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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.
Credit: Andrew Beale.
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"Zeolites" might be an unknown word to many
non-scientists, but its meaning is everywhere around us: when we wash
our clothes, drive a car or walk in the streets. They are used in many
processes, such as the production of petrol, detergents or concrete.
They are inorganic porous material 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 they 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 ESRF took
place on a specially developed set up, and combined three different
techniques, namely X-ray absorption spectroscopy and small and wide
angle diffraction. They complemented these with additional data using
Raman spectroscopy. "We could look at each aspect of the
crystallization process for the first time ever", explains Andrew
Beale, one of the researchers, from Utrecht University (The
Netherlands).
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.
"These results are highly relevant to the debate on the mechanism of
zeolite formation", asserts Rutger A. Van Santen, a scientist from the
Schuit Institute of Catalysis (The Netherlands), in the Nature article. |
