【摘要】 对P/V比在0.9-1.1间的七个VPO_x催化剂进行EPR谱和化学滴定测定。以VOSO₄为基准,求出单位EPR相对强度所代表的（VO）²⁺（％）。和化学滴定数据结合,得到催化剂中V³⁺,V⁴⁺和V⁵⁺离子的相对含量。从EPR谱图特征,将催化剂分成两类:一类为空气中焙烧而成,新鲜催化剂的V⁴⁺/V⁵⁺在0.7以上,V³⁺百分含量在9％以下。有宽而强,不对称的单—EPR峰轴讯号。反应后,△H_pp值增高,EPR强度下降。另一类为氮气中焙烧而成,新鲜催化剂的V⁴⁺/V⁵⁺在0.3以下,而V³⁺在22％以上,存在类似于“双峰”,实质上是宽化的,低分辨的V⁴⁺超精细结构（hfs）.hfs随P/V比下降而减弱,至P/V=0.9完全消失。该类催化剂反应后△H_pp值下降,而EPR强度增高。除了顺酐生成速率最高的一个催化剂外,其它六个催化剂上的顺酐生成速率基本上和催化剂中V⁴⁺/V⁵⁺比呈线性关系。更多还原

【Abstract】 EPR and chemical analysis were used to investigate the changes of oxidation numbers of Vanadium ions in seven VPO_x catalysts with P / V ratio of 0.9--1.1. VOSO₄ was applied as a standard of spin density. The percentage of （VO）²⁺ in VOSO₄ was determined by chemical analysis, and then the ratio of unit doubly integrated EPR signals of VOSO₄ and （VO）²⁺ （%） were obtained. The relative content of V³⁺, V⁴⁺, and V⁵⁺ ions in catalysts were also obtained by combination of EPR and chemical analysis. According to the characters of EPR signals, the catalysts were devided into two kinds. The V⁴⁺ / V⁵⁺ > 0.7, V³⁺ （%） < 9% were found for freshly calcined catalysts in air. They exhibited a broad but intense EPR signals. After reaction, the △H_pp increased, and EPR intensity decreased. But the other kind or freshly calcined catalysts in N₂ were quite different. The V⁴⁺ / V⁵⁺ < 0.3, V³⁺ （%） > 22% were found. A quasidouble peak EPR signal appeared. In fact, it was broadening, low resolution hyperfine structure due to the （VO）²⁺ （S= 1 / 2, I= 7 / 2） ions were apart from each other and dispersed both on the surface and in the bulk. The hfs was vanished, when P / V decreased to 0.9. In addition it should be noted that △H_pp decreased and EPR intensity increased after reac- tion. Besides, the linear relation was found between formation velocity of MA and ratio of V⁴⁺ / V⁵⁺ in catalysts apart from one best catalyst.更多还原