Preparation Of Ni-based Hydrotalcite Nanocatalysts And Their Hydrogenation Performance

In the catalytic hydrogenation reaction,hydrogenation of aromatic compounds for the manufacture of saturated or partially saturated products is of great significance in the fields of chemistry and drug synthesis.Among them,the preparation of nanocatalysts with high activity and stability is the key subject.Thus,a series of nickel-based nanocatalysts with lower price and facile preparation process was prepared from hydrotalcite precursors by adding chelating agents and pore-forming agents,which showed desired catalytic performance in the hydrogenation of several aromatic compounds.Firstly,highly-dispersed nickel-based catalysts?NiMgAlO-in situ?with different Mg/Al molar ratios were prepared from NiMgAl layered double hydroxide precursors?NiMgAl-LDH?by an in situ one-step method in this work.Compared with the catalyst that prepared by the conventional impregnation method(Ni/Mg_0.75Al_0.25O-imp),the as-prepared catalyst with Ni:Mg:Al molar ratio of 1:0.75:0.25 showed excellent catalytic activity and high selectivity?90.6%?for benzylamine in the selective hydrogenation of benzonitrile,mainly attributed to its proper acid-base property.Furthermore,it also showed good stability in benzonitrile hydrogenation with no appreciable loss of its initial activity and selectivity for up to 10 runs,much better than Ni/Mg_0.75Al_0.25O-imp.Notably,no appreciable aggregation of the Ni nanoparticles in NiMg_0.75Al_0.25O-in situ was observed after 10 runs.The strong metal-support interaction in NiMg_0.75Al_0.25O-in situ,as confirmed by X-ray photoelectron spectroscopy and temperature programmed reduction of hydrogen,can suppress the leaching or aggregation of the active Ni nanoparticles during the reaction,accounting for its good stability.Secondly,a novel hierarchical flower-like Ni-Mg-Al-layered double hydroxides was synthesized by a facile hydrothermal method using ethylene glycol as a chelating agent.It exhibited excellent catalytic performance in the hydrogenation of benzoic acid.Transmission electron microscopy,Brunauer-Emmett-Teller,X-ray photoelectron spectroscopy and other characterizations demonstrate that the flower-like hydrotalcite has a hierarchical porous structure compared to the traditional two-dimensional hydrotalcite.Its main active component Ni²⁺was added during the preparation of hydrotalcite precursor,which was favored to obtain smaller and highly dispersed nickel nanoparticles,accounting for the good activity of the catalyst.Furthermore,the strong interaction between the active species and the support can suppress the aggregation of the active Ni nanoparticles during the reaction,resulting in its good stability.Finally,a nickel-based nanocatalyst with high surface area and porous structure was prepared by using carboxymethyl chitosan?CMC?as a template.This nickel-based nanocatalyst showed excellent catalytic performance in the hydrogenation of benzophenone compared to the catalyst prepared without CMC.It was demonstrated that the addition of CMC played a great role in pore formation and increased the catalyst surface area,which facilitates the full exposure of the active nickel,thereby enhancing its catalytic activity.Notably,the modified catalyst also showed good stability in the hydrogenation of benzophenone with no appreciable loss of its initial activity for up to 10 runs,which provided a potential method for the fabrication of such kind of catalysts.