Abstract: The acid properties of Bronsted acid (B acid) sites in molecular sieves are key factors influencing their catalytic performance. Using H-modified EUO-structure molecular sieve (HEUO molecular sieve) with a silica-to-alumina ratio [n（SiO₂）/n（Al₂O₃）] of 110 as a model system, the acid strength, structural characteristics, and electronic properties of B acid sites in HEUO molecular sieve were investigated using the density functional theory (DFT) calculation method. The results indicate that the T7 site is the most favorable position for Al atom substitution, and B acid sites within the channels exhibit similar acid strengths and structural properties. The B acid site at the T5 position is influenced by surrounding framework oxygen atoms, leading to an elongated O—H bond, an increased Si—O—Al bond angle, enhanced positive charge on the H atom, and reduced negative charge on the O atom. Orbital analysis reveals that the HOMO orbital energy at the B9 site is significantly higher than that of other B acid sites, resulting in a smaller HOMO-LUMO energy gap compared to other sites. This work elucidates the intrinsic characteristics of B acid sites in HEUO molecular sieve at the quantum-chemical level, providing theoretical insights into their acid properties.

Key words: HEUO molecular sieve, density functional theory, structural characteristics, electronic properties