高分散隔离活性位催化剂中过渡金属离子结构对丙烷选择氧化反应性能的影响

Catalytic Effect of Configuration Structures of Transition Metal Ions in Catalysts with Highly Dispersed and Isolated Active Sites on the Selective Oxidation of Propane

考察了碱金属K修饰的SiO2负载极低含量过渡金属的高分散隔离活性位系列催化剂(K-M/SiO2(n(K)∶n(M)∶n(Si)=10∶1∶1000),M=V,Cr,Mn,Fe,Co,Ni,Cu,Zn)的丙烷选择氧化催化性能,并运用UV-Raman和CO2-TPD等方法,对该系列催化剂进行了结构和物化性能表征,探讨了催化剂的表面离子结构与催化反应性能之间的关系。发现钾修饰的SiO2负载过渡金属高分散隔离活性位催化剂上过渡金属离子的组态结构,对丙烷选择氧化反应性能有重要影响。相对稳定的全充满或无d电子的表面离子结构有利于选择氧化反应进行,而存在多种价态的相对不稳定的离子结构有利于深度氧化的进行。这一离子结构与丙烷选择氧化催化性能的关系与前期乙烷选择氧化规律相似,进一步说明在高分散隔离活性位催化剂中,过渡金属离子的电子组态结构是影响低碳烷烃选择氧化反应性能的最重要因素。

The catalytic performances of the potassium-modified silica-supported catalysts with highly dispersed and isolated active sites containing a tiny amount of transition metal oxide （i. e. , K-M/SiO2 （n（ K）：n （M）： n （Si） = 10：1：1000） ; M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn） for the selective oxidation of propane were evaluated. The structures and physieo-chemical properties of these catalysts were characterized by means of UV-Raman, CO2-TPD. The relationships among the catalytic performances of this series of catalysts for the selective oxidation of propane and their configuration structures of the transition metal cations were studied. The results indicate that the configuration structures of transition metal cations have large effect on the catalytic performances of the catalysts for the selective oxidation of propane. The stable cation structures with d-orbitals, which are fully occupied or empty, are good for the selective oxygenation of propane. But the cations, which have the relatively unstable d-electron structures with mixed valences, are good for the deep oxidation of propane. This relation between the cation structures of highly dispersed and isolated active sites of the catalysts and their catalytic performances is very similar to that found in the selective oxidation of ethane, which further demonstrates that the configuration structures of transition metal cations in the catalysts with highly dispersed and isolated active sites is the most important controlling factor to affect the catalytic performances of this kind of catalysts for the selective oxidation of low alkanes.