摘要
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-Al2O3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Cu2+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，Cu2+（Oh）／Cu2+（Td）的比例降低，并且Cu2+（Oh）与氧的平均配位数从5．1变成6．0．这表明Cu2+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CuAl2O4。
In this paper, the effects of calcination temperatures (350-1000 ℃) and metal loadings (5-15% Cu) on copper species of Cu/γ-Al2O3 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 0.16nm were fitted according to Cu2+ taking octahedral (Oh) and tetrahedral (Td) sites.The results of two coordination shell fitting show that the average oxygen coordinationnumbers of Cu2+ (Oh) varies between 5.1 and 6.0. For 5CuY (Y: 350-700 ℃), the ratio of Cu2+ (Oh)/Cu2+ (Td) decreases gradually as calcination temperature increases, which means that Cu2+ ions in Oh move into Td site, and the coordination distance and average coordination number of Cu2+ (Oh) increase, indicating the Cu2+ (Oh) diffuse from open distorted Oh environment into symmetry one. As for 5Cu900, high temperature calcination makes Cu2+ ions diffusing into support phase, partly forming CuAl2O4. The value of Cu2+ (Oh)/Cu2+ (Td) is the same as that in CuAl2O4 at higher temperature (100℃)or high loadings (10, 15% Cu).
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
1994年第7期623-627,共5页
Acta Physico-Chimica Sinica
基金
国家自然科学基金
关键词
铜基氧化物
焙烧
催化剂
铜物种
Cu/γ-Al_2O_3 catalyst, Calcination temperature, EXAFS
