PNNL

Abstract

This work integrates experiments and computational methods to quantify how the cis/trans ratio of the OSDA used in SSZ-39 synthesis impacts the crystallization kinetics, material properties, and final product composition. The crystallization kinetics increase by 30% when increasing the trans isomer content from 14% to 80%. Per prior work, in all cases based on the synthesis gel composition and product yield aluminum is the limiting reagent, and the absence of any amorphous material detected in the time resolved PXRD studies leads us to conclude that FAU dissolution is the rate limiting step in the formation of SSZ-39 in this synthesis protocol. The NMR binding studies, and corresponding DFT-based results show that the trans isomer binds to FAU more strongly than the cis isomer, providing one possible explanation for this nhancement in kinetics. The TGA and NMR results suggest that the trans isomer of OSDA is selectively incorporated into the product. The EDS analysis indicates that the Si/Al ratios are between 7.7 and 8.6 at low and high trans OSDA content, indicating zeolite composition is mildly sensitive to the trans isomer content. EDS results show this decrease in aluminum content leads to a corresponding decrease in sodium uptake. DFT-based calculations confirm OSDA-sodium interactions cannot explain any decrease in sodium uptake, reinforcing lower aluminum content as the cause of lower sodium uptake. The authors acknowledge NSF grant CBET-2035302 and CBET-2035280 for support. C. U. also acknowledges partial funding from the CeRCaS NSF IUCRC under grant number CBET-1939876. The authors thank Dr. Jeewan Pokhrel for the SEM images. This work was partially funded by the Joint Center for Deployment and Research in Earth Abundant Materials (JCDREAM) in Washington State. This work also used Bridges-2 at the Pittsburgh Supercomputer Center through allocation CHE170068 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program[35], which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296. Additional computational resources were provided by the Kamiak HPC under the Center for Institutional Research Computing at Washington State University. We also thank the Kulkarni group for fruitful discussions. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. DOE.