Chemical probes unsupported

Having in consideration the problem of chemical probing of Pd/support systems, it is relevant to know the catalytic properties of unsupported palladium. Three types of reactions will be considered in this article ... 

The final probe of molecular clusters is that of selected chemical reactions. The use of probe reactions to study supported cluster catalysts is well established, and we are attempting the development of similar probes of unsupported clusters. The first steps in this direction are the design of a pulsed chemical reactor to go with the pulsed cluster source and the development of criteria for reactions. It is important to recall that at present... 

This review is followed by a consideration of some of the features characteristic of hydrocarbon reactions on catalysts comprising individual metals from Groups VIII and IB of the periodic table. Finally, the activities of a series of unsupported nickel-copper alloys for hydrogenolysis and dehydrogenation reactions are discussed. These latter studies were made to obtain information on the selectivity phenomenon with bimetallic catalysts of known structure. The nickel-copper alloys were characterized by a variety of chemical and physical probes. 

A problem, different in nature, that needs additional attention refers to the characterization of the active centers involved in adsorption and catalytic processes and particularly to the estimation of the number of metallic centers and the exposed surface in supported and unsupported perovskites. A number of chemical and physical methods have been used for metals and oxides, and those based on selective chemisorption of probe molecules seem to be the most promising for this purpose (307). However, while considerable progress has been made for supported metals, no method has been accepted for oxides. This has been caused by the comparatively complex nature of these latter compounds where oxide ions and metal ions of different oxidation states may be present. As probe molecules, O2, CO, and NO were the most frequently used (307) the 02 chemisorption presents the problems inherent to any method based on gas adsorption at low temperatures (a large fraction of physisorbed gas accompanying the chemisorption). On the other hand, its symmetric character renders this molecule unamenable to study by IR spectroscopy. Nonetheless, this method has been used with some success by Weller et al. (308-310) on simple oxides, and its possible application to perovskites and other mixed oxides should be explored. Previous chemisorption work... 

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