| Catalysts play a vital role in the chemical industry, because they are applied in more than 80% of chemical process. Developing highly efficient catalysts is considered to be an effective way to realize the goal of green production. In the past few years, supported catalysts, especially for carbon supported catalysts, were widely used to synthesize fine chemical products. Obiviously, it is significantly important for chemical plants to enhance the activity and selectivity of their catalysts to improve the production benefits. Thus, it is of great value in both theory and practice to design and develop efficient, selective and low-cost carbon supported catalysts.Focusing on carbon supported catalysts, we developed a one-step pyrolysis method to prepare nitrogen-doped carbon supported iron-based and cobalt-based catalysts, which exhibited excellent activity and selective towards hydrogen evolution reaction (HER) and catalytic hydrogenation, respectively. Glucosamine hydrochloride, a biomass-derived compound, was chosen as both carbon and nitrogen sources, while melamine was used as soft template. The catalysts were synthesized through thermal polymerization of the mixture of glucosamine hydrochloride, melamine and metal salts. TEM characterizations revealed that the nanoparticles were uniformly dispersed on the carbon matrix and the elemental metal were covered by carbon layers. The good dispersion and special encapsulation structure gave a big boost to the catalytic performance.For the Fe2O3/Fe@CN catalyst, we investigated the structure-activity relationship by studying its HER performance. During the calcination process, reducing gases such as H2 were generated to reduce partial metal oxide to metallic Fe (Fe0), which was further coated by carbon, forming the special encapsulation structure. The defects outside the coated Fe0, observed by TEM characterization, were proved to be beneficial for the catalytic activity. In addition, the synergistic effect of Fe2O3 and Fe0 on the carbon surface accelerate the HER process via the pathway of Volmer-Heyrovsky. The Fe2O3 site preferentially adsorbed OH" generated by water decomposition, while a nearby Fe0 site would facilitate H adsorption. The electrochemical tests revealed that the Fe2O3/Fe@CN catalyst exhibited an overpotential of 0.33 V at a current density of 10 mA/cm2 and maintained its electrocatalytic activity for 30000 seconds without any degradation in the stability test.For the CoOx@CN catalyst, we investigated the structure-activity relationship by studying its performance towards hydrogenation of 2,3,5-trimethylbenzoquinone (TMBQ) to 2,3,5-trimethylhydroquinone (TMHQ). Similarly, the encapsulation structure was also observed in CoOx@CN catalyst. The Co-based nanoparticles were dispersed more evenly on the carbon support and the average size was about 9 nm. The CoOx@CN catalyst showed remarkable activity (92%) and selectivity (> 99%) towards TMBQ hydrogenation under the reaction temperature of 100? and hydrogen pressure of 2 Mpa. The condition experiment disclosed that the metallic Co was responsible for the hydrogenation of TMBQ. Further, the DFT calculation was carried out to systematically study the reaction mechanism, indicating that the excellent selectivity towards TMHQ was due to the lower energy barrier of desorption (0.33 eV) than that of sequential hydrogenation (0.57 eV).Above all, we developed a one-step pyrolysis method to synthesize iron-based and cobalt-based composite catalysts, which displayed excellent performance in HER and TMBQ hydrogenation, respectively. The activity and stability of the catalysts were greatly improved by the merits of small particle size, uniform distribution and special encapsulation structure. We expect that our research would contribute to the further design and synthesis of non-noble metal catalysts. |
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