Niobia-based magnetic nanocomposites were prepared by covering magnetite nanoparticle cores (Fe₃O₄, MNP) with either Nb₂O₅ or Nb₂O₅-SiO₂ shells using a two-step procedure. In the first step magnetite nanoparticles were prepared by the coprecipitation method. The second step involved their coverage with either Nb₂O₅ shells, through a precipitation method, or with Nb₂O₅-SiO₂ shells, through a sol-gel protocol followed by precipitation in the presence of the CTAB surfactant. The obtained materials were exhaustively characterised by X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, ICP-OES, DRIFT and Raman spectroscopy, and CO₂ - and NH₃-TPD measurements, and investigated for glucose dehydration to HMF. The catalytic performances were directly correlated to the nature of the supported niobia phases, which, in turn, has been dictated by the niobia content and the preparation route. The high selectivity to HMF was correlated with to the large pseudohexagonal niobium oxide (TT-Nb₂O₅) phase while the catalytic activity was directly correlated to the small nanoparticles size. A proper combination of these features led to an optimum catalytic system for the selective production of HMF through glucose dehydration. A third important feature making the developed catalyst promising is its magnetic property, ensured by the magnetite nanoparticles core. This allowed its easy separation from the reaction products.

通过分两步程序用Nb ₂ O ₅或Nb ₂ O ₅ -SiO ₂壳覆盖磁铁矿纳米颗粒核（Fe ₃ O ₄，MNP）来制备基于纳米比亚的磁性纳米复合材料。第一步，通过共沉淀法制备磁铁矿纳米颗粒。第二步涉及通过沉淀法用Nb ₂ O ₅壳或Nb ₂ O ₅ -SiO ₂覆盖它们。壳，通过溶胶-凝胶协议，然后在CTAB表面活性剂的存在下沉淀。通过X射线衍射，Mössbauer光谱，磁测量，ICP-OES，DRIFT和拉曼光谱以及CO _2-和NH ₃ -TPD测量对得到的材料进行了详尽的表征，并研究了葡萄糖脱水为HMF。催化性能与负载的纳米比亚相的性质直接相关，而纳米比亚的含量和制备途径则决定了负载的纳米比亚相的性质。对HMF的高选择性与较大的假六方铌氧化物（TT-Nb ₂ O ₅）相，而催化活性与小纳米颗粒尺寸直接相关。这些特征的适当组合导致通过葡萄糖脱水选择性生产HMF的最佳催化体系。使开发的催化剂有前景的第三个重要特征是其磁性，这是由磁铁矿纳米颗粒核确保的。这使得其易于与反应产物分离。