Cherepanova Svetlana V, Koemets Egor G, Gerasimov Evgeny Yu, Simentsova Irina I, Bulavchenko Olga A
Boreskov Institute of Catalysis SB RAS, Lavrentiev Ave., 5, Novosibirsk 630090, Russia.
Department of Physics, Novosibirsk State University, Pirogova, 2, Novosibirsk 630090, Russia.
Materials (Basel). 2023 Sep 14;16(18):6216. doi: 10.3390/ma16186216.
The reduction of Co-based oxides doped with Al ions has been studied using in situ XRD and TPR techniques. Al-modified CoO oxides with the Al mole fraction Al/(Co + Al) = 1/6; 1/7.5 were prepared via coprecipitation, with further calcination at 500 and 850 °C. Using XRD and HAADF-STEM combined with EDS element mapping, the Al cations were dissolved in the CoO lattice; however, the cation distribution differed and depended on the calcination temperature. Heating at 500 °C led to the formation of an inhomogeneous (Co,Al)O solid solution; further treatment at 850 °C provoked the partial decomposition of mixed Co-Al oxides and the formation of particles with an Al-depleted interior and Al-enriched surface. It has been shown that the reduction of cobalt oxide by hydrogen occurs via the following transformations: (Co,Al)O → (Co,Al)O → Co. Depending on the Al distribution, the course of reduction changes. In the case of the inhomogeneous (Co,Al)O solid solution, Al stabilizes intermediate Co(II)-Al(III) oxides during reduction. When Al ions are predominantly on the surface of the CoO particles, the intermediate compound consists of Al-depleted and Al-enriched Co(II)-Al(III) oxides, which are reduced independently. Different distributions of elemental Co and Al in mixed oxides simulate different types of the interaction phase in CoO/γ-AlO-supported catalysts. These changes in the reduction properties can significantly affect the state of an active component of the Co-based catalysts.
采用原位XRD和TPR技术研究了掺杂铝离子的钴基氧化物的还原过程。通过共沉淀法制备了铝摩尔分数Al/(Co + Al) = 1/6、1/7.5的Al改性CoO氧化物，并在500和850℃下进一步煅烧。利用XRD、HAADF-STEM结合EDS元素映射分析表明，Al阳离子溶解在CoO晶格中；然而，阳离子分布不同，且取决于煅烧温度。在500℃加热导致形成不均匀的(Co,Al)O固溶体；在850℃进一步处理促使混合Co-Al氧化物部分分解，并形成内部贫铝、表面富铝的颗粒。结果表明，氧化钴被氢气还原通过以下转变过程：(Co,Al)O → (Co,Al)O → Co。根据Al的分布情况，还原过程会发生变化。对于不均匀的(Co,Al)O固溶体，Al在还原过程中稳定中间的Co(II)-Al(III)氧化物。当Al离子主要位于CoO颗粒表面时，中间化合物由贫铝和富铝的Co(II)-Al(III)氧化物组成，它们独立还原。混合氧化物中元素Co和Al的不同分布模拟了CoO/γ-AlO负载型催化剂中不同类型的相互作用相。还原性能的这些变化会显著影响钴基催化剂活性组分的状态。
