Temperature Effect on 1H Chemical Shift of Hydroxyl Groups in Zeolites and Their Catalytic Activities as Solid Acids
Temperature Effect on 1H Chemical Shift of Hydroxyl Groups in Zeolites and Their Catalytic Activities as Solid Acids
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DOI：
10.1021/jp3043945
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发表时间：
2012-07-12
影响因子：
3.7
通讯作者：
Baba, Toshihide
中科院分区：
文献类型：
--
作者：
Munakata, Hajime;Koyama, To-ru;Baba, Toshihide
用变温H-1魔角旋转核磁共振（H-1 MASNMR）技术研究了298 ~ 673 K温度范围内不同类型沸石（ZSM-5型沸石，包括硅沸石、丝光沸石和Y型沸石）H+交换后的H-1化学位移随温度的变化规律。由于桥连羟基（Si-（OH）-Al，布朗斯台德酸位点），其具有较低的质子跳跃活化能，末端硅烷醇基团和巢状硅烷醇基团的H-1化学位移随温度增加。由于桥接羟基基团的H-1化学位移的温度依赖性比由于末端硅烷醇基团和嵌套硅烷醇基团更明显。本文根据沸石变温H-1 MAS NMR测量结果、NH_3程序升温脱附测定的NH_3吸附热等热分析数据以及催化剂对乙醇和1-己烯转化的活性，讨论了分子筛中羟基酸强度与H-1化学位移的关系。结果表明，硅沸石分子筛上的巢状硅醇基团具有Bronsted酸中心的作用，在673 K时可催化乙醇和1-己烯的转化，其催化活性与B-ZSM-5分子筛上的桥羟基相当。
The influence of temperature on the H-1 chemical shift due to hydroxyl groups in H+-exchanged any kind of zeolites (ZSM-5 type zeolites including silicalite, mordenite and Y zeolites) was examined by variable temperature H-1 magic-angle spinning nuclear magnetic resonance (H-1 MAS NMR) spectroscopy measured from 298 to 673 K. The H-1 chemical shifts due to bridging hydroxyl groups (Si-(OH)-Al, Bronsted acid sites), which have a lower activation energy for proton jumping, terminal silanol groups, and nest silanol groups increased with temperature. The temperature dependence of the H-1 chemical shift due to the bridging hydroxyl groups was more pronounced than that due to the terminal silanol groups and also the nest silanol groups. The relationship between the H-1 chemical shift and the acid strength of the hydroxyl groups in zeolites was discussed on the basis of the variable temperature H-1 MAS NMR measurements of zeolites, previously reported thermal analysis data, such as the heat of NH3 adsorption measured by NH3 temperature programmed desorption, and also the catalytic activity for the conversion of ethanol and 1-hexene. It was found that the nest silanol groups of silicalite functioned as Bronsted acid sites and could catalyze the conversion of ethanol and 1-hexene with the same activity as the bridging hydroxyl groups in B-ZSM-5 at 673 K.