日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Suzuki-Miyaura coupling reaction was performed over the Pd/USY catalysts in which USY zeolites were prepared by steaming of NH₄-USY under various conditions. We found that the Pd/USY exhibited extremely high activity when bubbling with 6% H₂ were applied to the reaction before and during reactions. For instance, TON=13,000,000 was obtained in the reaction between bromobenzene and phenylboronic acid in 1.5 h. Pd/USY catalysts were applicable to the various kind of Suzuki-Miyaura reactions including naphthalene and chlorobenzene derivatives. Selection of an appropriate support (USY-zeolite), preparation condition of USY, solvent (o-xylene) and partial pressure of H₂ (6%) affected the catalytic activity of Pd to a great extent. Pd K- and L₃- edge XAFS analysis revealed the formation of atomic Pd with cationic character in o-xylene. Furthermore, catalytic activity of Pd/USY prepared under different steaming conditions was correlated with the strong Brønsted acid sites arisen from extra-framework Al, which was characterized by the peak appeared at 3598 cm^-1 in IR spectra. Based on these data, atomic Pd anchored on the strong Brønsted acid site of USY zeolite was proposed to be the active species.