Wolfson Nanoscience Laboratory, Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, UK.
Faraday Discuss. 2013;162:201-12. doi: 10.1039/c2fd20134h.
Industrial catalysts for the oxidation of methanol to formaldehyde consist of iron molybdate [Fe2(MoO4)3]. Using a variety of techniques we have previously shown that the surface of these catalysts is segregated in MoO3, and in order to understand the relationship between surface structure and reactivity for these systems we have begun a surface science study of this system using model, single crystal oxides. Model catalysts of molybdenum oxide nanoparticles and films on an Fe3O4(111) single crystal were fabricated by the hot-filament metal oxide deposition technique (HFMOD), where molybdenum oxides were produced using a molybdenum filament heated in an oxygen atmosphere. Low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and scanning tunnelling microscopy (STM) have been used to investigate molybdenum oxide nanoparticles and films deposited on Fe3O4(111). The molybdenum oxide film forms in the highest oxidation state, +6, and is remarkably stable to thermal treatment, remaining on the surface to at least 973 K. However, above approximately 573 K cation mixing begins to occur, forming an iron molybdate structure, but the process is strongly Mo coverage dependent.
工业甲醇氧化制甲醛催化剂为钼酸铁 [Fe2(MoO4)3]。我们之前采用多种技术表明，这些催化剂的表面是 MoO3 分相的，为了理解该体系表面结构与反应性之间的关系，我们开始采用模型单晶氧化物对其进行表面科学研究。采用热灯丝金属氧化物沉积技术（HFMOD）制备了 Fe3O4(111)单晶上的氧化钼纳米颗粒和薄膜模型催化剂，该技术使用在氧气氛围中加热的钼灯丝来产生钼氧化物。我们采用低能电子衍射（LEED）、X 射线光电子能谱（XPS）和扫描隧道显微镜（STM）研究了沉积在 Fe3O4(111)上的氧化钼纳米颗粒和薄膜。钼氧化物薄膜以最高氧化态 +6 形成，且对热处理非常稳定，在至少 973 K 时仍保留在表面。然而，高于约 573 K 时阳离子混合开始发生，形成铁钼酸盐结构，但该过程强烈依赖于 Mo 覆盖率。
