Search

Une étude critique des méthodes de préparation de catalyseurs monométalliques permet de voir que les techniques impliquant un échange (ionique ou chimique) conduisent à des catalyseurs à forte dispersion avec des moyens relativement simples. Au niveau de la caractérisation des catalyseurs, il ne semble pas exister de méthodes exhaustives permettant d'étudier les phases métalliques contenant des cristallites de taille inférieure à 1. 0 nm. Les techniques de microscopie électronique à haute résolution, la spectroscopie XPS et l'EXAFS semblent par contre les plus prometteuses. L'influence du support joue à plusieurs niveaux, en particulier sur la morphologie, la structure et sur les propriétés électroniques de la phase métallique. L'intérêt particulier d'étudier les effets de support résulte dans la création de phase métallique plus active et sélective. The current aim of catalyst research is to develop more and more active and selective dispersed metallic phases for a given reaction as well as to improve their stability. Catalytic properties depend directly on the physicochemical characteristics of the metallic phase (size of crystallites, composition, electron structure, interactions with the support). This is why improving such catalysts requires mastering synthesis routes and the characterizing of small supported metallic particles. The aim of this critical study is to highlight both the preparation methods leading to well-controlled monometallic phases and the physical techniques suited for characterizing them. By considering the metal-support entity as a veritable catalytic space, we have examined the direct influence of the nature of the support on the end characteristics of the metallic particles (morphology, structure, electron properties). We have found that impregnation techniques with an interaction (physical or chemical) can lead to high-dispersion metallic phases associated with a narrow dispersion of crystallite size. Among other techniques used, note will be taken of ion implantation, vapodeposition and radiolytic synthesis. Among overall and controlled-atmosphere characterization techniques, XPS and EXAFS spectroscopy were used to characterize, respectively, the electron properties and the crystalline structure (chemical environment) of metallic particles. Small metallic particles (less than 1. 0 nm in size) are more difficult to characterize because of the limitations of the physical techniques normally used. High-resolution electron microscopy was used for the local characterization of these small particles. The present results mainly concern the size of these small aggregates, but this technique also gives information on their morphology (aggregates of atoms, individual atoms in the aggregate) and on their crystalline structure (microdiffraction). Likewise, there is an entire domain of indirectcharacterization that is widely used, in which especially the accessibility and degree of oxidation reduction are measured of the metals by means of reagents or probe molecules (H2, O2, CO). However, this very precious information in the field of catalysis must always be compared with the result of direct characterization (size, electron properties). Concerning the influence of the support, this review shows that the metal-support pair is a full-fledged entity and that it is almost impossible to characterize it from the individual properties of the metal and of the support. At present, the principal results have to do with semiempirical classifications concerning the stability of metallic phases during heat treatments and with the influence of the metal-support interaction force on the morphology and electron properties of particles (load transfer, modifications of the electron structure of the transition metal).

Bien que la notion de transition écologique continue aujourd’hui à faire l’objet d’un processus de définition qui est loin d’être univoque, elle devient un enjeu de gouvernance municipale de plus en plus urgent. Dans les nombreuses situations où cette gouvernance est organisée de manière multiscalaire entre différents ordres de gouvernement ayant un certain nombre de compétences partagées, le problème de l’inexistence d’une définition stabilisée et opérationnelle de la transition se double du défi de l’identification et de la mise en oeuvre des actions à entreprendre. Cet article présente les résultats d’une recherche partenariale effectuée avec l’Arrondissement de Rosemont–La Petite-Patrie à Montréal autour de deux questions principales, à savoir « qu’est-ce que la transition écologique à l’échelle inframunicipale ? » et « comment la mettre en oeuvre ? ». L’analyse des documents et des interventions de ce partenaire a, entre autres, mené à la création de deux typologies : l’une sur les thématiques abordées et l’autre sur les types d’instruments utilisés. Les résultats ainsi obtenus permettent d’identifier trois défis pouvant être associés à cette gouvernance inframunicipale de la transition écologique, soit de concilier l’approche par les milieux de vie et la transition juste, de trouver des leviers pour les enjeux à responsabilité distribuée et de miser davantage sur les instruments réglementaires et incitatifs.

Copyright of Annales Historiques de la Révolution Française is the property of Librairie Armand Colin and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article provides a historical look at the concept of exercise in art by investigating the profession of actor in the second half of the 18th century. While a real theatromania takes hold of the French society, actors and actresses must meet the demands of an audience fond of new releases. We highlight practices that are less visible in the artistic work, such as memorizing roles, or organizing exercises within the first French drama school (1786-1789). We also show that the growing recognition of the centrality of both physical and intellectual exercises in the profession of actor helped defining the specificity of dramatic art in the second eighteenth century.

Copyright of Naturaliste Canadien is the property of La Societe Provancher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Recherches Feministes is the property of Groupe de Recherche et d'Echange Multidisciplinaires Feministes and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)