VPO超微粒子的制备和表征

以V₂O₅和浓H₃PO₄为原料,浓HCl和柠檬酸作还原剂,以含量不同金属离子为助剂,采用超临界流体干燥法制备了VPO超微粒子.应用BET、XRD、TEM及XPS等手段考察了VPO超微粒子的物性、结构及助剂对其物性的影响.实验结果表明,超临界流体干燥法可显著增大样品的比表面积,且可使粒子大小达到纳米尺度.实验发现,超微样品的晶相结构为一种尚未鉴定的未知物相.而表面V离子价态则基本上为+4价.

Preparation and Characterization of VPO Ultrafine Particles

VPO ultrafine particles were first successfully prepared by the supercritical fluid drying(SCFD). BET, XRD, TEM and XPS techniques were used to investigate the specific surface area, the phase composition, the grain size and the oxidation state of various samples. The VPO ultrafine particles after SCFD were activated in the reactant mixture or nitrogen at 673 K for 6 h. The results indicated that the obtained VPO ultrafine particles have a larger specific surface area, much smaller particle size and an unidentified crystalline phase in some cases after SCFD and activation. The kind and amount of promoter used and the activation atmosphere affect the physical properties of the VPO ultrafine particles. An ultrafine particle with Zr\+\{4+\}and Mo\+\{6+\} promoters, a surface area of 175.6 m\+2/g and grain size of smaller 50 nm, can be obtained by activating in the nitrogen atmosphere at 673 K for 6 h. The oxidation state of surface vanadium atoms of ultrafine particles was around +4, similar to that of vanadium in (VO)\-2P\-2O\-7. The surface P/V molar ratio is in the range of 1.04\_1.46, and is a little higher among the samples activated in N\-2 atmosphere. Primary property evaluating results indicated that the small VPO particles showed very high selectivity but relatively low conversion.