间二甲苯氨氧化V-Cr-O系催化剂表面活性组分特征

CHARACTERISTICS OF ACTIVE SURFACE COMPONENTS OF V-Cr-O CATALYSTS USED FOR AMMOXIDATION OF m-XYLENE TO ISOPHTHALONITRILE

采用显微能谱 (SEM XRAS)和X 射线光电子能谱 (XPS)方法分析了V Cr O催化剂表面活性组分的组成及状态 ,并用程序升温还原 (TPR)方法考察了催化剂活性组分的还原特征。结果表明 ,Cr与V的摩尔比 (n(Cr)∶n(V) )依次增加的 3种催化剂样品VCB1、VCB2和VCM的表面均显示出Cr的富集。样品经 5 0 0℃处理2h后 ,催化剂VCB1和VCB2中V的结合能增大 ,Cr进一步向催化剂表面迁移 ;而催化剂VCM则保持表面状态的相对稳定。催化剂还原耗氢能力依VCB1、VCB2、VCM的顺序依次增强 ,其顺序与催化剂中n(Cr) :n(V)增大的顺序一致。VCM的表面脱 [H]能力较强 ,供 [O]能力较弱 。

The active component characteristics of the V-Cr-O catalysts were characterized by means of SEM-XRAS, XPS, and TPR. The results revealed that the molar ratio of active components Cr to V on surface phase is greater than that in the bulk, and element Cr moved to the catalyst surface in the process of catalyst preparation. After treated in air at 500°C for 2 h, bonding energies of element increased and Cr moved to the surface of catalysts VCB1 and VCB2, while the surface of VCM catalyst remained relatively stable. The ability of hydrogen consumption of catalysts increases according to the order of VCB1, VCB2 and VCM, and the same order for n(Cr): n(V) ratio in catalysts. For VCM catalyst, the ability of surface dehydrogenation from m-xylene is stronger and oxygen supply is weaker. It may be one of the reasons that lower molecular-mass components are produced during reaction on catalyst VCM.