III International Conference

PP-II-9number of active Ni metal sites present on the catalytic surface of the multiphase samples orpresence of interphase boundaries. Co- and Fe -based catalysts contained the followingphases: CoAl, Co cub. ,Co hex. and Fe 3 Al, some traces of Fe и Fe 2 Al 5, respectively. However, theinitial conversions of CH 4 and CO 2 over the latter catalysts decreases in time in consequenceof agglomeration (sintering) of Co and formation of considerable quantities of FeO.Using scanning electron microscopy it was shown that some catalysts of carbon dioxidereforming of methane undergo nonessential morphological changes in redox conditions. Forexample, the surfaces of Ni 3 Al and Fe 3 Al loosened as a result of catalytic erosion and carbondeposition. The surface of metallic Fe transformed from globules to pyramidal particles.Therefore, catalytic activity decreased in consequence of carbonization. The coke filamentsformed on the surface of Co catalysts, therefore their activity decreased too.TG-DTA-analysis showed that the most coked catalysts lost 10-15% of their weight.Mass changes (TG and DTG curves) is accompanied by exothermal effect caused bycombustion carbon deposits formed during catalytic tests. At the same time, taking intoconsideration the possibility of formation of different forms of coke, the most significantweight change at 600 ºС (for Ni 3 Al), is caused by combustion of amorphous carbon whichburns out in the first place.In fact, with regard to the dry reforming reaction, the highest methane conversion hasbeen reached using Ni 3 Al and massive Co catalyst. Catalytic activity is a function of Ni andCo quantities in the intermetallides.178