Charge transfer effects on the chemical reactivity of Pd_xCu_1−xnanoalloys

Abstract

aThis work reports on the synthesis and characterization of Pd x Cu 1−x (x = 0.7, 0.5 and 0.3) nanoalloys obtained via an eco-friendly chemical reduction method based on ascorbic acid and trisodium citrate.The average size of the quasi-spherical nanoparticles (NPs) obtained by this method was about 4 nm, as observed by TEM. The colloids containing different NPs were then supported on carbon in order to produce powder samples (Pd x Cu 1−x /C) whose electronic and structural properties were probed by different techniques. XRD analysis indicated the formation of crystalline PdCu alloys with a nanoscaled crystallite size. Core-level XPS results provided a fingerprint of a charge transfer process between Pd and Cu and its dependency on the nanoalloy composition. Additionally, it was verified that alloying was able to change the NP's reactivity towards oxidation and reduction. Indeed, the higher the amount of Pd in the nanoalloy, less oxidized are both the Pd and the Cu atoms in the as-prepared samples. Also, in situ XANES experiments during thermal treatment under a reducing atmosphere showed that the temperature required for a complete reduction of the nanoalloys depends on their composition. These results envisage the control at the atomic level of novel catalytic properties of such nanoalloys.

Catalytic Transfer Hydrogenation of Furfural to 2‐Methylfuran and 2‐Methyltetrahydrofuran over Bimetallic Copper–Palladium Catalysts

“…This new peak was between the (111)r eflections of pure Cu (2 q = 43.38)a nd Pd (2 q = 40.18), whichi ndicates the successful distribution of the Pd atomsi nt he Cu lattice by the formed Cu-Pd alloys and leads to ac hange of the originalC u À Cu lattice spacing and as hift of the diffraction peak. [19] This indicatest hat both Cu 0 and Cu-Pd alloy were presenti nt he 10:1 Cu/Pd ratio catalyst. However,t he diffraction peak of Cu disappearedi nt he 10:3 and 10:5 catalysts( magnified images are presented in the Supporting Information).…”

“…A new weak peak at 42.9° was found. This new peak was between the (1 1 1) reflections of pure Cu (2 θ =43.3°) and Pd (2 θ =40.1°), which indicates the successful distribution of the Pd atoms in the Cu lattice by the formed Cu‐Pd alloys and leads to a change of the original Cu−Cu lattice spacing and a shift of the diffraction peak . This indicates that both Cu 0 and Cu‐Pd alloy were present in the 10:1 Cu/Pd ratio catalyst.…”

“…In the Cu 2p 3/2 spectrum, the main peak at ab inding energy (BE)o f9 30-935 eV was deconvolutedi nto two peaks that correspond to Cu 0 /Cu + + (BE = 931.9 eV) and Cu 2+ + (BE = 933.8 eV) species, respectively. [19,22] The satellite peak aroundB E = 941 eV was clear evidenceo f the existence of Cu 2+ + particlesi nt he Cu-Pd catalysts. As the binding energies of Cu 0 and Cu + + are very close, the Cu LMM spectrumw as recorded to distinguish these two species.…”

“…The Cu 2p 3/2 and Cu 2p 3/2 levels were fitted together with a fixed separation. In the Cu 2p 3/2 spectrum, the main peak at a binding energy (BE) of 930–935 eV was deconvoluted into two peaks that correspond to Cu 0 /Cu + (BE=931.9 eV) and Cu 2+ (BE=933.8 eV) species, respectively . The satellite peak around BE=941 eV was clear evidence of the existence of Cu 2+ particles in the Cu‐Pd catalysts.…”

Catalytic Semi‐Water–Gas Shift Reaction: A Simple Green Path to Formic Acid Fuel

“…The result indicates that iron and ruthenium form an alloy with stoichiometries of 0.6 and 0.4, respectively. Of note, RBS is a more precise analytical tool to determine the stoichiometry of the bimetallic NPs than, for instance, inductively coupled plasma (ICP) analysis . Figure b compares the RBS spectra of both RuFe/SILP‐NTf 2 and RuFe/SILP‐OAc samples.…”