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.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
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)
关键词
HZSM-5分子筛
甲烷
脱氢芳构化
酸处理
脱铝
molybdenum, HZSM-5 zeolite, methane, dehydroaromatization, acid treatment, dealumination
