Zeolites are microporous, crystalline material with uniform molecular-sized pores ranging from 0.35 to 1.3 nm. Although there are more than 200 types of zeolites with different structures, pore size gap exists in the zeolite family. Our research in this direction is focused on fine-tuning the pore entrance sizes of zeolites by depositing ultrathin microporous coatings by molecular layer deposition (MLD), as shown schematically in Figure 1, to achieve effective separation of industrially important mixtures.
Under the support by NSF, DOE/ARPA-E and DOE/NETL, we obtained the following key results and reported them in peer-reviewed journals:
· We found 5A zeolite pore mouth size can be precisely controlled at a step change of ~0.01 nm by adjusting the thickness of the microporous Al2O3 thickness from 6 to 60 nm.
· Microporous TiO2 coating was shown to be able to reduce 5A zeolite pore size to be between CO2 and N2; the MLD modified 5A can effectively separate CO2 from N2 by size difference.
· Further adjusting 5A pore mouth size by combining MLD with atomic layer deposition (ALD) was shown to be able to effectively separate propylene from propane
MLD has shown its great potential for modifying the zeolite surface and thus precisely adjust pore mouth size. Surprisingly, we also found MLD can be used to modify the internal surface/cavity of some large pore zeolites to change the surface affinity to some molecules and segregate the large cavity into several smaller ones. This may open completely new field for zeolite applications in both adsorptive separation and catalysis. We will systematically study how MLD will change the internal surface of zeolites and explore the modified zeolites for catalysis and adsorptive separation.