制备化学对钒磷氧催化剂物理性质影响的考察——I.溶胶—凝胶法及常规制备法

THE EFFECTS OF PREPARATION CHEMISTRY ON THE PHYSICO PROPERTIES OF VPO CATALYSTS ——Ⅰ.SOL GEL AND OTHER COMMON PREPARATION METHODS

应用 Ｂ Ｅ Ｔ、 Ｘ Ｒ Ｄ、 Ｔ Ｅ Ｍ 等手段研究了由溶胶—凝胶法及常规制备法制备的钒磷氧催化剂的比表面积，晶相组成，晶粒大小等物理性质．发现制备化学因素对钒磷氧催化剂物理特性的影响比较复杂，尤其是不同方法之间所表现出的差异比较明显．由有机相中制备时可以获得单一 Ｂ 相，且晶相组成与晶粒尺寸受制备条件的影响相对较小．实验结果表明包括溶胶—凝胶法在内的几种制备方法制得的催化剂粒子较大，分布不均，且比表面积较小．通过本研究提出了制备大比表面积小粒子 Ｖ Ｐ Ｏ 催化剂的其它可能途径．

BET,XRD and TEM techniques were used to investigate the effects of preparation chemistry on the physico characteristics of VPO catalysts prepared by four methods.In the first method,ammonium metavanadate and phosphoric acid were used as row materials, hydrochloric acid as reductive agent and oxalic acid as solvent media. In the second, Vanadium pentoxide and phosporic acid as vanadium and phosphorus sources, hydrochloric acid and citric acid as reductive agent and solvent rspectively .In the third method,the vanadium and phosphorus sources are the same as used in the method two ,but isobutanol and benzalcohol were adopted as reductive agent and solvent respectively.In the last method,the reductive agent was azanol hydrochloric acid instead.The P/V ratio was in the range of 1.1 1.2 for all preparation methods. The first methods were the typical sol gel procedures.The results revealed that the surface area,the phase composition, the crystallinity as well as the grain size were varied with the row materials used ,the ratio of P/V , the types and content of solvent and the calcination process. The typical sol gel and other two common preparation methods adopted in this study all gave the low surface area(<10m 2/g) and large particle(>1μm) of VPO catalysts. The size distribution was also inhomogeneous. It was found that the method three can produce almost pure B or (VO) 2P 2O 7 phase and the phase composition was minimally affected by altering the calcination conditions. Through this study, it is realized that the drying process for the sample gel is very important to obtain the small particles of the VPO system. In order to prevent the small gel particles with high surface free energy from aggregation into large dumpling during the drying process, other preparation procedure should be taken into consideration, for example, the supercritical drying for methods one and two. On the other hand,for method three, the mechanical milling could be another effective and alternative way to obtain the small particles of VPO catalysts which contain large capacity of surface lattice oxygen. The primary tests in our lab have already supported these assumes.