Bulavchenko O A, Venediktova O S, Afonasenko T N, Tsyrul'nikov P G, Saraev A A, Kaichev V V, Tsybulya S V
Boreskov Institute of Catalysis SB RAS Lavrentieva Ave. 5 Novosibirsk 630090 Russia
Novosibirsk State University Pirogova Str. 2 Novosibirsk 630090 Russia.
RSC Adv. 2018 Mar 27;8(21):11598-11607. doi: 10.1039/c7ra11557a. eCollection 2018 Mar 21.
The subject of this study was the content of oxygen in mixed oxides with the spinel structure MnGaO that were synthesized by coprecipitation and thermal treatment in argon at 600-1200 °C. The study revealed the presence of excess oxygen in "low-temperature" oxides synthesized at 600-800 °C. The occurrence of superstoichiometric oxygen in the structure of MnGaO 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 °C; the additional negative charge is compensated by an increased content of Mn 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 °C. For oxides prepared at 600 and 800 °C, catalytic activity was 0.0278 and 0.0048 cm (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 MnGaO was studied in detail by TPR, XRD and XPS. It was found that the hydrogen reduction of MnGaO proceeds in two steps. In the first step, excess oxygen is removed, MnGaO → MnGaO. In the second step, Mn cations are reduced to Mn in the spinel structure with a release of manganese oxide as a single crystal phase, MnGaO → MnGaO + MnO.
本研究的对象是通过共沉淀法合成并在氩气中于600 - 1200°C进行热处理的具有尖晶石结构的MnGaO混合氧化物中的氧含量。研究发现，在600 - 800°C合成的“低温”氧化物中存在过量的氧。MnGaO氧化物结构中出现的超化学计量氧表明形成了阳离子空位，与在1000 - 1200°C合成的“高温”氧化物相比，这表现为晶格参数减小；根据XPS分析，额外的负电荷由Mn阳离子含量的增加来补偿。与高温氧化物相比，含有过量氧的低温氧化物在CO氧化反应中表现出更高的催化活性，反应温度为275°C。对于在600°C和800°C制备的氧化物，催化活性分别为每克每秒0.0278和0.0048立方厘米（CO），合成温度进一步升高会导致活性降至零。通过TPR、XRD和XPS详细研究了MnGaO的氧损失过程。发现MnGaO的氢还原过程分两步进行。第一步，去除过量的氧，MnGaO → MnGaO。第二步，尖晶石结构中的Mn阳离子被还原为Mn，同时释放出作为单晶相的氧化锰，MnGaO → MnGaO + MnO。
