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

Abstract

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 Pd⁰ 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 (∼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.