Characterization of the acid sites in dealuminated nanosized HZSM-5 zeolite with the probe molecule trimethylphosphine

✍ Scribed by Weiping Zhang; Xiuwen Han; Xiumei Liu; Xinhe Bao

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 127 KB
• Volume: 194
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(02)00466-1

✦ Synopsis

The acid sites in dealuminated HZSM-5 zeolite with crystal sizes down to the nanoscale were firstly characterized by the probe molecule trimethylphosphine (TMP). As evidenced by the combination of 31 P CP/MAS NMR, 27 Al MAS and 1 H → 27 Al CP/MAS NMR measurements, the Brönsted acid sites of both microsized and nanosized HZSM-5 could be decreased upon the dealumination of zeolitic framework after hydrothermal treatment. At the same time, the appearance of Lewis acid sites was observed. The dealuminated nanosized HZSM-5 is easier to form Lewis acid sites than microsized HZSM-5, and the type of Lewis acid sites in nanosized HSM-5 is more than one. In addition, the origin of Lewis acid sites is mainly associated with the aluminum at ca. 30 ppm in the 27 Al MAS NMR spectra, and only a part of which in the dealuminated HZSM-5 zeolite acts as Lewis acid sites.