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

Alumina-based oxides Al2O3, Al2O3–ZrO2 (A, B, C) and Al2O3–ZrO2–Eu2O3 (D) were prepared by alkoxide sol–gel method and used as supports for palladium nanoparticles obtained by reduction of PdCl2 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 PdCl2 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 + H2O used as a solvent, KOH as a base), a Pd(0)/PVP colloid exhibited slightly lower catalytic activity.