Réactivité des petites particules métalliques de Ni° hautement dispersées sur zéolithes X échangées par des ions Ce

La composition du support zéolithique dans les systèmes Ni2+zéolithe X (acidité, présence d'autres cations) a une importance déterminante dans l'obtention d'un état métallique de nickel bien dispersé. Selon la taille des particules métalliques obtenues, le nickel présente des propriétés hydrogénolysantes, hydrogénantes et de chimisorption considérablement modifiées. Au dessous d'une certaine taille (d ≤ 12 Å), le nickel perd ses propriétés catalytiques et chimisorptives. Une étude par thermodésorption programmée de ces systèmes a mis en évidence une phase constituée "d'espèces hydrogènes" fortement chimisorbées à la surface des particules, formées lors du processus de réduction, qui inhibent tout contact entre les sites actifs du nickel et les réactifs

Masking of Several Olfactory Notes by Infra-threshold Concentrations of 2,4,6-Trichloroanisole

Introduction Among wine defects, 2,4,6-trichloroanisole has a specific impact on wine perception. In addition to giving to the wine an unpleasant odor, 2,4,6-trichloroanisole has a masking effect on notes. In this study, the specificity and efficacy of the masking effect of 2,4,6-trichloroanisole was tested at infra- and supra-threshold concentrations. A simplified model of a binary mixture was also studied for in-depth analysis of this phenomenon. Methods Techniques used included sensory analysis (odor profiling), psychophysical tests (threshold measurement and triangle test), chemical analyses (GC-MS), and a mono/dichorhinic stimulation paradigm, to test the hypothesis of peripheral interaction. Results The results revealed that TCA had a masking effect on a range of aromatic notes, even at infra-threshold concentrations. However, they also showed counteraction of odorant specificity by 2,4,6-trichloroanisole. The origin of this masking effect was also discussed. The results suggested that this interaction can be assumed to take place at receptor level. Conclusion This study provided experimental confirmation of the widespread idea that constituents in non-perceptible concentrations influence the perceived quality of mixtures of odorous compounds. Implications Moreover, this type of olfactory model may improve our understanding of combinatorial olfactory encoding at the peripheral level