不同焙烧温度对Cu/γ-Al2O3催化剂铜物种结构的影响

用XRD和EXAFS研究了焙烧温度(35─1000 ℃)和负载量(质量分数为5－15％Cu)对于Cu/γ-Al_2O_3催化剂铜物种的影响。低于700 ℃焙烧时，铜以高分散状态存在。根据Cu~(2+)同时占据八面体(Oh)和四面体(Td)两种位置，对第一壳层的Cu-O配位峰进行了拟合。结果显示，随着焙烧温度增加，铜氧配位距离逐渐增加，Cu~(2+)(Oh)/Cu~(2+)(Td)的比例降低，并且Cu~(2+)(Oh)与氧的平均配位数从5.1变成6.0．这表明Cu~(2+)离子由Oh位向Td位迁移，同时向内层扩散使表面配位不饱和的氧缺顶畸变八面体部分变为配位饱和的对称八面体。900 ℃和更高温度的焙烧，使铜离子扩散进载体相形成CuAl_2O_4。

The Effect of Different Calcination Temperature on the Structure of Cu/γ-Al2O3 Catalysts

In this paper, the effects of calcination temperatures (350-1000 ℃) and metal loadings (5-15% Cu) on copper species of Cu/γ-Al_2O_3 catalysts are studied by means of XRD and EXAFS. For the catalysts, high dispersion state of the copper species could occur at calcination temperature below 700 ℃. The Cu-O coordination peaks at close to 0.16 nm were fitted according to Cu~(2+) taking octahedral (Oh) and tetrahedral (Td) sites. The results of two coordination shell fitting show that the average oxygen coordination numbers of Cu~(2+) (Oh) baries between 5.1 and 6.0. For 5CuY (Y: 350-700 ℃), the ratio of Cu~(2+) (Oh)/Cu~(2+) (Td) decreases gradually as calcination temperature increases, which means that Cu~(2+) ions in Oh move into Td site, and the coordination distance and average coordination number of Cu~(2+) (Oh) increase, indicating the Cu~(2+) (Oh) diffuse from open distorted Oh environment into symmetry one. As for 5Cu900, high temperature calcination makes Cu~(2+) ions diffusing into support phase, partly forming CuAl_2O_4. The value of Cu~(2+) (Oh)/Cu~(2+) ITd) is the same as that in CuAl_2O_4 at higher temperature (1000 ℃) or high loadings (10, 15% Cu).