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, Sn)

Abstract

The distribution of Ti and co-incorporated heteroatoms within the zeolite framework governs their catalytic efficiency for single-step ethylene to ethylene glycol conversion. 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 the MFI framework alongside Ti (M-TS-1). Theoretical results revealed that Ti and B exhibit distinct preferential site thermodynamically, eliminating competition in catalytic site location, whereas Al, Ga, Zr, and Sn may compete with Ti for framework location. Notably, DFT calculations predicted that Sn, B, and Zr incorporation enhances Ti-OH defect formation, while the thermodynamic favorability of Si vacancy generation in M-TS-1 increases compared to TS-1. Furthermore, the introduction of heteroatoms was found to increase the acidity of TS-1, influencing its performance in acid-catalyzed reactions. Experimental validation supplemented the computational findings, confirming the predicted trends in location and acidity. This study provides a fundamental understanding of the structure and acidity of heteroatom-doped TS-1, providing theoretical guidance for the targeted optimization of TS-1 for improved catalytic performance.