Synthesis Of Nitrogen-doped Carbon-based Nanocomposites And Their Catalytic Performance

Nitrogen（N）doped carbon nanomaterials show excellent catalytic performance due to the change of the structure of carbon materials due to the doping of N,which has become the focus of the current application of catalytic materials.In this work,nitrogen doped carbon sphere（HNCSs）was selected as the carrier,and PtPd/HNCSs and HNCS@CeO₂/CuConanocomposite catalysts were obtained respectively by introducing precious metal alloy（PtPd）and metal oxide-non-precious metal alloy（CeO₂/CuCo）.The morphology,structure and composition of nanocomposites were characterized by TEM,XRD and XPS.Its catalytic activity and stability in the electrocatalytic oxidation of polyols and the hydrogen evolution of aminoborane and its tandem reduction of p-nitrophenol（4-NP）were investigated,which could be used for the development of fuel cells and the treatment of pollutants in the environment.The main contents are:Part I:Application of highly active PtPd/HNCSs nanocatalysts in electrocatalytic oxidation of liquid alcohols.The development and utilization of highly active and persistent electrocatalysts is very important for the commercial application of direct alcohol fuel cells.In this paper,polydopamine-assisted preparation of hollow HNCSs was used as a support for flower-like PtPd nanoparticles.The catalytic performance of PtPd nanoparticles in the electrochemical oxidation of polyols,including methanol,ethanol and ethylene glycol（MOR,EOR and EGOR）was investigated.The effect of Pt/Pd molar ratio on the catalytic activity of these electrooxidation reactions was studied.Electrochemical tests showed that PtPd/HNCSs（only 2 wt.%）showed better catalytic activity and stability than commercial Pt/C（20 wt.%）in the electrochemical oxidation of the three alcohols,which was greatly beneficial to reduce catalyst cost.Through carbon monoxide poisoning experiment,PtPd/HNCSs catalyst was found to have stronger CO toxicity tolerance.Its excellent catalytic performance can be attributed to the large specific surface area and mesoporous structure of HNCSs.In addition,the synergistic effect of PtPd alloy structure is also an important factor.Finally,the catalytic stability experiments were carried out.In MOR,EOR and EGOR,after 200 electrochemical scanning cycles,the peak current corresponding to Pt₃Pd₁/HNCSs could still maintain77.8%,88.9%and 93.9%of the initial cycle,respectively.Kinetic studies have confirmed that the electrochemical processes of MOR,EOR and EGOR are diffusion controlled and irreversible.Part II:High efficiency HNCS@CeO₂/CuCo catalyst for ammonia borane hydrogen evolution and tandem reduction of 4-NP reaction.The application of non-noble metal alloys on suitable porous materials has attracted extensive attention in heterogeneous catalysis,which helps to reduce catalyst cost and improve catalytic activity.In this section,HNCSs@CeO₂ core-shell structure was prepared as a carrier,and HNCS@CeO₂/CuCo nanocomposite was synthesized by introducing CuCo alloy with chemical reduction method,which was used for the water-soluble hydrogen reaction of ammonia borane（NH₃BH₃,AB）and the tandem reduction4-NP reaction.The composition ratio of Cu/Co was optimized,and it was found that HNCS@CeO₂/Cu₁Co₉ showed the best catalytic activity.Its TOF value at 298 K was as high as 15.5 mol_H2·mol^-1_catalyst min^-1,and its apparent activation energy was 21.8 kJ mol^-1,which was lower than the noble metal based catalyst reported in the literature.On the basis of catalytic AB hydrolysis,it was further used in the in-situ reduction reaction of 4-nitrophenol,and its TOF value was 3.7 mol_4-AP mol^-1_catalyst min^-1.This non-noble metal catalyst also has the characteristics of high efficiency and reusable,promoting the development and application of green catalytic reaction.