MoO_3在Ga_2O_3上的分散研究

STUDY OF THE DISPERSION OF MoO_3 ON Ga_2O_3

采用ＸＲＤ， ＬＲＳ，ＦＴＩＲ， ＵＶＤＲＳ和ＴＰＲ 研究了ＭｏＯ３ 在载体Ｇａ２Ｏ３ 上的分散情况．结果表明： ＭｏＯ３ 的分散状态受Ｇａ２Ｏ３ 表面结构的影响， ＭｏＯ３ 在Ｇａ２Ｏ３ 上的分散容量约为８－４μｍｏｌ／ｍ２ ； 低于该分散容量时， Ｍｏ６ ＋ 主要以高分散态存在于Ｇａ２ Ｏ３ 表面，而高于该分散容量时，除有分散态的Ｍｏ—Ｏ 物种外，还有残余的ＭｏＯ３ 晶相出现．ＴＰＲ 结果表明： ＭｏＯ３ 低于分散容量时，体系中只观察到两个有关钼物种的还原峰（４００ ℃和８５０ ℃） ； 高于分散容量时， 又出现一个新还原峰（５５０ ℃） ．４００ ℃处的峰为分散态钼物种中的Ｍｏ６ ＋ 还原为Ｍｏ４ ＋ ；５５０ ℃处的峰为ＭｏＯ３ 晶相中的Ｍｏ６ ＋ 还原为Ｍｏ４ ＋ ；８５０ ℃处的峰为Ｍｏ４ ＋ 还原为Ｍｏ０ ． 结合嵌入模型对这些实验事实进行了解释．

XRD, LRS, FT IR, UV DRS and TPR were used to characterize the dispersion of MoO 3 on Ga 2O 3. The results showed that the dispersion capacity (defined as MoO 3 amount on unit surface area of Ga 2O 3) is 8 4 μmol/m 2 (corresponding to Mo 6+ of 5 04/nm 2). In the samples with MoO 3 loading lower than the dispersion capacity, MoO 3 highly dispersed on the surface of Ga 2O 3; while in the samples with MoO 3 loading higher than the dispersion capacity, the crystalline MoO 3 was also found besides the dispersed species. For the MoO 3/Ga 2O 3 samples with lower MoO 3 loading, there were two reduction peaks appearing at ca 400 ℃ and ca 850 ℃ in TPR profile, corresponding to the reduction of Mo 6+ to Mo 4+ and Mo 4+ to Mo 0 respectively. For the samples with higher MoO 3 loading, another peak at ca 550 ℃ appeared owing to the reduction of crystalline MoO 3.These results were discussed by the incorporation model proposed previously.