Journal
RSC ADVANCES
Volume 8, Issue 21, Pages 11598-11607Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7ra11557a
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- [AAAA-A17-117041710079-8]
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The subject of this study was the content of oxygen in mixed oxides with the spinel structure Mn1.7Ga1.3O4 that were synthesized by coprecipitation and thermal treatment in argon at 600-1200 degrees C. The study revealed the presence of excess oxygen in low-temperature oxides synthesized at 600-800 degrees C. The occurrence of superstoichiometric oxygen in the structure of Mn1.7Ga1.3O4+ oxide indicates the formation of cationic vacancies, which shows up as a decreased lattice parameter in comparison with high-temperature oxides synthesized at 1000-1200 degrees C; the additional negative charge is compensated by an increased content of Mn3+ cations according to XPS. The low-temperature oxides containing excess oxygen show a higher catalytic activity in CO oxidation as compared to the high-temperature oxides, the reaction temperature was 275 degrees C. For oxides prepared at 600 and 800 degrees C, catalytic activity was 0.0278 and 0.0048 cm(3) (CO) per g per s, and further increase in synthesis temperature leads to a drop in activity to zero. The process of oxygen loss by Mn1.7Ga1.3O4+ was studied in detail by TPR, in situ XRD and XPS. It was found that the hydrogen reduction of Mn1.7Ga1.3O4+ proceeds in two steps. In the first step, excess oxygen is removed, Mn1.7Ga1.3O4+ Mn1.7Ga1.3O4. In the second step, Mn3+ cations are reduced to Mn2+ in the spinel structure with a release of manganese oxide as a single crystal phase, Mn1.7Ga1.3O4 Mn2Ga1O4 + MnO.
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