Atomic-level insights into the role of Ti–M in the structure, stability, and acidity of M-TS-1 catalysts (M = B, Al, Ga, Zr, and Sn)

Abstract

The incorporation of specific heteroatoms into titanium silicalite-1 (TS-1) can lead to its promising catalytic performance in the single-step conversion of ethylene to ethylene glycol, where the local environment of catalytic sites can critically govern the reactivity. In this study, density functional theory calculations were employed to investigate the incorporation preferences, stability, and acid properties (Lewis/Brønsted) of trivalent (M³⁺: B, Al, and Ga) and tetravalent (M⁴⁺: Zr and Sn) heteroatoms incorporated into an MFI framework alongside Ti (M-TS-1). Theoretical results revealed that Ti and B have thermodynamically distinct preferential sites, eliminating their competition in the location of the catalytic site, while Al, Ga, Zr, and Sn competed with the Ti for framework location. Notably, DFT calculations predicted that Sn, B, and Zr incorporation enhanced the Ti–OH defect formation, while the thermodynamic favorability of Si vacancy generation increased in M-TS-1 compared with that in TS-1. Furthermore, the introduction of heteroatoms was found to increase the acidity of TS-1, influencing its performance in acid-catalyzed reactions. Experimental studies supplemented the computational findings, confirming the predicted trends in location and acidity. Thus, this study provides a fundamental understanding of the structure and acidity of the heteroatom-doped TS-1, providing theoretical guidance for the targeted optimization of TS-1 for its improved catalytic performance.