Palladium nanoparticles supported on alumina-based oxides as heterogeneous catalysts of the Suzuki–Miyaura reaction

Abstract

Alumina-based oxides Al 2O 3, Al 2O 3–ZrO 2 (A, B, C) and Al 2O 3–ZrO 2–Eu 2O 3 (D) were prepared by alkoxide sol–gel method and used as supports for palladium nanoparticles obtained by reduction of PdCl 2 by methanol or hydrazine. As confirmed by XRD and TEM methods, such catalysts are composed of palladium nanoparticles well dispersed on the surface of the alumina matrix. The Suzuki coupling of 2-bromotoluene with phenylboronic acid, used as the test reaction, revealed that the obtained catalysts were quite efficient even at 40 °C and that their catalytic activity increased at 60 and 80 °C. Very good results (95% yield after 1 h) also were obtained when PdCl 2 supported on mixed oxides was used without earlier palladium reduction. It was confirmed that under the reaction conditions, Pd(0) nanoparticles of ca. 5 nm in diameter were formed on the support. Under the same conditions ( iPrOH + H 2O used as a solvent, KOH as a base), a Pd(0)/PVP colloid exhibited slightly lower catalytic activity.