The Selection of Catalysts by Thermogravimetry

Abstract

Thermogravimetry is used for rapid testing of catalysts. Studying the ammoxidation of propene we found that the activity of the catalysts depends on the amount of weight loss during heatingwithin a definite range of temperatures (150–250 ^°C). The weight loss results mainly from dehydration of the surface. It is compared with the conversion of propene, the yield of acrylo nitrile(ACN), the amount of CO and CO₂, the quantity of irreversibly adsorbed propene and the electrical conductivity. The results are explained by the nature of the OH species on the surface, which is changed with the distance between them i. e. with.their concentration on the surface. According to this distance different forms of oxygen are released on the surface if two hydroxyl groups are condensed and de-sorbed. The model is valid only within series of samples not too different in their stoichiometry and the technique of preparation.