Phosphorous Moieties in P-ZSM-5 Zeolites

Phosphorus modified ZSM-5 (P-ZSM-5) zeolite was investigated using quantum mechanics density functional theory and our own N-layer integrated molecular orbital molecular mechanics method (ONIOM). Extra-framework phosphate and in-framework moieties containing phosphorus were found to be plausible local structures in P-ZSM-5 zeolites based on the calculated heats of formation and the free energy data from the hypothetical reactions. Furthermore, we find that the cationic moieties are favored at room temperature. The in-framework acidic moieties are more stable at high temperatures and the stability of the in-framework phosphorus moieties is insensitive to temperature changes. The calculated ²⁷Al, ³¹P, and ²⁹Si chemical shifts, acidity changes, and structural parameters agree well with the known experimental observations.