摘要
研究了浸渍偏钨酸铵和仲钼酸铵的无定形ＺｒＯ２在焙烧过程中钨和钼氧化物表面分散和晶相变化情况．发现于３５０℃焙烧后钨、钼仍以多聚酸根形式分散于ＺｒＯ２表面，用ＸＲＤ法测定的“视阈值”远大于按ＷＯ３和ＭｏＯ３计算的单层分散容量．８００℃焙烧后钨和钼以ＷＯ３和ＺｒＭｏ２Ｏ８的形式分散于ＺｒＯ２表面上，用ＸＲＤ方法测定的“视阈值”与ＷＯ３和ＺｒＭｏ２Ｏ８的单层分散容量相近．Ｈａｍｍｅｔｔ指示剂法和正戊烷异构化反应结果表明，ＷＯ／ＺｒＯ２体系的Ｈｏ可达－１３．８～－１４．５，ＭｏＯ３／ＺｒＯ２体系的Ｈｏ可达－１２．０～－１２．７．８００℃焙烧的ＷＯ３和ＭｏＯ３含量在单层分散容量附近的样品超强酸性最强．
The dispersion and crystal phase changes of tungsten and molybdenum compounds on samples prepared by impregnating ammonium metatungstate and ammonium paramolybdate on amorphous ZrO2 during the calcination have been investigated in detail. It was found that after the calcination at 350℃ tungsten and molybdenum existed in the form of isopolyacidic anions,so that the apparent dispersion thresholds determined by XRD method were much greater than the calculated monolayer dispersion capacities of WO3 and MoO3 on ZrO2.After calcination at 800 ℃ the W and Mo dispersed on ZrO2 transformed into the form of WO3 on ZrMo2O8,and the experimental apparent dispersion thresholds became approximate to the monolayer dispersion capacities of WO3 and ZrMo2O8 on ZrO2. The results of measurements by Hammett indicator and n-pentane isomerization methods showed that Ho of the WO3/ZrO2 systems reached-13.8--14.5 and that of the MoO3/ZrO2 systems-12.0--12.7,and the samples containing the amounts of WO3 and MoO3 close to their monolayer dispersion capacities and calcined at 800℃ displayed stronger superacidity.
出处
《高等学校化学学报》
SCIE
EI
CAS
CSCD
北大核心
1995年第1期111-115,共5页
Chemical Journal of Chinese Universities
基金
国家基础研究重大项目
中国石油化学工业总公司发展基金
关键词
固体
超强酸
氧化钨
氧化锆
氧化钼
氧化锆
Solid superacid,WO3/ZrO2, MoO3/ZrO2,Characterization of acidity
