Platinum-alumina catalysts, structure

L. L. Hegedus, and K. Baron (1975) Effects of poisoning and sintering on the pore structure and diffusive behavior of platinum/alumina catalysts in automotive converters, Journal of Catalysis 37(1) 127-132... 

STABILITY POISONS When water vapor is present in the sulfur dioxide-air mixture supplied to a platinum-alumina catalyst, a decrease in oxidation activity occurs. This type of poisoning is due to the effect of water on the structure of the alumina carrier. Temperature has a pronounced ejffect on... 

One of the most extensively used addition reactions of cyclobutanes is hydrogenolysis.36 With regard to the mechanistic aspect, evidence has been provided that hydrogenolysis of cyclobutane is structure sensitive to the particle size of the platinum on alumina catalysts.37 Moreover, a kinetic study has also revealed that the mechanism for the hydrogenolysis of cyclobutanes is likely to be different from that for cyclopropanes.37... 

Bimetallic catalysts based on platinum and tin, supported on y-alumina have become very important commercially. Platinum-tin catalysts are widely used in the dehydrogenation of alkanes. The structure of the catalyst and the role of tin have received a lot of attention. Recently Davis [1] reviewed the often contradicting literature about characterization of the bimetallic system. For the dehydrogenation reactions the main purposes with adding tin to a platinum catalyst are to increase the selectivity and stability towards coke formation. 

STRUCTURAL CONSIDERATION WITH RESPECT TO THE THERMAL STABILITY OF A NEW PLATINUM SUPPPORTED LANTHANUM-ALUMINA CATALYST... 

The catalytic layer of monolithic automotive reactors usually consist of active metals (Pt, Pd, Rh) supported on alumina. One of the most important problems set by these catalysts is the decrease in their activity after thermal exposure to the exhaust gas itself (Ref.l). It is well known that this thermal deactivation is directly related to the sintering of the active components. Moreover, this modification of the supported metal is drastically enhanced by structural changes of the support. Thus using TEM experiments, Chu et al (Ref. 2) have reported rapid sintering of platinum during the structural transition Y-AI2O3 to (X-AI2O3. 

Structural Consideration with respect to the Thermal Stability of a New Platinum Supported Lanthanum-Alumina Catalyst",... 

Hicks, R. F., Qi, H., Young, M. L. Lee, R. G. Structure sensitivity of methane oxidation over platinum and palladium. Journal of Catalysis 122, 280-294 (1990). Hicks, R. F., Qi, H., Young, M. L. Lee, R. G. Effect of catalyst structure on methane oxidation over palladium on alumina. Journal of Catalysis 122, 295-306 (1990). Bernal, S., Blanco, G., Gatica, J. M., Larese, C. Vidal, H. Effect of mild re-oxidation treatments with CO2 on the chemisorption capability of a Pt/CeOj catalyst reduced at 500°C. Journal of Catalysis 200, 411-415 (2001). 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

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