Controlled Synthesis And Catalytic Properties Of Nickel And Palladium-based Composites

In recent years,with the rapid development of nanotechnology and the great emphasis on the sustainable development of environment and energy,cost-effective and stable catalytic materials have been widely used in organic and electrocatalytic reactions.The catalysts with special structures can not only lead to the enhancement of the activity,selectivity and stability,but also reduce the dosage of noble metals as well as the cost of catalysis.Moreover,following the idea of green chemistry,environmental pollution can also be controlled if the reactions are carried out under green conditions with less or even no emissions.In this dissertation,nanocatalysts with specific structures were fabricated by wet chemistry methods,which shows excellent catalytic performances in hydrogenation reaction of nitrocompounds,Suzuki-Miyaura reaction,oxidative esterification of alcohols as well as electrocatalytic hydrogen evolution reaction(HER).Moreover,the catalytic mechanisms,the interactions between individual components and the relationship between the structures and performances of the catalysts were also studied.(1)Hydrogenation of nitrophenls catalyzed by carbon black-supported nickel nanoparticles under mild conditions.A magnetically separable carbon black(CB)supported nano-Ni catalyst was prepared by a facial wet chemistry method.Compared with pristine Ni catalyst,the Ni particles supported on the surface of CB has smaller particle size and narrower size distribution.The Ni/CB catalyst exhibits high catalytic activity for hydrogenation of nitrophenols under mild conditions.The high performance obtained here can be attributed to the specific characteristics of the nanostructure of the catalyst and the synergistic effect between nano-Ni and CB,including plenty of oxygen-containing groups of CB for anchoring Ni atoms,strong adsorption ability for organic molecules and good conductivity for electron transfer from CB to Ni nanoparticles.(2)Synthesis of carbon-based binary metallic composites as highly active catalysts for heterogeneous green Suzuki-Miyaura coupling reaction.A magnetically separable core-shell-like Ni-Pd/CB catalyst was synthesized via a facile sequential reduction strategy:preparation of Ni/CB first followed by Pd deposition onto Ni core through chemical substitution method.While the PdCu alloy nanoparticles supported on nitrogen doped carbon black(NCB)was prepared via a facile one-pot coreduction process.Both of the catalysts exhibite excellent catalytic performance,general applicability and good cycling stability in Suzuki-Miyaura coupling reactions in air under mild conditions without using toxic solvents,ligands or protective atmosphere,achieving green and efficient catalysis.As for the PdCu/NCB catalyst,nitrogen doping effectively contribute to the formation of individually isolated PdCu hybrid nanoparticles with a uniform dispersion,smaller size and narrower size distribution,leading to excellent catalytic performance.The core-shell-like structure and alloy structure increases the utilization of Pd and meanwhile reduces the catalysis cost.The excellent performance of these two catalysts is mainly due to the synergistic effect between individual components,especially the synergy between the two different metals.(3)Direct oxidative esterification reaction of alcohols catalyzed by nitrogen-doped carbon black supported PdBi alloy nanocatalyst under mild conditions.NCB supported binary PdBi alloy catalyst was synthesized by a one-pot coreduction process in the liquid phase,where the Pd/Bi mole ratios can be easily tuned by varying the batch charge of the raw materials.The Pd/Bi catalyst with a Pd/Bi mole ratio of 1/1 exhibits the most excellent catalytic activity as well as good cycling stability for the direct oxidative esterification of benzyl alcohol with aliphatic alcohol.Compared with homogeneous catalytic systems,heterogeneous oxidative esterification reaction catalyzed by PdBi/NCB alloy nanocatalyst can be carried out under milder conditions with shorter reaction time and easier product postprocessing.(4)Synthesis of ternary NiCo2S4 supported on nitrogen-doped carbon black as a highly efficient catalyst for hydrogenation reaction of nitrophenols.An NCB supported NiCo2S4 catalyst was successfully prepared by a facile one-pot solvothermal approach.NiCo2S4 can be used not only as supercapacitor materials,but also competitive as catalytic materials in hydrogenation reactions.The NiCo2S4/NCB catalyst exhibits excellent catalytic activity and durability for heterogeneous catalytic hydrogenation of nitrophenols under mild conditions.With the influence of both the inductive and conjugation effects,the reactivity of the nitrophenols follows the order of m-nitrophenol>o-nitrophenol>p-nitrophenol,where each reaction can be described by the pseudo first order kinetics.(5)Straightforward synthesis of self-supported ternary Ni-P-Pt/Ni foam(NF)electrodes in the liquid phase with trace Pt deposition for efficient alkaline hydrogen evolution reactionWe developed a facile,mild and safe way to synthesize trace Pt deposited ternary Ni-P-Pt/NF electrocatalysts in the liquid phase for HER.The synthetic approach is composed of a sequential straightforward solvothermal preparation of self-supported Ni-P/NF electrode and subsequent chemical replacement of Pt species without any hazardous and hypertoxic emissions.The trace Pt deposited electrocatalyst shows excellent performance to HER in both acidic and alkaline media.In particular,it requires a desirable durability without noticeable decay after 24 h in 1 M KOH aqueous solution,achieving a coordination between the catalysis cost and hydrogen production.The catalytic performance is superior to that of Pt/NF and Ni-P/NF catalysts.Confirmed by X-ray photoelectron spectroscopy and DFT theoretical calculations,the synergistic effect between Pt and Ni-P individuals makes tremendous contributions to the enhanced HER activity.