Effects of F/Nb mol ratio of F-Nb/HZSM-5 catalyst on the catalytic performance for ethanol dehydration to ethylene
-
摘要: 利用BET、NH3-TPD、FT-IR、MAS-NMR和SEM等方法研究了经不同F/Nb负载的F-Nb/HZSM-5催化剂的结构和表面酸性，并与乙醇催化脱水制乙烯的反应催化性能进行了关联。结果表明，F-Nb改性后的HZSM-5分子筛发生了明显的脱铝现象，且随着F离子添加量的增加，脱铝越发严重。经 27Al MAS NMR测试显示，脱铝后产生了新的非骨架铝物种，其化学位移为-13.5。随F/Nb摩尔比的增大，改性HZSM-5的弱酸、强酸量都减少。当F/Nb摩尔比大于2时，NH3-TPD谱中观察到在500 ℃的高温区出现新的酸性位。当F/Nb摩尔比为0.7时，F-Nb/HZSM-5催化剂催化低浓度乙醇脱水制乙烯性能得到改善，转化率、选择性和产率均达到最高，且优于HZSM-5分子筛，F/Nb的添加有效延长了催化剂的稳定性。Abstract: The structures and surface acidities of F-Nb/HZSM-5 catalysts with different F/Nb mol ratio were studied using BET, NH3-TPD, FT-IR, MAS-NMR and SEM. The catalytic performance of these catalysts for ethanol dehydration to ethylene was evaluated and correlated with the characterization results. It is found that, dealumination of HZSM-5 occurred after modification and the depth of dealumination increased with the increase of the amount of F added. The extra-framework aluminum species were observed by 27Al MAS NMR with a signal appeared at -13.5. With the increase of F/Nb mol ratio, both weak and strong acid amounts decreased and a new strong acid site was found in the NH3-TPD profile at 500℃. The catalyst with F/Nb mol ratio of 0.7 gave the highest catalytic activity and selectivity. The stability of the catalyst was greatly improved by the addition of F-Nb.
-
Key words:
- niobium oxide /
- ammonium fluoride /
- HZSM-5 molecular sieve /
- solid acid catalyst /
- ethanol /
- ethylene /
- dehydration
-
点击查看大图
计量
- 文章访问数: 1349
- HTML全文浏览量: 13
- PDF下载量: 681
- 被引次数: 0
下载:
