Formation of ZSM-22 Zeolite Catalytic Particles by Fusion of Elementary Nanorods

• Published in: Chemistry : a European journal Vol. 13; no. 36; pp. 10070 - 10077
• Main Authors: Hayasaka, Kazuaki, Liang, Duoduo, Huybrechts, Ward, De Waele, Bart R., Houthoofd, Kristof J., Eloy, Pierre, Gaigneaux, Eric M., van Tendeloo, Gustaaf, Thybaut, Joris W., Marin, Guy B., Denayer, Joeri F. M., Baron, Gino V., Jacobs, Pierre A., Kirschhock, Christine E. A., Martens, Johan A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-01-2007; WILEY‐VCH Verlag
• Subjects: aggregation; aluminum; crystal growth; microporous materials; zeolites
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200700967

An ZSM‐22 aluminosilicate zeolite was synthesized using the hydrothermal gel method at 150 °C. Products obtained after different synthesis times were characterized using various techniques and catalytic testing. Massive formation of ZSM‐22 nanocrystals occurs after only a short synthesis time, appearing as isolated rods with a cross section of 12±4 nm. Nanorods have aluminum enriched at their external surface. Later in the crystallization process nanorods align and fuse sideways, whereby the external surface is systematically converted into an internal micropore surface. The formation of aluminum bearing micropores by the joining of nanorod surfaces is responsible for the enhanced catalytic activity. For this, the zeolite synthesis of nanoscale crystallites is ineffective for enhancing catalytic activity.
Elementary aluminum nanorods: Zeolite ZSM‐22 crystals are formed by sideways aggregation of nanorods. These grow along the direction of the micropores until the silicon source is used up. Aluminum preferably resides in the outer sides of the rods. Only after the nanorods aggregate (see figure) are the catalytically active sites formed in abundance. This is one example where nanosize is not superior for a catalytic application.