Support particular metal studies

In particular, catalytic aerobic oxidations of carbohydrates, using supported noble metals in the liquid phase, have been extensively studied by... 

There have been numerous magnetic susceptibility and NMR studies of carboxylates, particularly those systems containing bridging coordination. Such studies have revealed much information about the metal interactions, often with valuable support from ESR, electronic and mass spectrometry. Yet still these techniques cannot be said to yield, sufficiently frequently, definitive information about the mode of coordination without the support of diffraction studies. 

The efficiency and selectivity of a supported metal catalyst is closely related to the dispersion and particle size of the metal component and to the nature of the interaction between the metal and the support. For a particular metal, catalytic activity may be varied by changing the metal dispersion and the support thus, the method of synthesis and any pre-treatment of the catalyst is important in the overall process of catalyst evaluation. Supported metal catalysts have traditionally been prepared by impregnation techniques that involve treatment of a support with an aqueous solution of a metal salt followed by calcination (4). In the Fe/ZSM-5 system, the decomposition of the iron nitrate during calcination produces a-Fe2(>3 of relatively large crystallite size (>100 X). This study was initiated in an attempt to produce highly-dispersed, thermally stable supported metal catalysts that are effective for synthesis gas conversion. The carbonyl Fe3(CO) was used as the source of iron the supports used were the acidic zeolites ZSM-5 and mordenite and the non-acidic, larger pore zeolite, 13X. 

Transition Metal Salts and Oxides on Alumina. Transition metal salts, particularly chlorides and nitrates, are frequently used as starting materials for the preparation of supported transition metal oxides or supported precursors for supported metal catalysts. Also, many catalytic materials, particularly supported molybdenum and tungsten oxide and sulfide catalysts, contain transition metal ions, namely Co, Ni , and Fe " as promoters. Thus, it is interesting to study the spreading and wetting behavior of salts of these transition metals and of their oxides. This is of particular importance for promoted catalyst materials, since in practice the incorporation of the active phase and the promoter should be possible in one step for economic reasons. 

Methane oxidation at mild or low temperatures can be catalyzed by platinum group metals. Palladium is one of the most efQdent metals (1) and has been studied over mai supports (2-6). This particular metal, when supported on alumina, b ins to show an increase in its activity between 350 and 420°C. At these conditions a general increase in the active spedes particle size is observed. Piimet and Briot (7,8) defined two states for the Pd/Al203 supported catalyst a state I, obtained after simple reduction and a state n after the catalyst had reacted at 600°C for 14 h under 02/CH4=4A. State II was more active than state I and showed a lower binding oietgy of oxygen with palladium. However, the state of the active phase was not clear. The diffoences in activity, also observed by others, have also been related to the formation/decomposition of PdO (9), to the oxygen adsorbed on metallic Pd (2), to the modification of Pd surface spedes (3), and to the reconstruction of PdO crystallites (4, 10). One of the hypotheses for the activation of the Pd catalysts was the establishment of an epitaxy between the metal and the support (8, 11). 

While the use of a support or carrier stabilizes small metal crystallites against growth and surface area loss, reactions of support and metal may occur, especially if the catalyst is subjected to elevated temperatures The main factors affecting these phenomena are temperature, time of exposure and atmosphere. Most previously reported sintering studies were for supported platinum and particularly for Pt/AlgOj catalysts (1,2). Considerably less information is available on the sintering of other supported metal catalysts (3,4), and thus there is very little information on the behavior of bimetallic catalyst systems such as supported platinum-rhodium. 

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