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