Understanding How Zeolites Organize Themselves

10 December 2006

The growth of a zeolite. When an organic base is added to the gel, it acts as a template for the construction of the zeolite (upper row). However, when zinc is added into the gel, the organic base takes a different shape, leading to a different construction of the zeolite. Credits: Andrew Beale.

Scientists from the Netherlands, United Kingdom and the European Synchrotron Radiation Facility (ESRF) have just shed new light on how zeolites organize themselves when they are created. Zeolites are used in many chemical processes, such as the production of gasoline.

Zeolites are inorganic porous materials with a highly regular structure of channels and pores that allow some molecules to pass through, and cause others to be either excluded, or broken down. In nature, they are made of volcanic rock, but industry has been synthesizing them for many years.

In industry, zeolites are formed from a gel and only become catalysts or porous solids when templates are used to direct the formation of a structure. If organic bases (chemical compounds which can neutralize an acid) are added to the reaction, new structures can be formed, but the way this happens is not well understood. A deeper knowledge of this process would enable better catalysts to be made.

In order to get new insight on this process, the team of researchers from The Netherlands, United Kingdom and the ESRF monitored the synthesis of zeolites with organic bases in real time. They added zinc to the original gel because it promotes the formation of zeolites at low temperatures. They realized that this element influenced the template of the zeolite and the crystallization process. The results suggest that molecular organization of the zeolites occurs before crystallization, therefore, before the formation of zeolite crystals.

The time-resolved experiments at the beamline BM26A took place on a specially developed set up, and combined three different techniques: X-ray absorption spectroscopy and small- and wide-angle diffraction. They complemented these with additional data using Raman spectroscopy.

The new results may not have an immediate repercussion among industrial zeolite manufacturers, but they provide a new vision on these materials for the academic community. The outcome of this research was published in two papers in the Journal of American Chemical Society and has been recently reported in Nature.

Resources:

• “A Combined SAXS/WAXS/XAFS Setup Capable of Observing Concurrent Changes Across the Nano-to-Micrometer Size Range in Inorganic Solid Crystallization Processes”; Andrew M. Beale, Ad M. J. van der Eerden, Simon D. M. Jacques, Olivier Leynaud, Matthew G. O’Brien, Florian Meneau, Sergei Nikitenko, Wim Bras, and Bert M. Weckhuysen; J. Am. Chem. Soc., 128 (38), 12386 -12387, 2006. 10.1021/ja062580r S0002-7863(06)02580-7

• “Unique Organic-Inorganic Interactions Leading to a Structure-Directed Microporous Aluminophosphate Crystallization as Observed with in situ Raman Spectroscopy”; Matthew G. O'Brien, Andrew M. Beale, C. Richard A. Catlow, and Bert M. Weckhuysen; J. Am. Chem. Soc., 128 (36), 11744 -11745, 2006. 10.1021/ja064230a S0002-7863(06)04230-2

• “Porous solids get organized”; Rutger A. van Santen; Nature 444, 46 - 47 (02 Nov 2006)