摘要
采用FT IR ,XRD ,BET ,TPD ,元素分析及孔结构和比表面积测试等手段研究了骨架外氧化铝存在的条件下 ,HF处理对Hβ沸石结构和酸性的影响 ,并提出了HF改性机理 .结果表明 ,在酸处理和氟化的双重影响下 ,桥形羟基 (36 0 5cm-1)、骨架外铝物种的羟基 (36 6 0cm-1)和不稳定骨架铝物种的高频羟基 (3782cm-1)逐渐减少 ,而链末端Si羟基 (3745cm-1)和羟基窝附近Si羟基 (3730cm-1)逐渐增多 .同时 ,随着处理程度的加深 ,β沸石的总酸量逐渐减少并趋于稳定 ,强弱酸比值逐渐增大 ,B酸量先降后升 ,L酸量逐渐下降 .但是 ,改性程度较深时 β沸石的酸性变化不大 .
The effect of HF treatment on the structure and acidity of β zeolite was investigated by XRD, BET, FT-IR, TPD and elementary analysis in the presence of extralattice Al 2O 3. It was found that the bridging hydroxyl ( 3?605 cm -1), OH bonded to extralattice aluminum ( 3?660 cm -1) and OH bonded to non-stated lattice aluminum ( 3?782 cm -1) gradually decreased and the internal Si-OH at framework defects ( 3?730 cm -1), and the terminal Si-OH ( 3?745 cm -1) gradually increased with the increase of fluorination time. Furthermore, the total acid amount gradually decreased and finally became constant, and the ratio of strong acid to weak acid gradually increased. The Brnsted acid sites decreasd at first and then increased, and the Lewis acid sites gradually decreased and the variation is insignificant as the increase of HF concentration. This is due to the double functions of hydrofluoric acid, which can provide not only proton for acid treatment but also fluorine for strong inductivity. Specially, when the samples were severely modified, the Brnsted acid sites were mainly due to the internal Si-OH at framework defects. The acidity of these sites came from the inductive effect of fluoride ions near them, and the acidity increased gradually with the introduction of more fluoride ions. These hydroxyl groups near to fluoride ions possess stronger acidity, resulting in the increase in the ratio of strong acid sites to weak acid sites.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2002年第4期371-375,共5页
