Martínez-Navarro Blanca, Sanchis Ruth, Asedegbega-Nieto Esther, Solsona Benjamín, Ivars-Barceló Francisco
Departmento de Química Inorgánica y Química Técnica, Facultad de Ciencias, UNED, Paseo Senda del Rey, 9, 28040 Madrid, Spain.
Instituto de Catálisis y Petroleoquímica (ICP-CSIC), C/Marie Curie, 2, Cantoblanco, 28049 Madrid, Spain.
Nanomaterials (Basel). 2020 May 21;10(5):988. doi: 10.3390/nano10050988.
Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (FeO) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized FeO particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °C). The solids obtained from a Fe (II)/Fe (III) nominal molar ratio of 4 showed higher specific surface areas which were also found to increase on lowering the reflux temperature. The starting 80 m g was enhanced up to 140 m g for the resulting optimized FeO-based solid consisting of nanoparticles with a 15 nm average diameter. On the other hand, Pd or Pd-Ag were incorporated post-synthesis, by impregnation on the highest surface FeO nanostructured substrate, using 1-3 wt.% metal load range and maintaining a constant Pd:Ag ratio of 8:2 in the bimetallic sample. The prepared nanocomposite materials were investigated by different physicochemical techniques, such as X-ray diffraction, thermogravimetry (TG) in air or H, as well as several compositions and structural aspects using field emission scanning and scanning transmission electron microscopy techniques coupled to energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic results from a preliminary reactivity study confirmed the potential of magnetite-supported (Ag)Pd catalysts for CH partial oxidation into formaldehyde, with low reaction rates, methane conversion starting at 200 °C, far below temperatures reported in the literature up to now; and very high selectivity to formaldehyde, above 95%, for FeO samples with 3 wt.% metal, either Pd or Pd-Ag.
已开发出基于负载在具有块状磁铁矿结构（FeO）的混合铁氧化物（II/III）上的贵金属单金属（Pd）或双金属（Ag/Pd）颗粒的纳米结构复合材料，以评估其在甲烷部分氧化中的多相催化应用潜力。将甲烷直接转化为增值化学品被公认为是确保未来可持续发展的关键。一方面，采用不同的Fe（II）/Fe（III）摩尔比（2或4）和回流温度（80、95或110°C），通过水基回流法合成了具有球形形态的纳米级FeO颗粒。从Fe（II）/Fe（III）标称摩尔比为4获得的固体显示出更高的比表面积，并且还发现随着回流温度的降低而增加。对于由平均直径为15nm的纳米颗粒组成的优化的基于FeO的固体，起始80mg增加到140mg。另一方面，在合成后通过浸渍在最高表面的FeO纳米结构基底上引入Pd或Pd-Ag，使用1-3wt.%的金属负载范围，并在双金属样品中保持恒定的Pd:Ag比为8:2。通过不同的物理化学技术对制备的纳米复合材料进行了研究，例如X射线衍射、在空气或H中的热重分析（TG），以及使用场发射扫描和扫描透射电子显微镜技术结合能量色散X射线光谱（EDS）的几种组成和结构方面。最后，初步反应性研究的催化结果证实了磁铁矿负载的（Ag）Pd催化剂将CH部分氧化为甲醛的潜力，反应速率低，甲烷转化率从200°C开始，远低于迄今为止文献报道的温度；对于含有3wt.%金属（Pd或Pd-Ag）的FeO样品，对甲醛的选择性非常高，高于95%。
