Preparation, Characterization and Catalytic Activity of Palladium Nanoparticles Encapsulated in SBA-15
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Preparation, Characterization and Catalytic Activity of Palladium Nanoparticles Encapsulated in SBA-15 Changli Li Æ Qinghong Zhang Æ Ye Wang Æ Huilin Wan
Received: 12 August 2007 / Accepted: 30 August 2007 / Published online: 15 September 2007 Springer Science+Business Media, LLC 2007
Abstract A simple adsorption method was studied for the preparation of SBA-15-encapsulated palladium nanoparticles. This method employed the SBA-15 with organic template removed by ethanol extraction for the adsorption of cationic Pd precursors in alkaline solution followed by calcination and H2 reduction. The pH of the solution was found to be a critical factor in determining the palladium content and the ordered mesoporous structure. Our characterizations revealed that the Pd nanoparticles prepared by this method were located inside the mesoporous channels and were quite uniform in size (mostly 3–4 nm). The SBA15-encapsulated uniform Pd nanoparticles were efficient catalysts for solvent-free aerobic oxidation of alcohols. Keywords Palladium nanoparticles SBA-15 Adsorption method Alcohol oxidation
1 Introduction Palladium catalysts are playing essential roles in many important organic transformations such as hydrogenation, Heck and Suzuki couplings and aerobic oxidation of alcohols [1–4]. Recent studies have suggested that Pd nanoparticles may function as active species in these organic reactions. Particularly, recent reports have revealed that supported Pd nanoparticles show promising catalytic performances for the aerobic oxidation of alcohols even under solvent-free
C. Li Q. Zhang (&) Y. Wang H. Wan State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China e-mail: [email protected]
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conditions, which is an important transformation from the viewpoints of establishing a green process for the synthesis of carbonyl compounds to replace the conventional stoichiometric oxidation process using dichromate or permanganate. For example, Pd nanoparticles generated on the hydroxyapatite during the aerobic oxidation of 1-phenylethanol were found to be the true active species, and the hydroxyapatite-supported Pd nanoparticles with a mean size of 3.8 nm were more active that those with a mean size of 7.8 nm for the oxidation of 1-phenylethanol or benzhydrol [4]. Pd nanoparticles supported on magnesia or entrapped in aluminum hydroxide were also efficient catalysts for the aerobic oxidation of alcohols [5, 6]. We reported that the highly dispersed Pd(II) species adsorbed on Al2O3 were transformed into Pd nanoparticles with a mean size of *5 nm during the course of aerobic oxidation of benzyl alcohol, and the generated Pd nanoparticles accounted for the solvent-free aerobic oxidation of benzyl alcohol [7]. Under such background, the controllable synthesis of Pd nanoparticles with tunable and uniform sizes would be helpful for the design of efficient heterogeneous catalysts for these important organic reaction
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