(767e) Tuning the Physicochemical Properties of Growth Modifiers to Optimize Zeolite Catalysts

Authors: 
Kumar, M., University of Houston
Lupulescu, A. I., University of Houston
Rimer, J. D., University of Houston



There are growing opportunities for the use of zeolite catalysts in a wide range of applications. Despite their extensive use in commercial processes, an understanding of their growth mechanism(s) remains elusive. The rational design of zeolite catalysts calls for more versatile synthetic approaches capable of a prioritailoring crystal properties, such as crystal size, morphology, diffusion pathlength, and surface architecture. Here we will discuss the design of 1-D zeolites, notably LTL and MOR types, which commonly exhibit severe mass transport limitations due to their 1-D pores and suboptimal crystal habit. This class of porous materials offers an opportunity to explore the impact of crystal engineering on catalyst performance (i.e. activity and selectivity). To this end, we will discuss our studies of zeolite crystallization in the presence of zeolite growth modifiers (ZGMs), which are molecules that selectively bind to specific surfaces of zeolite crystals and mediate anisotropic growth rates [1]. We systematically examined a library of modifiers ranging in their structure and functional moieties to assess the physicochemical properties that regulate their efficacy and specificity as zeolite crystal growth modifiers. As we will demonstrate, the judicious selection of ZGMs can markedly alter zeolite crystal morphology from high aspect ratio (needle-like) crystals to thin discs with diffusion pathlengths and external surface areas that span more than 3 orders of magnitude. These studies revealed that ZGM hydrophobicity and the spatial sequencing of binding moieties are effective molecular descriptors of its efficacy [2]. Moreover, polymers proved to be more effective modifiers than their corresponding monomers. Collectively, these studies seek to establish a molecular screening method to provide general heuristics for designing 1-D zeolite structures. We will present these fundamental studies and also discuss how techniques, such as atomic force microscopy, can be used to probe the mechanisms of zeolite crystallization and the effects of ZGMs.

[1] Lupulescu, A.I. and Rimer, J.D., Angew. Chem. Int. Ed.51 (2012) 3345-3349.

[2] Lupulescu, A.I., Manjesh, K., Rimer, J.D., J. Am. Chem. Soc. 135 (2013) 6608-6617.