les questions aussi diverses que les formes de partage du butin, la place de la prédation dans la circulation des richesses, l’insertion des captifs de guerre dans les économies locales ou dans les circuits du commerce d’esclaves, l’importance de la prédation dans le fonctionnement du pouvoir, ou encore la manière dont ces sociétés légitiment la pratique prédatrice, cet ouvrage apporte un éclairage nouveau sur cette pratique