Malyshev Sergey A, Shlyakhtin Oleg A, Loktev Alexey S, Mazo Galina N, Timofeev Grigoriy M, Mukhin Igor E, Svetogorov Roman D, Roslyakov Ilya V, Dedov Alexey G
Department of Chemistry, M.V. Lomonosov Moscow State University, 119991 Moscow, Russia.
Department of Materials Sciences, Shenzhen MSU-BIT University, Shenzhen 518172, China.
Materials (Basel). 2022 Oct 18;15(20):7265. doi: 10.3390/ma15207265.
In order to clarify the role of RO in the metal-oxide catalysts derived from complex oxide precursors, a series of RCaNiO (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the RCaNiO structure (KNiF type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of RCaNiO in the Ar/H gas mixture at 800 °C causes a formation of dense agglomerates of CaO and RO coated with spherical 25-30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(RO,CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700-800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of RO components of the composite catalysts. The maximum CH conversion in POM reaction was observed for Ni/(SmO,CaO), while the maximum selectivity was demonstrated by NdO-based composite. The possible reasons for the observed difference are discussed.
为了阐明RO在由复合氧化物前驱体制备的金属氧化物催化剂中的作用，制备了一系列RCaNiO（R = Nd、Sm、Eu）复合氧化物。从Nd到Eu，RCaNiO结构（KNiF型，Cmce）的正交畸变有显著的系统性增加，这与它们离子半径的相应减小相关。在800℃的Ar/H气体混合物中对RCaNiO进行还原，会形成由CaO和RO组成的致密团聚体，这些团聚体表面包覆着25 - 30 nm的球形Ni金属颗粒。在本研究的所有Ni/(RO,CaO)复合材料中，金属颗粒和氧化物团聚体的尺寸相似。它们的形态与通过复合氧化物部分还原获得的氧化还原析出现象的产物相当相似。所有制备的复合材料在700 - 800℃下对甲烷的干重整（DRM）和部分氧化（POM）均表现出显著的催化活性。从Nd到Eu，复合材料的DRM催化活性系统性降低可归因于复合催化剂中RO组分碱性的降低。在POM反应中，Ni/(SmO,CaO)的CH转化率最高，而基于NdO的复合材料表现出最高的选择性。文中讨论了观察到这种差异的可能原因。
