Tailoring the physicochemical properties of zeolites through organic-free synthesis routes
Matthew D. Oleksiak and Jeffrey D. Rimer*
University of Houston, Department of Chemical and Biomolecular Engineering, 4800 Calhoun Rd, Houston, TX 77204
The unique acidity, thermal stability, and shape-selectivity of nanoporous zeolites are utilized in industrial applications spanning catalysis to ion exchange. Difficulties in the formation of zeolites in organic-free synthesis are prevalent, and the most common concern is the formation of undesirable crystal phase(s), i.e. impurities. Oftentimes, organic structure-directing agents (OSDAs) are used to achieve phase-pure crystals, though these additives are typically costly and must be removed by post-synthesis calcination. In order to both understand and control organic-free polymorphism, we constructed kinetic phase diagrams based on varying synthesis conditions using only inorganic ions (e.g., alkali metals) as the structure-directing agents.1 These kinetic diagrams serve as a platform for tailoring the physicochemical properties of zeolites.2 Notably, we were able to synthesize LTA and FAU crystals with much higher silicon-to-aluminum ratios (SARs) than conventional procedures without the use of an OSDA or post-synthesis modification (e.g., dealumination).3 To our knowledge, we have produced the highest silica containing LTA and FAU type zeolites reported in the literature using a cost-effective method that is capable of improving the thermal stability of these materials and allows for greater control of framework acidity. Additionally, we have been able to selectively tailor the properties of small-pore zeolites, such as the GIS framework type, and generate synthetic polymorphs of zeolites that are typically only found in nature. We have shown that these polymorphs differ in their thermal stability and exhibit properties that are ideal for selective separations of small molecules. Here, we will present the results of these studies along with a systematic investigation of early stage polymorph selection based on time-resolved analysis of zeolite precursor formation and their structural transformation(s) during hydrothermal treatment.
1. Maldonado, M., M.D. Oleksiak, S. Chinta, and J.D. Rimer, Controlling Crystal Polymorphism in Organic-Free Synthesis of Na-Zeolites. Journal of the American Chemical Society, 2013. 135(7): p. 2641-2652.
2. Rimer, J.D., M. Kumar, R. Li, A.I. Lupulescu, and M.D. Oleksiak, Tailoring the Physicochemical Properties of Zeolite Catalysts. Catalysis Science & Technology, 2014. 4: p. 3762-3771.
3. Conato, M.T., M.D. Oleksiak, B.P. McGrail, R.K. Motkuri, and J.D. Rimer, Framework Stabilization of Si-Rich LTA Zeolite Prepared in Organic-Free Media. Chemical Communications, 2015. 51: p. 269-272.
See more of this Group/Topical: Materials Engineering and Sciences Division