Copper(II)- and palladium(II)-modified molecular sieve, a reusable catalyst for the Suzuki-Miyaura-coupling
Résumé
Copper-palladium bimetallic catalysts supported on 4 angstrom molecular sieve were prepared with two step impregnation (TSI) and co-impregnation (CI). These materials were studied to determine the importance of the preparation method, the interaction between the Cu-Pd particles, the activity, selectivity and stability in Suzuki-Miyaura reaction. The key-role of the preparation method in the composition of the metal species on the surface of the support was pointed out with catalyst characterisation methods (ICP, BET, XRD, TEM, EDS and TPR). The relationship between the properties of surface material and the catalytic performance and stability were examined too. The two metals (Cu, Pd) were brought to close interaction on the surface of the support. A correlation between these interactions and improvement of stability were found and proven with surface analysis methods. We found that a Cu-Pd alloy with atom ratio 1:1 is responsible for the catalytic activity. Our catalyst TSI was active and selective during six catalytic cycles in Suzuki coupling, whilst the activity of the catalyst prepared with CI dropped after the sixth use. This loss was due to the absence of Cu-Pd 1:1 alloy and the growth of the particle size.