Реферат: Alumina-based catalysts are widely used in chemical and petrochemical industries due to the unique properties of alumina including high thermal stability and large specific surface area, which are important for the dispersion of active components. A classic example of such catalysts operating at high temperatures is three-way catalysts applied for purification of vehicle exhaust gases. Since the temperature of these gases can be significantly elevated, the catalysts undergo sufficient deactivation during the operation runs. All this motivates both the researcher and manufacturers to search for efficient ways to prevent the deactivation processes or to regenerate the spent catalysts. On the other hand, there is a growing interest to the systems with low loading of the precious metals in a highly dispersed state, showing a superior activity in CO oxidation. Among them, palladium and rhodium are still considered as the most active components. For such systems, the detectable content of these metals after the real operation runs (or simulated aging procedures) diminishes significantly. Thereby, an adequate analysis of the aged catalyst using traditional experimental techniques seems to be complicated or even impracticable task. In general, the drastic aging conditions can initiate a number of deactivation processes of the active components deposited on γ-Al2O3 and La or Zr doped γ-Al2O3 commercial supports, such as migration, agglomeration, and bulk diffusion. Recently, the methods of UV-vis and luminescence spectroscopies were found to be informative for diagnostics of rhodium and palladium concentration and state, thus giving the possibility to follow any changes taking place during the aging procedures. The use of bimetallic catalysts was proven to be a prospective approach to improve the thermal stability of the initial high-dispersed state of the active metals due to the strengthened metal-metal and metal-support interactions. For the bimetallic Pd-Rh/La-Al2O3 system containing 0.12 wt.% Pd and 0.08 wt.%Rh, a strong metal-metal interaction enhances the resistance of palladium towards agglomeration at high temperature and prevents diffusion of rhodium ions into the bulk of the support. In the report, particular attention will be paid to the state of lanthanum in the La-Al2O3 systems during the hydrothermal treatment under mild conditions, which simulate the slurrying and washcoating procedures. An agglomeration of the highly dispersed La2O3 particles weakly bonded with the alumina during such a treatment leads to the formation of LaAlO3 after the calcination in a temperature range of 800–1100 °C. The luminescence technique proposed in the present report is considered as a powerful tool to estimate the amount of LaAlO3 species, starting from such a low concentration as 0.1 wt.%. The agglomeration process of the La2O3 particles serves as an indicator of the possible formation of new phases, which can include as lanthanum as active metals, thus affecting the properties of the catalyst in a whole.

Библиографическая ссылка: Stoyanovskii V.O. , Plyusnin P.E. , Shubin Y.V. , Vedyagin A.A.
Application of Diffuse Reflectance UV-vis and Luminescence Spectroscopies for Characterization of Alumina-based Catalysts
16th International Conference on Fundamental and Applied Aspects of Physical Chemistry 26-30 Sep 2022