XAFS structural characterization of Cu vapour derived catalysts supported on poly‐4‐vinylpyridine and carbon

Abstract

The use of supported metallic nanoparticles (NPs) is fundamental for the development of new catalysts with high activity and selectivity. For this reason, the choice of a suitable support, the selection of metal precursors and the preparation methods become quite important. In the present work, we show the structural effects induced on metal vapour synthesis (MVS) derived Cu NPs by different carbon-based supports such as poly-4-vinylpyridine (PVPy) and carbon and how these effects can affect their catalytic activities in Huisgen azide-alkyne cycloaddition reactions (CuAAC). The influence of the two supports on the structure of the Cu NPs was studied using high-resolution transmission electron microscopy (HRTEM) and X-ray absorption fine structure (XAFS) spectroscopy. As shown by XAFS analysis, Cu NPs, immobilized on PVPy, resulted in a Cu(I) oxidized phase while the ones on carbon were in a Cu(II) phase. The structural effects induced by the different supports determined a completely different catalytic behaviour of the two catalytic systems in a model CuAAC reaction: the PVPy-supported Cu system was active and re-usable whereas the analogous carbon-based system was almost inactive.

Characterization of a Poly‐4‐Vinylpyridine‐Supported CuPd Bimetallic Catalyst for Sonogashira Coupling Reactions

“…Concerning the XAFS data analysis, at the Cu K-edge ( Figure 4), in the monometallic Cu/PVPy sample, no metallic phase was found. [41] The depositiono fm onometallic Cu on PVPy resulted in the formation of Cu 2 On anoparticles, [41] as already observed by other authors, [42] with at hin CuO surface layer.T he presence of Cu 2 On anoparticles, in the Cu/PVPy monometallic sample, is clearlyv isible from the position of the peak in the near edge region shown in Figure 4( dotted line). This single absorption peak is normally assigned to the electric dipole-allowed transitions, characteristic of Cu 1 + (3d 10 )s amples like Cu 2 O.…”

Total Synthesis of Asparenydiol by Two Sonogashira Cross-Coupling Reactions Promoted by Supported Pd and Cu Catalysts

“…As detected by X-ray absorption fine structure spectroscopy and high-resolution transmission electron microscopy, this catalyst contains Cu(I) nanoparticles (mean diameter of 3.3 nm) in form of copper oxide (Cu 2 O). 27 Reaction rate and isolated yield (53%) significantly increased in this case (Table 2, entries 1 and 2), although it was still not satisfactory.…”

“…For the first Sonogashira cross-coupling, we tested a range of commercially available supported palladium catalysts [Pd EnCat™40, FibreCat 1007, Pd(PPh 3 ) 4 PS, and PdCl 2 (PPh 3 ) 2 /PS] and two polyvinylpyridine(PVPy)-supported catalysts recently developed by our research group (Cu/PVPy and Pd-Cu/PVPy). 26,27 The ability of the PVPy resin to promote M-H-type alkenylations, ensuring also very low metal leaching, was previously reported. 28,29 The reaction conditions were initially optimized using Pd EnCat TM 40 as a catalyst (Table 1), because this was already successfully tested for the synthesis of some natural compounds.…”

Hybrid Au/CuO Nanoparticles: Effect of Structural Features for Selective Benzyl Alcohol Oxidation

“…However in Cu(I) compounds, there are no holes in the 3d orbitals, in Cu(II) ones, the presence of a d 9 configuration gives the weak pre-edge absorption peak A, corresponding to a 1s → 3d dipole forbidden but quadrupole-allowed transition. 37 This weak peak represents the signature of the presence of divalent copper. Cu(II) compounds have also another important characteristic given by the higher energy values of their X-ray absorption edges compared to Cu(I) compounds.…”