(684a) Tailoring the Morphology and Structure of Zeolite Catalysts Through the Use of Molecular Modifiers

Properties
such as exceptional thermal stability, unique shape-selectivity, and high
acidity place zeolites among the most frequently used industrial catalysts. The
inability to a priori control single
crystal growth, however, often yields materials with limited catalytic
performance due to long, tortuous internal diffusion pathlengths, as well as restricted
access to surface active sites. Rational design approaches capable of
selectively tailoring zeolite morphology and structure can dramatically improve
catalyst activity and lifetime ^1,2; and given the potential
application of zeolite catalysts for alternative fuels production (e.g.
biofuels) and mobile emissions technologies, there exists a critical need to expand
fundamental understanding of zeolite growth as well as robust design schemes
for optimizing zeolite catalysts. We will present a novel synthesis technique
that draws inspiration from nature wherein molecular modifiers are employed to mediate
anisotropic growth rates of zeolite crystals ³. By selectively
tuning modifier-zeolite molecular recognition, we can achieve remarkable
control of crystal morphology, size, and surface architecture. This versatile,
facile approach was used to synthesize several zeolite framework types. Results
of these studies will be discussed, highlighting the influence of molecular
modifiers on zeolite aspect ratio and surface area. In addition, we will
discuss interfacial studies that employ scanning probe microscopy to monitor
real time in situ growth of zeolites in actual reaction conditions. These studies
reveal interesting trends in step density, surface defects and growth
mechanisms, and growth kinetics in the presence of molecular modifiers.

[1] Choi, M., Na,
K., Kim, J., Sakamoto, Y., Terasaki O., Ryoo, R.,
Nature 461 (2009)
246-249

[2] Corma, A., J. Catalysis 216 (2003) 298-312

[3] Rimer, J.D.,
An, Z., Zhu, Z., Lee, M.H., Goldfarb, D.S., Wesson, J.A., Ward, M.D., Science

 330 (2010)
337-341