Chemisorption of ammonia on aluminosilica gels

Abstract

1. The chemisorption of ammonia on aluminosilicate catalysts was studied to determine the number of active centers participating in the catalytic process. The amount of chemisorbed ammonia decreases with increasing temperature according to an empirical equation. 2. On samples poisoned with sodium, ammonia is chemisorbed at low temperatures not only on the acid centers, but also on the cationic centers. To determine the acid centers only high-temperature chemisorption should be used. 3. The method of determining acid centers according to the chemisorption of ammonia is free of subjective errors, which are unavoidable in the determination of the transition of the nonionized state of the indicator to the ionized state. Another advantage of the method is the fact that the determination is conducted under conditions closer to those under which the catalyst exists during the chemical reaction (high temperatures, gas phase). 4. The use of the chemisorption of ammonia to determine the number of centers leads to the same results as other methods, namely, to a linear dependence of the catalytic activity on the number of acid centers and to constancy of the activities of the individual centers, regardless of the method of their preparation and the total surface of the sample.