分子筛的酸处理对Mo/HZSM-5催化甲烷无氧芳构化反应性能的影响  

Effect of Acid Treatment of Zeolite on Catalytic Performance of Mo/HZSM-5 for Methane Dehydroaromatization

作　　者：刘红梅[1] 申文杰[1] 刘秀梅[1] 包信和[1] 徐奕德[1] 

机构地区：[1]中国科学院大连化学物理研究所催化基础国家重点实验室,辽宁大连116023

出　　处：《催化学报》2004年第9期688-692,共5页

基　　金：国家基础研究发展规划 ( 973计划 )项目 (G19990 2 2 40 6)

摘　　要：采用HNO3 溶液对HZSM 5分子筛进行预处理 ,并以处理后的分子筛为载体制备了Mo/HZSM 5催化剂 .结果表明 ,改性的Mo/HZSM 5催化剂在甲烷无氧脱氢芳构化反应中表现出很好的稳定性 ,显著地抑制了积炭物种在催化剂表面的形成 .SEM ,XRD和1HMASNMR等表征结果表明 ,酸处理在一定程度上降低了HZSM 5分子筛的结晶度 ,使部分Al物种脱离骨架结构 ,迁移到骨架外形成新的表面Al羟基 ,从而使HZSM 5分子筛上B酸中心的数目明显减少 .未经改性的Mo/HZSM 5催化剂表面 ,平均每个晶胞中有 1 12个B酸位 ,而改性的Mo/HZSM 5催化剂表面 ,平均每个晶胞中仅有 0 88个B酸位 .这表明过多的酸性位存留在催化剂上会引起积炭的生成 ,降低催化剂的稳定性 .The pretreatment with HNO 3 solution was applied to modify HZSM-5 zeolite, and the Mo/HZSM-5 catalyst prepared by using the modified HZSM-5 zeolite as support showed higher stability in methane dehydroaromatization than that prepared by using unmodified HZSM-5 zeolite. Meanwhile, the formation of coke was distinctly suppressed on the Mo catalyst supported on the modified HZSM-5 zeolite. The effect of acid treatment on the structure of HZSM-5 zeolite and Mo/HZSM-5 catalyst was studied by SEM, XRD and 1H MAS NMR techniques. The results suggested that the acid treatment of HZSM-5 led to an obvious dealumination and a decrease in the crystallinity of HZSM-5 zeolite. A part of Al species was extracted from the zeolite framework and formed extra-framework Al-OH groups, resulting in an evident decrease of the number of Brnsted acid sites remained on the zeolite surface. As demonstrated in the 1H MAS NMR experiment, the number of B acid sites per unit cell was 1 12 on the Mo/HZSM-5 catalyst prepared using unmodified zeolite as support, but it was only 0 88 on the Mo catalyst supported on modified HZSM-5 zeolite. The result indicated that too many B acid sites on the catalyst would cause severe coking and decrease the catalyst stability.

关 键 词：HZSM-5分子筛 甲烷 脱氢芳构化 酸处理 脱铝 

分 类 号：O643[理学—物理化学]