BEA/MOR两相共生分子筛的酸性及其催化性能  

Acidity and Catalytic Performance of BEA/MOR Intergrowth Zeolites

作　　者：祁晓岚[1] 李斌[1] 李士杰[1] 刘希尧[1] 林炳雄[1] 

机构地区：[1]北京大学化学与分子工程学院物理化学研究所

出　　处：《催化学报》2006年第3期228-232,共5页

基　　金：国家自然科学基金资助项目(20373002)

摘　　要：用NH3-TPD方法研究了相同硅铝比不同相组成的BEA/MOR(β沸石与丝光沸石两相共生分子筛)样品的酸性,并考察了其对甲醇脱水制二甲醚反应的催化性能.结果表明,不同相组成的共生分子筛样品的NH3-TPD谱中均出现两个NH3脱附峰,分别对应于NH3在沸石骨架中弱酸中心和强酸中心上的脱附.BEA/MOR的高温脱附峰温与其丝光沸石含量呈火山形曲线关系,而β沸石与丝光沸石机械混合物的高温脱附峰温与丝光沸石含量呈线性关系;当丝光沸石相含量超过50%时,BEA/MOR强酸强度明显高于机械混合物,含丝光沸石65%的BEA/MOR样品的强酸强度最强,这表明共生分子筛与机械混合物间存在明显的区别.用于催化甲醇脱水制二甲醚反应时,BEA/MOR样品上甲醇转化率与丝光沸石含量也呈火山形曲线关系,而机械混合物上甲醇的转化率与丝光沸石含量呈线性关系.丝光沸石含量超过40%的BEA/MOR样品的催化活性都高于HM,含丝光沸石65%的BEA/MOR样品活性最高.硅铝比为11的HM虽然初活性高,但反应60 h后即很快失活,而硅铝比为53的HBEA/MOR初活性稍低,但其稳定性好.The acid properties of BEA/MOR （intergrowth of zeolite β and mordenite） samples with SiO2/Al2O3 molar ratio of 25 were characterized by temperature-programmed desorption of NH3 （NH3-TPD）. There is a volcano-type relationship between the higher NH3-TPD peak temperature and the mordenite content of the BEA/ MOR samples, and the NH3-TPD peak temperature reached the maximum at mordenite content of about 65 %. In contrast, there is a linear relationship between the higher NH3-TPD peak temperature and the mordenite content of the mechanical mixtures of zeolite β and mordenite. No obvious difference in the acid strength existed between the BEA/MOR samples and the mechanical mixtures when the mordenite content was less than 50 %. However, when the mordenite content exceeded 50%, the BEA/MOR samples possessed much higher acid strength than the mechanical mixtures. The BEA/MOR sample with 65 % mordenite showed the highest acid strength, which was higher than that of the mordenite. The catalytic activity measurements of all the samples for methanol dehydration were carried out in a fixed-bed reactor under atmospheric pressure, temperature of 180 ℃, and methanol space velocity of 2 h^-1. Dimethyl ether and water were the only products for each catalyst. No coke formation and catalyst deactivation were observed in the reaction of 6 h. There is a linear relationship between the methanol conversion and the mordenite content of the mechanical mixtures. The BEA/MOR samples with mordenite content higher than 40% showed higher catalytic activity than HM, and the BEA/MOR with 65 % mordenite showed the highest methanol conversion. The catalytic activity of BEA/MOR also exhibited a volcano-type behavior. Compared with the mechanical mixtures, the BEA/MOR samples displayed higher catalytic activity. The HM with SiO2/Al2O3 molar ratio of 11 deactivated after 60 h reaction though it had high initial activity. The HBEA/MOR with SiO2/Al2O3 molar ratio of 53 showed relatively high catalytic activity and stability.

关 键 词：分子筛 Β沸石 丝光沸石 共生 酸性 氨 程序升温脱附 甲醇脱水 二甲醚 

分 类 号：O643.36[理学—物理化学]