INTERACTION OF THE Fe/γ-Al2O3 CATALYTIC SYSTEM WITH PROBE MOLECULES III. STUDY OF THE INTERACTION OF AMMONIA WITH γ-Al2O3 OXIDE AND THE Fe/γ-Al2O3 SYSTEM
Ключевые слова:
heterogeneous catalysis, physicochemical research methods, adsorbed molecules.Аннотация
The work is devoted to the study of the interaction of heterogeneous catalytic systems with adsorbed
molecules. It presents the results of the interaction of the initial γ-Al2O3 oxide and the Fe/γ-Al2O3 system with
ammonia obtained using IR spectroscopy and the method of temperature programmed desorption.
Lewis and Bronsted acid centers were detected on the surface of both γ-Al2O3 oxide and the Fe/γ-Al2O3 system
during their interaction with ammonia in the temperature range 293-773K using IR spectroscopy. The relative
intensity of the absorption bands corresponding to these centers depends on the temperature of interaction with
ammonia.
It was found by ammonia TPD that adsorbed NH3 is desorbed in the form of five peaks from the γ-Al2O3 surface
on a temperature scale, and in the form of seven peaks from the surface of the Fe/γ-Al2O3 system. It was shown that
the total amount of desorbed ammonia decreases markedly with increasing adsorption temperature. Moreover, for
individual temperature peaks, the amount of adsorbed ammonia can either decrease, pass through an extremum, or
remain approximately constant. The appearance of additional desorption peaks for the Fe/γ-Al2O3 system is
associated with iron deposited on alumina.
Proceeding from the temperature range of existence of desorption peaks for γ-Al2O3 oxide and the Fe/γ-Al2O3
system it was established that they contain weak acid centers (desorption temperature up to 523K), acidic centers of
medium strength (desorption temperature from 523 to 613K) and strong acid sites (desorption temperature above
613K). The volume of desorbed ammonia in the indicated temperature ranges can serve as a quantitative measure of
various types of acid sites.
