(228e) Elucidating the Impact of Organic Structure Directing Agent Isomer Ratios on the Aluminum Distribution in SSZ-39

Despite their widespread use in industry, the mechanisms governing the synthesis of zeolite catalysts are still poorly understood. Prior research has established the ratio of cis to trans isomers in organic structure directing agents (OSDAs) used during the synthesis of Cu-SSZ-39 from faujacite can influence the copper uptake, the catalytic activity towards NOx reduction, and the aluminum distribution. We evaluate how altering the OSDA isomer, in the presence and absence of sodium changes the favorability of various aluminum pair distributions in SSZ-39, which will in turn influence the copper uptake and catalytic activity. Starting from 26 distinct distributions of aluminum pairs each pair was charge compensated by either two cis OSDAs, two trans OSDAs, one cis and one trans OSDA, one cis OSDA and a sodium atom, or a trans OSDA and a sodium atom. Placement of the OSDAs was initially done by placing the OSDAs oriented with their charge centers facing oxygen atoms adjacent to aluminum atoms. To evaluate alternative OSDA positions the NWPEsSe code was used to generate additional starting positions enabling us to be confident our results were not due to bias in OSDA positioning. Geometry optimizations were performed using Vienna Ab initio Simulation Package. Our initial results indicate the most favorable positions for aluminum pairs are in stacked six membered rings and locations where the aluminum atoms are in separate ring structures (Separate), the least favorable distributions are within the same eight membered ring (8MR). When one of the OSDAs is replaced with a sodium cation, eight membered ring structures become significantly more favorable. Within these trends the favorability of various aluminum distributions changes based on the charge compensating species, suggesting the differences in aluminum distribution observed experimentally can be explained by the OSDA isomer used in synthesis favoring certain distributions over others.