Dehydrogenation Of Dodecahydro-N-ethylcarbazole Catalyzed By Hydrotalcite-supported Palladium-based Nanocatalys

The storage and transportation of hydrogen are the bottleneck of the development of hydrogen energy industry.Liquid organic hydrogen carriers(LOHC)hydrogen storage utilizes highly reversible reaction of liquid organic molecules with unsaturated double bonds with hydrogen for hydrogen storage and transportation,and achieves hydrogen storage and release through hydrogenation and dehydrogenation reactions.The hydrogen release(dehydrogenation)process needs to meet the hydrogen requirement of mobile devices in different scenarios,and the design and development of high-performance dehydrogenation catalysts,improving the dehydrogenation reaction rate and reducing the dehydrogenation reaction temperature are the focus of LOHC hydrogen storage research.In this paper,supported Pd nanocatalysts were prepared using ultrasonic in situ reduction using MgAl-layered double hydroxides(LDHs)as the support,Fixing the theoretical total metal load of 2.5 wt.%,and Pd-Ni and Pd-Co bimetallic catalysts with different metal ratios were prepared by introducing Ni and Co.The catalytic performance for the prepared catalysts were evaluated by dehydrogenation of 12H-N-ethylcarbazole(H12NEC)as a probe reaction,and characterized by XRD,H2-TPD,H2-TPR,FT-IR,XPS,TEM.The influence of structure,morphology,composition and interaction between metal and support on the dehydrogenation performance of H12-NEC was studied.LDHs were roasted at 300℃ to remove interlayer water to obtain dehydrated LDHs(LDHs-w).LDHs supported ultrafine nano-palladium catalysts(Pd/LDHs-us)with PdCl42-intercalation were prepared using LDHs-w as the support and Na2PdCl4 as the palladium source without using any chemical reductant or stabilizer under sonication.During the ultrasonic in-situ reduction process,the transient high temperature generated by cavitation decomposes the CO32-between the hydrotalcite layers,prompting PdCl42to replace the intercalation layer,while the hydroxyl groups on the surface of LDHs were excited to produce hydrogen radicals with strong reducing properties to reduce PdCl42-to palladium nanoparticles(PdNPs)in-situ.The above method effectively inhibited the agglomeration of PdNPs with an average particle size of 1.8 nm and PdNPs uniformly dispersed on the LDHs.The catalytic activity of Pd/LDHs-us was improved by the formation of complexes between PdNPs and oxygen in the hydroxyl groups on the surface of LDHs,which improved the catalytic stability of Pd/LDHs-us.H12-NEC dehydrogenation rate of 98.8%catalyzed by Pd/LDHs-us was achieved at 180℃,showing excellent catalytic performance.The kinetic study of the dehydrogenation reaction showed that the apparent activation energy of the Pd/LDHs-us was only 90.97 kJ/mol.LDHs supported PdNi bimetallic catalysts(PdnNi1/LDHs)were prepared by wetting impregnation-chemical reduction of Ni2+ to Ni0 using NaBH4,and then reducing Pd2+ to Pd0 by ultrasound-assisted replacement reduction.The hydrogen radicals and Ni0 excited by ultrasound simultaneously rapidly reduced PdCl42-to PdNPs,which promoted the dispersion of PdNi nanoparticles(PdNi NPs)on the surface of LDHs and prevented the agglomeration between nanoparticles.P dNi NPs with an average particle size of 1.72 nm were uniformly distributed on the surface of LDHs,and PdNi alloys were formed.The ultrafine nanoscale and electron effect between Pd and Ni improved the catalytic performance of the H12-NEC dehydrogenation reaction.The experimental results showed that the Pd3Ni1/LDHs catalyst catalyzed the H12-NEC dehydrogenation reaction with a hydrogen release rate of 98.5%at 180℃,which was superior to the monometallic Pd/LDHs catalyst.To further investigate the effect of bimetals on the catalytic performance,LDHs supported PdCo bimetallic catalysts(PdnCo1/LDHs)were prepared by wet impregnationchemical reduction of Co2+ to Co0 using NaBH4 followed by ultrasound-assisted replacement reduction of Pd2+ to Pd0.Ultrasonically excited hydrogen radicals and Co0 simultaneously reduced PdCl42-to PdNPs rapidly,which promoted the dispersion of PdCo NPs on the surface of LDHs and prevented the agglomeration between nanoparticles under ultrasonication.The interaction between Pd and Co metals improved the catalytic performance of the H12-NEC dehydrogenation reaction.At 180℃,the PdsCo1/LDHs catalyzed the H12-NEC dehydrogenation reaction with a hydrogen release rate of 100%within 6 hours,which was better than that of monometallic Pd/LDHs catalyst.It provides a new idea for the preparation of low-cost dehydrogenation catalysts.