MS36-P05 In situ XRD and EXAFS/XANES study of xCuO-yAl2O3-zFe2O3 catalyst in reaction of CO oxidationThe Fe-based catalysts have been the subject of intense research in recent decades since wide application in various fields, such as water-gas shift reactions, Fisher-Tropsh synthesis, CO and hydrocarbons oxidation, ammonia synthesis. We are interesting in Fe-based system as effective catalysts for CO oxidation of gasification products of solid fuels in fluidized bed. CO is known to be the main product of gasification of dry fuels (coal, fuel oil, firewood).
One of the ways to stabilize catalyst from sintering, increase surface area and catalytic activity is using various promoters. Аt the same time, the introduction of different promoters affects the performance of the catalyst, i.e. shifts the temperatures of phase transformations and forms new mixed compounds. These effects strongly depends on the nature and amount of the incorporated metal cation.
We studied the influence of the nature and amount of promoter (Al and Cu cations) in Fe-O catalysts on the structural, textural, redox and catalytic properties of xCuO-yAl2O3-zFe2O3 samples in CO oxidation. In this work, we use in situ techniques (XRD and XANES/EXAFS) to study the behavior of catalysts and model systems under reduction in CO. Copper and aluminum can enter into iron oxide during the preparation stage, or during reduction with the formation of a solid solutions based on spinel or hematite structures .
Catalytic testing in the CO oxidation revealed the difference in catalytic properties for different modifiers. Catalysts contain Fe2O3, addition of Al atoms leads to a decrease of the oxide crystal size and copper contributes the formation of spinel structure. According to TPR-H2, Cu addition leads to improvement of reducibility of catalysts and decrease the temperatures of phase transformation.
Usually, reduction of iron oxide involves several steps including the formation of the intermediate oxides such as magnetite and wustite. The reduction of Fe2O3 to metallic Fe can be a two-step Fe2O3→Fe3O4→Fe or three-step Fe2O3→Fe3O4→FeO→Fe mechanisms (depending the temperature and H2O/H2 ratio) and affected the formation of metastable wustite.
Our in situ study shown that, introduction of aluminum in Fe2O3 leads to slowing down the reduction of Fe2O3 to Fe3O4 and the appearance of reaction products (FeO and Fe) at higher temperatures. The formation of the intermediate solid solution of Fe3- xAlxO4 and the formation in the reaction products of aluminum-containing spinel-type phases FeAl2O4 and Fe3-xAlxO4 are also observed. The introduction of Cu has an effect on the acceleration of the stage. FeO → Fe, and has little effect on the reduction of Fe3O4 → FeO / Fe.
Acknowledgement: This work was supported by RSF (project No. 17-73-20157).
 Estrella M. , Barrio , Zhou G., Wang X., Wang Q., Wen W., Hanson J.C., Frenkel A.I., & J.A. Rodriguez, (2009) J. Phys.Chem. C, 113. 14411-14417.Keywords: in situ XRD, spinel, catalyst