Synthesis and Investigation of Finely Dispersed Calcium Aluminates and Catalysts Based on Them

Finely dispersed calcium aluminate C12A7 (12CaO⋅7Al 2 O 3 ) samples are synthesized in water and in an autoclave using supercritical drying. The specific surface area of the aerogel samples reaches 330 m 2 /g immediately after drying in an autoclave and 170 m 2 /g after calcination at 500°C. Nanocrystalline materials with a mayenite crystal structure and a specific surface area of about 80 m 2 /g are obtained after calcination at 600°C in water by the reaction of CaO with an aluminum hydroxide suspension. The supported catalysts containing Pd, V, Fe, Ni, Cu, and Ag are synthesized by incipient wetness impregnation of the C12A7 sample obtained in water. The catalytic activity of the synthesized samples is studied in the oxidation of carbon monoxide CO. The highest catalytic activity is demonstrated by the 1% Pd/C12A7 sample. Electron-acceptor sites capable of ionizing phenothiazine molecules to its radical cations, electron-donor sites ionizing trinitrobenzene to its radical anions, and radical sites reacting with diphenylamine to form stable nitroxyl radicals are observed on the surface of all the synthesized materials based on C12A7. The formation of nitroxide radicals after the adsorption of diphenylamine indicates that oxygen radicals on the mayenite surface, which can be highly active in various catalytic oxidation reactions, exist on the mayenite surface.