Catalytic benzylation of arenes using metal-ion modified HY zeolites for sustainable synthesis

Abstract

Microporous zeolites are commonly employed as catalysts for the benzylation of arenes and benzyl alcohol. However, their catalytic efficiency is often compromised by diffusion limitations, particularly in reactions involving larger arenes. In this study, we developed metal-ion modified HY zeolites using Zn, Mg, and Ni as dopants and investigated their catalytic performance in the benzylation of a range of arenes, including toluene, benzene, mesitylene, p-xylene and with benzyl alcohol (BzOH). The structural and acidic properties of the modified HY zeolites were characterized using a combination of techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂ adsorption–desorption isotherms, Fourier-transform infrared (FTIR) spectroscopy, ammonia temperature-programmed desorption (NH₃-TPD), and proton magic angle spinning nuclear magnetic resonance (¹H MAS NMR) spectroscopy. The presence of catalytically active Brønsted acid sites (BAS) was detected by 1H MAS NMR spectroscopy and it was demonstrated that the HY zeolite's acidity is considerably modulated by the addition of metal ions. The catalytic evaluations indicated that the metal-ion modified HY zeolites exhibited superior activity compared to unmodified HY zeolite, with the catalytic performance following the order Zn/HY > Ni/HY > Mg/HY > HY for the benzylation of benzyl alcohol with mesitylene. Further investigation into the mechanism revealed that the synergistic effect of metal ions and acidity plays a crucial role in enhancing the accessibility of arenes to the surface catalytic sites and thereby improving catalytic performance. These findings underscore the importance of the metal-acidity synergy in optimizing the catalytic efficacy of modified HY zeolites for selective benzylation reactions.