Direct synthesis of hybrid layered double hydroxide-carbon composites supported Pd nanocatalysts efficient in selective hydrogenation of citral

This present study reports a facile one-pot strategy for the direct synthesis of hybrid layered double hydroxide (LDH)-carbon composites supported palladium nanocatalysts by the in situ reduction of PdCl42--intercalated MgAl-LDH combined with amorphous carbon under mild hydrothermal conditions. The results demonstrated that most of the Pd(II) species intercalated in the interlameller space of MgAl-LDH could be reduced in situ to metallic Pd-0 species, and simultaneously, the hybrid structure of the LDH-C composites facilitated the formation of uniform Pd nanoparticles with small diameter, as well as the strong metal-support interactions. Furthermore, with the decreasing proportion of the LDH component in LDH-C composites, the average diameter of Pd nanoparticles decreased progressively and the metal-support interactions were weakened. The as-formed supported Pd nanocatalyst with Pd loading of 5.5 wt% was found to show a superior catalytic activity in the liquid-phase selective hydrogenation of citral than other supported Pd nanocatalysts, while the one with the Pd loading of 2.7 wt% yielded a much higher yield of citronellal (similar to 80.0%) at 100% conversion. The catalytic performance of Pd nanocatalysts was proposed to be mainly related to both the metal-support interactions and the compositions of hybrid LDH-C composite supports.