Hydroxyapatite-Supported Palladium Nanoclusters:  A Highly Active Heterogeneous Catalyst for Selective Oxidation of Alcohols by Use of Molecular Oxygen

Abstract

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.

Catalytic oxidation of benzyl alcohol on Au or Au–Pd nanoparticles confined in mesoporous silica

“…The present stringent ecological standards have forced researchers to develop new environmentally benign methods. Accordingly, a remarkable number of metal-catalyzed aerobic processes, especially based on Pd [7][8][9], Ru [10][11][12], and Cu [13,14] complexes, have been developed. In recent years, the unexpectedly high activity of Au as a lowtemperature CO oxidation catalyst [15] has initiated intensive research in the use of Au nanoparticles for the liquid-phase oxidation of alcohols [16][17][18][19][20].Gold and palladium Mesoporous SBA-15 Nanoparticles Oxidation Benzyl alcohol…”

Characteristics of Au/HMS catalysts for selective oxidation of benzyl alcohol to benzaldehyde

“…These materials are not only expensive but also have serious toxicities. Several homogenous Pd [4][5][6], Cu [7,8] or Ru [9][10][11] catalysts are able to serve for the selective oxidation of alcohols, but they require the use of organic solvents or high-pressure oxygen. The present stringent ecological standards have forced researchers to develop new environmental friendly methods.…”

Green Oxidation of Alcohols to Carbonyl Compounds by Heterogeneous Photocatalysis

“…A wide range of supported platinum and palladium catalysts has long been reported to exhibit high catalytic performance in the oxidation of alcohols. [15][16][17] Au/Pd-TiO 2 catalysts showing high turnover frequencies (up to 270 000 turnovers per hour) have been also proposed. [18] These catalysts, used for carrying out the oxidation of benzyl alcohol to benzaldehyde, showed an alcohol conversion of 74.5 % and an aldehyde selectivity of 91.6 %, benzyl benzoate being the only detected byproduct.…”