摘要
回流老化由ZrOCl2 水解得到的ZrO(OH) 2 水凝胶 ,然后经焙烧制备了高比表面积的ZrO2 .采用氮吸附、X射线衍射和FT Raman光谱等技术 ,研究了老化温度、老化时间、碱液的碱度和搅拌速度以及焙烧气氛对ZrO2 比表面积、晶相组成和晶粒大小的影响 .结果表明 ,回流老化可明显提高ZrO2 的比表面积和耐热性 .用比色法分析了样品中Si4+ 杂质的含量 ,结果表明 ,回流老化引起二氧化锆比表面积和热稳定性增大的主要原因是热碱溶液使玻璃容器中的Si4+ 溶解并掺杂至ZrO2 .样品中Si4+ 杂质含量愈大 ,ZrO2 的比表面积和热稳定性愈高 ,ZrO2 的晶粒愈小 .将ZrO(OH) 2 水凝胶在pH =11 5的NH4OH溶液中于 96℃回流老化 2 4h ,再经 6 0 0℃焙烧可获得比表面积高达 30 5m2 / g的无定形ZrO2 ;经 80 0℃焙烧可制得晶粒为 5 2nm ,比表面积为 174m2 / g的四方晶相ZrO2 .
High surface area zirconia samples were prepared by high temperature (600 similar to 800 degreesC) calcination of ZrOx(OH)(y) gel which was digested in basic solutions under different conditions. The obtained samples were characterized by XRD, FT-Raman, and nitrogen adsorption/desorption isotherms. It is shown that the digestion in basic solutions remarkably increases the specific surface area and thermal stability of zirconia. The effects of digestion temperature, time, pH and stirring speed on the sample properties were investigated. Under property controlled conditions, the digestion in aqueous NH4OH at pH = 11.5 leads to amorphous ZrO2 with a surface area of 305 m(2)/g after calcination at 600 degreesC; further calcination of the sample even at 800 degreesC produces tetragonal ZrO2 nanocrystals (ca 5.2 nm) with a surface area as high as 174 m(2)/g. Quantitative analysis of Si impurity in the samples revealed that the surface area increases with the increment of the Si4+ content in the samples, suggesting that incorporation of Si4+ ions from dissolution of glass vessels into zirconia is crucial for the increase of the surface area and for the stabilization of the very small (ca 5 similar to 6 nm) tetragonal ZrO2 nanocrystals.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2002年第3期214-218,共5页
基金
国家自然科学基金 (2 0 0 73 0 2 3 )和 (2 0 12 5 0 3 5 )资助项目
