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

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 H-2 reduction of as-synthesized samples at different temperatures (30-550 degrees 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 3.3 nm were calculated for the NPs generated by reduction at 500 degrees 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 degrees C. Due to the difficulty to detect the metallic phases generated after reduction at 150 degrees C by usual techniques (e.g., TPR, in situ XRD and TEM), Cu-0 was put in evidence by the dissociative chemisorption of N2O. (C) 2014 Elsevier B.V. All rights reserved.