钴系复合催化材料在费托反应前后的结构变化研究

钴系催化材料在费托合成中的反应已有较多研究文献,但对费托反应前后由于水热环境导致钴系催化材料发生结构变化的研究则很少。应用场发射扫描电子显微镜研究了3种新鲜制备的钴系复合催化材料的织构特征,应用粉末X射线衍射技术研究了费托反应前后3种钴系催化材料的结构变化;并且发现含有氧化铝成分的样品在经历费托反应的水热环境之后均在衍射角(2θ)为21.5和23.8°处出现新物相的衍射峰,即形成某种结晶性水合氧化铝;该新物相可能与被H2O氧化的钴物种发生反应生成无催化活性的Co Al2O4相而导致钴催化剂的衰减失活。     

Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum−iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H₂O₂ as the oxidant at phenol : H₂O₂ mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.     

Investigation on nanocrystalline iron‐cobalt‐vanadium alloy processed by equal channel angular pressing (ECAP)

Nanocrystalline iron‐cobalt‐vanadium alloy was fabricated by Equal‐Channel Angular Pressing (ECAP). Microstructural evolution at different passes of ECAP and the effect of φ in the ECAP were researched. The results revealed that a phase slowly turned to γ phase and followed the form of dislocation cells in the iron‐cobalt‐vanadium alloy with the increase of severe plastic deformation. At last, it became reasonably finer bands of subgrains. The results with intersect at an angle φ of 90° was better than with at an angle φ of 120°. After three passes of ECAP, at an angle φ of 90°, the nanocrystalline microstructure could be obtained. The grain size was reduced from 30 μm in the initial state to 400nm.     

原位CuYSi颗粒增强块体镁基非晶合金复合材料的研究

用Mg-4%Si合金、纯Cu、纯Mg、Cu-38%Y合金经普通铜模铸造方法制备了一种原位颗粒增强Mg60Cu30Y10块体非晶合金复合材料。运用XRD以及EDS确定其颗粒为CuYSi相,采用SEM-EDS对颗粒的形貌、大小及成分进行了分析,并对Mg60Cu30Y10块体非晶合金复合材料的硬度及热稳定性进行了研究。结果表明,原位生成的CuYSi颗粒尺寸细小(10μm左右),形状规整并且均匀分布在非晶合金基体上;与Mg60Cu30Y10块体非晶合金相比,CuYSi颗粒的生成使得非晶合金复合材料的硬度增加102.5HV,ΔTx增加6.1K。