Preparation Of Activated Carbon Supported Palladium-based Nanocatalysts And Study Of Catalytic Dehydrogenation Reactio

In this paper,loaded palladium-based nano catalysts（Pd/AC）were prepared using activated carbon（AC）as a carrier without any protective and stabilizing agents via different reduction methods.The structure,composition and morphology of the prepared catalysts were characterized by N₂ adsorption-desorption,XRD,XPS,TEM,TG and Raman,and their catalytic performance was investigated using the dehydrogenation reaction of fully hydrogenated N-ethylcarbazole（12H-NEC）as a probe reaction.The Pd/AC catalysts were prepared by ultrasonic impregnation-carbothermal reduction using AC as the carrier and reducing agent,and Pd（NO₃）₂ as the precursor.The obtained Pdnanoparticles（PdNPs）with particle size distribution of 4.05-8.50 nm and an average particle size of 6.63 nm were uniformly dispersed on the surface of AC under the reduction condition of 2 h at 500°C.There was no apparent agglomeration of PdNPs.The exposed main crystalline surface was the Pd（111）crystalline surface.The results of the catalytic 12H-NEC dehydrogenation reaction showed that the hydrogen release efficiency was 95.68%for 6 h at 180°C.The carbothermal reduction method promotes the graphitization of activated carbon while reducing Pd²⁺to PdNPs,which improves the catalytic performance of the catalysts.The Pd/AC-EG,Pd/AC-EGus catalysts were prepared by thermal reduction and ultrasound-assisted reduction methods using AC as the carrier,ethylene glycol as the reducing agent,and Pd（NO₃）₂ as the precursor,respectively.The PdNPs in the Pd/AC-EG catalysts prepared by reduction at 160°C for 6 h were uniformly dispersed on the surface of AC with the particle size distribution between 3.25-9.67 nm and the average particle size of 6.03 nm.The results of 12H-NEC dehydrogenation catalyzed by Pd/AC-EG and Pd/AC-EGus showed that the hydrogen release efficiency at 180℃for 6 h reach91.36%and 93.7%,respectively.After 4 cycles of Pd/AC-EGus catalyst,the hydrogen release efficiency was 91.54%,respectively.The PdNi/AC catalysts were prepared by ultrasound-assisted chemical reduction using AC as the carrier,NaBH₄ as the reducing agent,and Na₂PdCl₄ and Ni Cl₂ as the precursors.The Pd-Ni NPs prepared under the conditions of Pd/Ni molar ratio of 7:3,NaBH₄/Ni²⁺molar ratio of 2:1,Ni²⁺reduction time of 2 h and ultrasonic reduction of Pd²⁺power of 300 W for 3 h were uniformly dispersed on the surface of AC and formed an alloy structure with the particle size distribution ranging from 5.21 to 19.39 nm and the average particle size of 9.98 nm.The results of the catalytic 12H-NEC dehydrogenation reaction showed that the hydrogen release efficiency was 94.65%for 6 h at 180°C.It was shown from the experimental results that the loaded palladium-based catalysts with uniformly dispersed metal nanoparticles and good catalytic performance can be prepared by using AC as the carrier without adding any protector and stabilizer via the different reduction methods.Among them,the loaded nano palladium-based catalysts prepared by carbothermal reduction exhibited the best catalytic performance.The preparation conditions of the catalyst were simplified by ultrasonic-assisted chemical reduction,and the catalyst was of stability.