Journal of Molecular Catalysis A-Chemical, Vol.264, No.1-2, 170-178, 2007
In situ generation of Pd nanoparticles in MCM-41 and catalytic applications in liquid-phase alkyne hydrogenations
Pd-MCM-41 materials were synthetized by using the cationic surfactant tetradecyltrimethylammonium bromide (C(14)TABr) for both the stabilization of the Pd particles and the construction of the mesoporous structure of MCM-41. Two Pd-MCM-41 samples, for which the Pd particles were generated before and after formation of the MCM-41 framework (Pd-A and Pd-B, respectively), were investigated. Structural characterization of the samples was carried out by ICP-AES, N-2 Sorption, XRD and TEM measurements. It was established that the highly ordered structure of MCM-41 was not appreciably affected by the formation of the I'd particles. Further, a similar particle size control was achieved for both Pd-MCM samples. However, both the location and the size distribution of the I'd particles were found to depend strongly on the preparation procedure. For Pd-A, the Pd nanoparticles were essentially situated on the external surface of MCM-41, whereas for Pd-B, the particles were found to be encapsulated inside the mesopores. For the liquid-phase hydrogenations of alkynes, the catalytic activity of Pd-A clearly surpassed that of Pd-B, indicating that the external Pd crystallites were more readily accessible for the reactants than those incorporated in the MCM-41 framework. The limited activity observed for Pd-B was attributed to mass transport limitations due to diffusion of the reactants into the mesopores of the MCM-41 host. (c) 2006 Elsevier B.V. All rights reserved.