Effect of initial nickel and iron oxide morphology on their structural transformation in CO/H 2 mixture

Abstract

The NiO and α-Fe 2O 3 samples from various backgrounds were used as precursors of the catalysts for CO hydrogenation. The effect of the initial microstructure of oxides on the morphological peculiarities and catalytic properties of the newly formed catalysts was studied using transmission electron microscopy and in situ XRD combined on-line with gas-chromatographic analysis. The initial morphology of precursors is found to be responsible for the direction and regularity of the solid-gas reactions yielding the catalyst, as well as for the ‘architecture’ and activity of the catalysts obtained: (i) NiO with the best developed plane (111) transforms into Ni 3C/NiO catalyst consisting of platelet oxide particle covered by Ni 3C microcrystals and producing the equal amounts of CH 4 and CO 2; disordering of the plane (111) induced by SD + HP leads to the formation of Ni/Ni 3C/NiO catalyst consisting of the polycrystalline phases, whose catalytic properties improved; (ii) NiO with the best developed plane (100) transforms into Ni/Ni 3C/NiO catalyst containing NiO microcrystals covered by Ni(100) and polycrystalline Ni 3C and giving CH 4 as a major product of reaction; action of SD + HP results in the formation of Ni/Ni 3C/NiO catalyst containing polycrystalline Ni and Ni 3C phases, whose catalytic properties degraded. Similar correlation is observed for the catalysts prepared from α-Fe 2O 3.