Beneficial Interaction of Gold and Palladium in Bimetallic Catalysts for the Selective Oxidation of Benzyl Alcohol

Abstract

Bi-and monometallic nanoparticles of Au and Pd with a rather narrow size distribution were deposited on polyaniline (PANI) and their structural properties as well as catalytic behavior in the aerobic oxidation of benzyl alcohol were investigated. The size of the mono-and bimetallic particles was controlled in a narrow range (2.4-3.7 nm) using a colloidal preparation route. Admixing Pd to Au resulted in a strong enhancement of selectivity to benzaldehyde reaching a maximum of 98% at full conversion at 100 °C with bimetallic particles containing Au/Pd in a ratio of 1:9. Pure Au particles were significantly more active than pure palladium particles of the same size. Chemical, structural, and electronic properties of the bimetallic catalysts were characterized using high angle annular dark field scanning transmission electron microscopy, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy. The PANI-supported nanoparticles showed a core shell structure with an Au enriched core and a Pd rich shell. The electronic changes occurring upon admixing Pd to Au were examined with X-ray absorption near-edge specroscopy and XPS. The binding energy of core level electrons and the valence d-band occupation in the bimetallic particles were significantly altered in comparison to the monometallic particles, which together with the core shell structure is supposed to be the main reason for the observed changes in the catalytic behavior.

Recent advances in the heterogeneously catalysed aerobic selective oxidation of alcohols

“…77 In this case, the best catalysts comprised clusters ∼1.9 nm diameter containing 80% Au. A similar synergic Au-Pd interaction was reported for bimetallic Au-Pd catalysts supported on polyaniline (PANI) 78 for benzyl alcohol oxidation. Here, the colloidal preparative route provided a narrow particle size distribution (∼3 nm) with a Pd-rich shell encapsulating a Aurich core.…”

Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

“…[13][14][15][16] It is used to add almond flavour in cosmetics, scented products and food. In chemical industries, benzaldehyde is used as a precursor for producing many useful compounds ranging from pharmaceuticals to plastics.…”

Selective Oxidation of 1,6‐Hexanediol to 6‐Hydroxycaproic Acid over Reusable Hydrotalcite‐Supported Au–Pd Bimetallic Catalysts

“…[30] These shifts can be attributed to changes in electronic structure aroundp alladium by alloyingw ith gold. [26] From these observations,w ei nfer that the electronic properties of gold and palladium are significantly changed in the bimetallic catalysts as ac onsequence of Au-Pd interactions (bond formation). These particulari nteractions or Au-Pd nanoalloy centers may be responsible for the high catalytic activity of Au 40 Pd 60 -DDAO/HT in the selective oxidation of HDO to HCA.…”