Bimetallic Co-Pd catalysts: Study of preparation methods and their influence on the selective hydrogenation of acetylene
Aiming at the preparation of catalysts with well-controlled structure and composition, bimetallic CoPd nanoparticles (NPs) were prepared in two different ways using polyol methods. In the first case, support materials, such as active carbon, MgO and gamma-Al2O3, were present during synthesis, resulting in the formation of the particles directly on the surface of the supports. In the second case, functionalized NPs were first prepared in colloidal solution, using Poly(N-vinyl-pyrrolidone) (PVP) as stabilizing agent, and then deposited on the same support materials as above. All samples were characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). For the first approach, the data revealed that the support material plays an important role for the formation and chemical composition of the NPs. On the contrary, for the second approach, TEM images showed CoPd NPs of homogeneous composition and with a narrow size distribution on the supports. The bimetallic NPs were spherically shaped (d = 3.0 +/- 0.4 nm), whereas the monometallic counterparts were inhomogeneously dispersed with larger sizes and irregular shapes. According to EDX and atomic absorption spectroscopy, the atomic Co/Pd ratio for the bimetallic NPs was similar to 1:1 in agreement with the Co/Pd ratio adjusted during synthesis. The polymer matrix could be successfully removed simply by pyrolysis of the polymer carried out at 400 degrees C under H-2 for 30 min. Comparison of both preparation approaches shows a high potential of the colloidal bimetallic NPs for the use as supported metal catalysts because systematic control over structure and composition can be achieved as compared to such preparation methods where the support is already present during the synthesis. The higher activity and selectivity of catalysts prepared in this way could be proven by the selective hydrogenation of acetylene.