Brønsted and Lewis Acid Sites in Dealuminated ZSM-12 and β Zeolites Characterized by NH3-STPD, FT-IR, and MAS NMR Spectroscopy
Brønsted and Lewis Acid Sites in Dealuminated ZSM-12 and β Zeolites Characterized by NH3-STPD, FT-IR, and MAS NMR Spectroscopy
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DOI：
10.1021/jp993072p
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发表时间：
2000-04
影响因子：
3.3
通讯作者：
Wenmin Zhang;P. Smirniotis;and M. Gangoda;R. Bose
中科院分区：
文献类型：
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作者：
Wenmin Zhang;P. Smirniotis;and M. Gangoda;R. Bose
采用红外光谱、核磁共振和NH_3分步程序升温脱附（STPD）等方法研究了脱铝ZSM-12和β沸石在较宽硅铝比范围内的酸性特征。对于所有样本，STPD实验显示存在五个不同的峰。由STPD实验得到的样品中铝原子与氨原子的比例为1：1，表明该技术可以准确地探测Si/Al ≥ 20的沸石的所有酸中心。FT-IR峰的仔细解卷积表明，只有合成的ZSM-12样品具有少量的刘易斯酸中心。我们发现，当温度升高到150 °C以上时，氨从这些刘易斯位点完全解吸。值得注意的是，所有脱铝ZSM-12样品都不具有任何刘易斯酸位点。这与通常已知的情况相反，因为在脱铝期间，骨架铝原子移动到骨架外位置。我...
Infrared spectroscopy, nuclear magnetic resonance, and NH3-stepwise temperature-programmed desorption (STPD) were used to study the acidity characteristics of dealuminated ZSM-12 and β zeolites in a wide range of Si/Al ratios. For all samples, the STPD experiments revealed the presence of five distinct peaks. A 1:1 relation between the Al atoms of each sample and ammonia determined from the STPD experiments was derived, thus indicating that this technique can probe accurately all acid sites for zeolites with Si/Al ≥ about 20. A careful deconvolution of the FT-IR peaks indicated that only the as-synthesized ZSM-12 sample possessed a small number of Lewis acid sites. We found that ammonia desorbs completely from those Lewis sites upon an increase of temperature above 150 °C. It is remarkable to note that all the dealuminated ZSM-12 samples do not possess any Lewis acid sites. This is in contrast to what is commonly known since during dealumination framework aluminun atoms move to extraframework locations. I...