原位X射线衍射研究VO_x和MoO_x在Al_2O_3上的分散

In Situ X-Ray Diffraction Study of VO_x and MoO_x Dispersion on Al_2O_3

采用原位X射线衍射技术考察了机械研磨法和浸渍法制备的负载型VOx（MoOx）/Al2O3催化剂在空气中升温时的晶相变化. 结果表明,采用草酸络合浸渍法制备的VOx/Al2O3催化剂上前驱体（NH4）2[VO（C2O4）2]分散均匀,在升温至200～300 ℃时前驱体开始分解, 300～400 ℃是主要分解区间,到400 ℃时分解完全;VOx物种是通过晶相HxV2O5进行分散的. 机械研磨法制备的VOx/Al2O3催化剂在升温过程中虽然VOx与Al2O3之间存在相互作用,但并没有观察到明显的自发分散现象, V2O5一直以晶体氧化物形式存在. 在空气中升温至400 ℃时,浸渍法制备的MoOx/Al2O3催化剂上（NH4）6Mo2O24·4H2O已完全分解成MoO3. 机械研磨法制备的MoOx/Al2O3在加热过程中分解生成的MoO3与浸渍法得到的MoO3不完全相同,主要体现在（040）和（060）晶面的含量不同;机械研磨法制得的催化剂在500 ℃下焙烧1 h的分散度小于浸渍法制备的催化剂.

The dispersion of VO, and MoOx on Al2O3 was investigated by means of in situ X-ray diffraction. For the VOx/Al2O3 catalyst prepared by the impregnation method, the precursor of （NH4）2 [ VO（C2O4）2 ] dispersed uniformly on the support. （NH4）2[VO（C2O4）2] began to decompose at 200 ℃ , the decomposition finished at 400 ℃ , and the obtained VOx species dispersed through the HxV2O5 phase. For the VOx/Al2O3 catalyst prepared by mechanical grinding, although there was an interaction between V2O5 and Al2O3, no obvious spontaneous dispersion phenomenon was observed; thus the dispersion of VOx was rather poor as compared with the impregnated catalyst. For the MoOx/Al2O3 catalysts prepared by impregnation and mechanical grinding, the MoO3 phase resulted from （NH4）6Mo2O24·4H2O decomposition was not completely the same, and the contents of （040） and （060） crystal planes were different.