RELATIONSHIP BETWEEN THE PLATINUM DISPERSION OF PLATINUM-SILICA-ALUMINA CATALYSTS AND THEIR CATALYTIC PROPERTIES

The acidity, catalytic activity, and platinum dispersion properties of four series of platinum-silica-alumina catalysts were measured and the relationship between these properties was studied. The acidity of the catalyst was varied by changing the Na poisoning conditions for and the alumina content of the carrier. The platinum dispersion condition was varied by changing the calcination temperature for and the platinum content of the catalyst. The results indicate that within certain ranges both the acidity and activity increase as platinum becomes more dispersed and both the activity and platinum dispersion increase as the acidity increases. In short, the acidity, activity, and platinum dispersion of the catalysts all tend to vary in a similar way. Furthermore, the isomerization activity of the catalysts varies as either the acidity or the platinum dispersion of the catalyst is varied; neither of these seems to be the rate controlling factor for this activity. These results can be explained by the postulate that the carrier and platinum components interact to form a surface catalyst complex. So there exist mutual influences between the acidity and platinum dispersion of the catalyst, and the catalytic activity thus varies with both of these properties. But the above results could hardly be explained by the separate centre theory since it would then seem that the property of one kind of separately existing centre should not influence that of the other kind and that either one or the other should control the reaction activity of a given catalyst.