【摘要】 采用程序升温氮化的方法制备了分子筛负载的钼氮化物催化剂,并用EXAFS方法研究了氮化前后Mo原子的局域配位情况.氮化前负载MoO₃样品的径向结构函数中有三个峰,其中前两个峰对应着最近的Mo-O配位壳层,但是第一个峰与第二个峰的比例比晶体MoO₃中的比例大很多,表明分子筛负载的MoO₃具有更紧密的结构.氮化以后,Mo₂N样品的径向结构函数中有三个峰,对应于一个Mo－N和两个Mo－Mo配位壳层,与面心立方模型符合得很好.根据XRD和EXAFS谱的计算表明,Mo₂N中的N原子使Mo－Mo键拉长并削弱.分子筛负载的Mo2N样品具有与非负载Mo₂N样品近似相同的径向结构函数,只是对应于Mo－N壳层的峰较弱,表明负载的Mo₂N具有更大的结构无序性.更多还原

【Abstract】 Zeolites supported Mo nitrides were prepared via MoO₃＋NH₃ reaction in temperature programmed mannar.The XRD data show that the frame structure of NaY and Na-ZSM-5 zeolites can still be maintained after nitridation at 973K.By analysis of the extended X-ray absorption fine structure（EXAFS） of the Mo K-absorption edge,the structural informations of both oxidic and nitrided Mo catalysts were obtained.The supported MoO₃ samples show three peaks in the radial structure function（RSF）.The first two peaks correspond to the nearest Mo－O coordination shell,but the ratio of the first peak to the second one is much larger than that of the MoO₃.This suggests that the MoO₃ supported on zeolites has more compact structure than the unsupported one.There are three peaks in the RSF of Mo₂N,representing one Mo－N and two Mo－Mo shells,which is in good agreement with the face-centered cubic model.Calculation from X-ray diffraction data and EXAFS spectra reveals that the N atoms in Mo₂N lengthen the distance between Mo atoms and weaken the Mo－Mo bond.Supported Mo₂N samples give out nearly the same RSFs as the Mo₂N,only the peak corresponding to Mo－N shell is weak,suggesting that the supported Mo₂N has more structural disorder than the unsupported one.Mo₂N supported on Na-ZSM-5 gives out shorter coordination distance than supported on NaY,suggesting stronger interaction between Mo₂N and Na-ZSM-5.更多还原