Catalytic and Structural Properties of Cobalt Surface Layers Formed in the Course of Self-Oscillatory Reactions

Self-oscillatory reactions of ethane oxidation (I) or CO oxidation (II) over Co foil at a temperature of 620 or 660°C, respectively, for 1 h caused the formation of a microporous surface layer composed of CoO crystals with sizes of 0.2–0.4 μm. In reaction (I), the crystals formed agglomerates with a size of ~1 μm with pores of the same size between them. The thickness of the microporous layer after type I treatment was ~0.7 μm. On the contrary, the agglomerates and pores were almost absent after type II treatment. The catalytic activity of foil samples with the microporous surface layers in the reactions of deep ethylene oxidation, CO oxidation, and CO methanation was measured. It was found that a maximal increase in the catalytic activity took place after type I treatment. The stability of the resulting porous layers in an inert (He), reducing (H 2 ), or oxidizing (O 2 ) atmosphere was studied upon heating to 750°C. A significant recrystallization and cracking of the layer were observed upon the inert-gas treatment. After heating in hydrogen, a strongly fixed surface layer with stable catalytic activity was formed. Finally, as a result of heating in an oxidizing atmosphere, the thickness of the surface layer increased to 6–8 µm; the main component was Co 3 O 4 , and its catalytic activity was minimal among the three cases.