Tailored Catalytic Properties of MFI-Type Zeolite Through Controlled Surface Modifications: Theory, Synthesis and Catalytic Testing

Tailored Catalytic Properties of MFI-Type Zeolite through Controlled Surface Modifications: Theory, Synthesis and Catalytic Testing

Arian Ghorbanpour, Lars C. Grabow, and Jeffrey D. Rimer

University of Houston, Department of Chemical and Biomolecular Engineering,

4800 Calhoun Rd., Houston, TX 77004

Nanoporous zeolites are utilized in many industrial processes because of their superior thermal stability, tunable acidity, and shape-selectivity. Notably, the aluminosilicate MFI-type zeolite (termed ZSM-5) is active for various reactions. Much attention has been given to the activity and identity of catalytic sites within the interior pores; however, active sites located on the external surfaces of zeolite catalysts may be equally, if not more, important. Although the shape-selectivity effect in zeolite catalysis has been investigated ^1,2, differences between the inner and outer surface activity of zeolite catalysts are not well understood, which necessitates increased research thrusts to develop an improved fundamental knowledge of the active site(s). To this end, we have synthesized core-shell MFI-type zeolites composed of an active (ZSM-5) core and a non-active shell of silicalite-1 (siliceous analogue of ZSM-5) with 5 – 10 nm thickness. The "passivation" of external active sites with this thin silica layer helps to distinguish differences in the intrinsic activity of internal and external sites. Here, we will discuss results from catalyst synthesis, testing, and computational modeling using density functional theory (DFT) to calculate the stability of bulk and surface acidic sites and to model reaction kinetics. Proper catalytic tests are carried out to compare the performance of our core-shell materials with that of ZSM-5. This unique combination of synthesis, testing and modeling represents a synergistic approach in rational catalyst design that allows us to develop structure-function relationships in zeolite catalysis.

References:

¹ D.V. Vu, M. Miyamoto, N. Nishiyama, Y. Egashira, K. Ueyama, J. Catal. 243 (2006) 389-394.

² Y-J. Ji, B. Zhang, L. Xu, H. Wu, H. Peng, L. Chen, Y. Liu, P. Wu, J. Catal. 283 (2011) 168-177.