Structural characterization of bimetallic Pd-Cu vapor derived catalysts

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

“…Like HRTEM, also EXAFS data analysis at the Pd K‐edge showed the presence of small fcc Pd nanoparticles having contracted interatomic distances in the case of the bimetallic sample and that both the monometallic and the bimetallic catalysts have a first shell Pd–O contribution . As recently found using XPS investigations of MVS‐derived samples,, Pd atoms are mainly present in a Pd 0 phase, but small amounts can be in a Pd 2+ one.…”

“…On the other hand, the monometallic Pd/PVPy system synthesized using the same procedure contained metal particles with slightly larger sizes (d m =2.9 nm; SD=1.3 nm) and a broader size distribution (1.0–7.5 nm) (see Figure ), indicating that the presence of Cu affects the metal atoms aggregation. High resolution TEM and lattice fringe analysis of the PVPy‐supported bimetallic catalysts revealed the presence of nanostructured Pd particles having a contracted face cubic centered (fcc) structure . The CuPd/PVPy catalyst showed a high dispersion of the Pd and Cu phases within the PVPy support as evidenced by STEM‐EDS elemental maps of a representative catalyst grain reported in Figure .…”

“…The CuPd/PVPy system showed a high catalytic activity in the Sonogashira reaction of iodobenzene with phenylacetylene carried out with a molar ratio iodide/Pd=1000 at 95 °C in air atmosphere, resulting in 100 % conversion after 2.5 h (specific activity, SA=520 h −1 ) . The catalytic efficiency of CuPd/PVPy was higher than previously reported supported CuPd bimetallic systems, taking also into account the low doses employed.…”

“…Probably due to high Debye–Waller factors and/or interference with other higher coordination shells contributions, even if present, the EXAFS data analysis of bulk CuO does not give this long axial Cu–O distance (see Table ) . The EXAFS data analysis of the CuPd/PVPy sample revealed the presence of two Cu–O coordination shells consistent with Cu 2+ ions coordinated with O atoms at short (1.94 Å) and longer (2.52 Å) distances and a Cu–Pd contribution exhibiting a distance and coordination number compatible with the results obtained at the Pd K‐edge . The two different Cu–O distances found were also confirmed by the presence of the two peaks (labelled C and D) between 8981 eV and 8993 eV in the first derivative of the XANES spectrum of the CuPd sample (Figure ) that are normally associated to a tetragonal distortion of the CuO 6 octahedron that gives shorter equatorial and longer axial Cu−O bonds.…”

“…The catalytic efficiency of CuPd/PVPy was higher than previously reported supported CuPd bimetallic systems, taking also into account the low doses employed. Moreover, thanks to the coordinative capability the PVPy support, the amounts of metals leached by the CuPd/PVPy system were very low (0.6 ppm of Pd and 3.0 ppm of Cu in the crude reaction product) with respect to the ones of an analogous system supported on carbon …”