Oxide Support (oxide + support)

Distribution by Scientific Domains


Selected Abstracts


On the graphitisation role of oxide supports in carbon nanotube CVD synthesis

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008
M. H. Rümmeli
Abstract In this contribution we present various data from CNT grown from supported catalysts. The observed data are in agreement with the catalyst volume to surface area model developed for floating catalysts and which predicts a direct CNT diameter and number of wall dependence on the catalyst size. Further, our studies point to the root of a CNT lying at the support rather than the catalyst. Additional supporting studies point to oxygen playing a critical role in the growth of CNT, viz. the CNT can grow from an oxide support rather than the catalyst. In this scenario the catalysts role is twofold; to precipitate carbon from the catalyst,carbon eutectic upon supersaturation and thus form the embryonic caps and to form circular defect sites at its circumference on the oxide support. These circular defect sites enable continued CNT growth directly from the support. Our findings point to catalytic processes very reminiscent of many other heterogeneous catalytic processes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Magnetically Separable Gold Catalyst for the Aerobic Oxidation of Amines

CHEMCATCHEM, Issue 1 2009
Linda Aschwanden
Abstract A magnetically separable, recyclable gold catalyst consisting of gold nanoparticles supported on intimately mixed superparamagnetic ceria/iron oxide has been prepared by simple addition of the preformed mixed oxide support and the gold precursor, Au(OAc)3, to the reaction mixture of the aerobic oxidation of amines. The catalyst was characterized by means of X-ray diffraction (XRD), N2 adsorption, superconducting quantum-interference device (SQUID) measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning transmission electron microscopy (STEM), and scanning electron microscopy with an energy-dispersive X-ray spectrometer (SEM-EDAX). Catalytic tests with various amines showed high selectivity to the corresponding imines (87,100,%), and good separation efficiency and recyclability of the catalyst. [source]


Direct Dehydrogenative Amide Synthesis from Alcohols and Amines Catalyzed by ,-Alumina Supported Silver Cluster

CHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009
Ken-ichi Shimizu Dr.
Silver clusters immobilized on ,-Al2O3 catalyze direct amide synthesis from alcohols and amines in the presence of catalytic amount of weak base (Cs2CO3). The reaction proceeds by cooperation of the coordinatively unsaturated silver site, as well as acid and base sites of the oxide support (see scheme). [source]


CO Combustion on Supported Gold Clusters

CHEMPHYSCHEM, Issue 9 2006
Matthias Arenz Dr.
Abstract Recent progress in the understanding of the fascinating catalysis of CO combustion by supported gold particles is summarized. Focusing on size-selected gold clusters consisting of only a few atoms, that is, the size regime with properties nonscalable from the bulk properties, we discuss the current knowledge of the different factors controlling the reactivity at the molecular level. These factors include the role of the oxide support, its defects, cluster charging as well as the structural fluxionality of clusters, the cluster size dependency, and the promotional effect of water. By combining experimental results with quantum mechanical ab initio calculations, a detailed picture of the reaction mechanism emerges. While similar mechanisms might be active for gold nanoparticles in the scalable size regime, it is shown that for different systems (defined by the cluster size, the support, experimental conditions, etc.) the reaction mechanism differs and, hence, no generalized explanation for the catalytic driving force of small gold particles can be given. [source]