Preparation Of Nitrogen-doped Carbon-supported Nano-palladium Catalyst And Study On Catalytic Dehydrogenation Reaction

The supported palladium catalysts(Pd/NC)are prepared by the chemical reduction method without any protective agent using nitrogen-doped porous carbon(NC)derived from ZIF-8 as the support.The structure,composition and morphology of the prepared catalysts are characterized with UV-Vis,XRD,XPS and TEM.Their catalytic performances are investigated by the catalytic dodecahydro-N-ethylcarbazole(12H-NEC)dehydrogenation reactions.The Pd/NC catalysts are synthesized with the ascorbic acid(AA)as the reductant,the NC as the carrier and the Na₂Pd Cl₄ as the palladium source.The prepared Pd nanoparticles(Pd NPs)uniformly disperse on the surface of NC under the reduction conditions of AA/Pd molar ratio of 1.2:1 and 60?for 2 h.The particle size distribution of Pd NPs ranges from 2.02 nm to 4.32 nm with an average size of 3.17 nm.The crystal structure of Pd NPs belongs to the face-centered cubic structure and the exposed crystal faces are mainly Pd(111)crystal plane.The results of catalytic 12H-NEC dehydrogenation reaction show that the hydrogen release amount is 5.67 wt%for 10hours at 180?and remains 5.09 wt%after four cycles.The N doping decreases the electronic binding energy of Pd and improves the catalytic activity.The coordination of Pd with N enhances the catalytic stability of Pd/NC.The Pd/NC catalysts are synthesized by ethanol reduction with the NC as the carrier and the Na₂Pd Cl₄ as the palladium source.The prepared Pd nanoparticles uniformly disperse on the surface of the NC under the reduction conditions of Et OH/H₂O molar ratio of 3:1,Na OH concentration of 0.03 mol/L and oil bath temperature of 110°C for 12h.The particle size distribution of Pd NPs ranges from 1.96nm to 4.03 nm with an average size of 2.81 nm.The crystal structure of Pd NPs belongs to the face-centered cubic structure and the exposed crystal faces are mainly Pd(111)crystal plane.The results of catalytic dodecahydro-N-ethylcarbazole dehydrogenation reaction show that the hydrogen release amount is 5.73 wt%for 10 hours at 180?and remains 5.26 wt%after four cycles.The-OH on ethanol is oxidized by Pd²⁺to aldehydes.The aldehydes are not stable and easily to be oxidized to acetic acid.They will be converted into CO₂ or carbonate in alkaline medium,and the electrons obtained in the oxidation reaction will reduce Pd²⁺.The Pd-Ag/NC catalysts are synthesized by ethanol reduction with the NC as the carrier,the Na₂Pd Cl₄ and Ag NO₃as the source of palladium and silver.The prepared Pd-Ag nanoparticles disperse on the surface of the NC and form alloy structure under the reduction conditions of Et OH/H₂O molar ratio of 3:1,Na OH concentration of 0.03mol/L and oil bath temperature of 110°C for 12 h.The particle size distribution of Pd-Ag NPs ranges from 2.24 nm to 4.85 nm with an average size of 3.65 nm.The results of catalytic dodecahydro-N-ethylcarbazole dehydrogenation reaction show that the hydrogen release amount is 5.40 wt%for 10 hours at 180?and remains 5.08 wt%after four cycles.The electronic interactions between Pd-Ag alloy nanoparticles enhance the stability of the catalyst.It is indicated from experimental results that the ultrafine Pd NPs with better dispersion can be prepared by ethanol reduction without any protective agent using the NC as the carrier.The prepared Pd/NC catalyst exhibits excellent catalytic dehydrogenation and recycling performance.