Structural and catalytic properties of mono- and bimetallic nickel–copper nanoparticles derived from MgNi(Cu)Al-LDHs under reductive conditions

• Published in: Applied catalysis. A, General Vol. 504; pp. 92 - 102
• Main Authors: Dragoi, Brindusa, Ungureanu, Adrian, Chirieac, Alexandru, Ciotonea, Carmen, Rudolf, Constantin, Royer, Sebastien, Dumitriu, Emil
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.09.2015; Elsevier
• Subjects: Catalysis; Chemical Sciences; Cinnamaldehyde; Copper; Hydrogenation; Layered double hydroxides; Nanoparticles; Nickel; Nanoparticles; Cinnamaldehyde; Nickel; Copper; Hydrogenation; Layered double hydroxides
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2014.11.016

•Highly dispersed (bi)metallic NiCu NPs derived from as-synthesized MgNi(Cu)Al-LDHs.•Extensive characterization of (bi)metallic NPs by in situ XRD, TEM, N2O titration.•(Bi)metallic NiCu NPs outstandingly active in hydrogenation of cinnamaldehyde.•Cu–MgAl-LDH is extremely active even after mild reduction at 150°C. Herein, a way to generate mono- and bi-metallic copper and/or nickel nanoparticles by the direct reduction of Mg(Ni)CuAl-layered double hydroxide (LDH) precursors is reported. Cu and Ni with various molar ratios (0:1, 1:4, 1:1, 4:1 and 1:0) were substituted in the MgAl brucite-like sheets during synthesis. Studies on the evolution of LDH structures under H2 reduction of as-synthesized samples at different temperatures (30–550°C) followed by in situ XRD evidenced the high reducibility of copper cations. The metallic phases generated during reduction of LDHs were dependent on the chemical composition of the sample. The corresponding TEM images display small, very well-dispersed metallic nanoparticles. A positive effect of nickel cations on the dispersion and thermostability of metallic copper phase was also observed, especially with increasing Ni content. For instance, metallic particle sizes of 6.5 and 3.3nm were calculated for the NPs generated by reduction at 500°C of MgCuAl and MgNiCuAl (Ni:Cu=1:1), respectively. Outstanding results for the hydrogenation of cinnamaldehyde in liquid phase were obtained on Cu-rich materials that are able to generate metallic active sites even after reduction at temperature as low as 150°C. Due to the difficulty to detect the metallic phases generated after reduction at 150°C by usual techniques (e.g., TPR, in situ XRD and TEM), Cu0 was put in evidence by the dissociative chemisorption of N2O.