Synthesis of High-Silica Erionite Driven by Computational Screening of Hypothetical Zeolites

A hypothetical zeolite framework was selected from a database of hypothetical structures and adapted based on the structural features relevant for deNOx and MTO catalysis. To attempt the realization of this structure, a computational energy-based approach was applied to select relevant organic structure directing agent (OSDA) molecules with large OSDA-zeolite stabilization energies, leading to the selection of three OSDAs (OSDA1, OSDA2, and OSDA3) as potential candidates for the synthesis of the hypothetical zeolite (Hypo#1). Instead of Hypo#1, erionite (ERI) was found to dominate the experimental product outcome when potassium was used as a mineralizing agent. In the case of OSDA3, a novel high-silica ERI was found. The different ERI products were characterized, intergrowth structures ruled out, and special attention was paid to the compositional and morphological features arising from the use of the different OSDAs. In the specific high-Si product obtained using OSDA3, a distinct tubular to prismatic crystal morphology could be seen. Theoretical stabilization energies calculated for potentially competing phases (Hypo#1, ERI, offretite (OFF), and chabazite (CHA) among others) could be used to rationalize the experimental outcome to a certain extent, but our results also show that only considering zeolite-OSDA interaction is probably not sufficient to realize hypothetical frameworks, especially for Al-containing zeolites where alkali ions play an important role during crystallization.