Synthesis Of Supported Pd-Co-Ni Catalysts And Their Catalytic Performance For Dehydrogenation Of Formic Acid

Hydrogen,as a clean and efficient energy source,can effectively solve the pollution trouble of fossil fuel.Formic acid?HCOOH,FA?is a liquid chemical hydrogen storage material.It is safe,stable,non-toxic,simple to synthesize,with a high gravimetric hydrogen capacity?4.4 wt%?.With the help of catalysts,FA is able to dehydrogenate selectively into CO₂ and H₂.More importantly,FA can be regenerated after dehydrogenation by carbon dioxide hydrogenation reaction.Therefore,finding cost-effective catalysts is an essential issue for the commercial application of FA.Based on literature research,this paper designed and prepared3-aminopropyltriethoxysilane(C₉H₂₃NO₃Si,APTS)modified PdCoNi catalyst nanoparticles supported by different substrates,and studied their catalystic performance and mechanism for dehydrogenation of FA in sodium formate?HCOONa,SF?/FA system.First,an APTS modified three-dimensional lamella TiO₂?B?is prepared as a substrate to support PdCoNi nanoparticles?NPs?,which is further used to enhance the catalytic activity of the active component PdCoNi NPs effectively.The results indicate that the addition of APTS can modify the amino group?-NH₂?on the surface of TiO₂,and Pd_0.6Co_0.2Ni_0.2/NH₂-Si-TiO₂ is prepared by changing the ratio of APTS and TiO₂,which demonstrates excellent catalytic performance.The initial conversion frequency TOF_inital of the catalyst is 397 mol_H2?mol^-1_metal?h^-1(h^-1)at room temperature,and the apparent activation energy E?is 49.92 kJ?mol^-1.The analysis shows that TiO₂?B?modified by APTS can inhibit the agglomeration of PdCoNi NPs,reduce the size of NPs,without affecting the electron transfer of Co and Ni to Pd.Furthermore,-NH₂increases the opportunity of sufficient contact for the HCOO^-with catalysts,which also greatly improves the catalytic activity.Subsequently,APTS-modified nitrogen-containing hollow carbon spheres(C_Ball)is also used as substrate for FA dehydrogenation catalysts,and the catalyst PdCoNi/N-Si-C_Ball is successfully prepared.Control experiments prove that without C_Ball,APTS can still significantly enhance the catalytic activity of PdCoNi NPs,and the catalytic activity of PdCoNi NPs loaded on C_Ball modified by APTS can be further improved.By optimizing the amount of APTS and the ratio among metals,Pd_0.8Co_0.1Ni_0.1/N-Si-C_Ball is prepared with 100%hydrogen selectivity and good cycle performance,the value of TOF_inital can reach 745 h^-1 at room temperature,E?is 39.50kJ?mol^-1.It is found that APTS is doped with pyrrole N on C_Ball without affecting carrier structure,which could avoid the formation of extremely large particles.When the content of Pd comes to 80 at%,the catalyst shows the best performance,and Pd can effectively protect part of Co and Ni from corrosion which improves the stability of the catalyst.Finally,APTS-modified nitrogen-containing nanosheets?CN?is prepared and used to support PdCoNi NPs.The combination of APTS and CN only forms the doping of pyrrole N?N-CN?without change the original ratio of pyridine N and graphite N in CN.N-CN as a substrate can induce the formation of ultrafine,monodisperse,two-dimensional PdCoNi NPs,increasing the proportion of catalytically active sites and effective active components.Compared with CN,N-CN has a certain degree of hydrophobic performance and does not affect the electron transfer between Pd,Co and Ni.Pd_0.6Co_0.2Ni_0.2/N-CN with optimal ratio exhibits high catalytic activity with a TOF_initial of 1249.0 h^-1 at room temperature,which is more than 6 times that of Pd_0.6Co_0.2Ni_0.2/CN.And E?is determined to be 20.04 kJ?mol^-1.The reusable catalyst still can release 232 mL ofgas in 10 rnin and achieves 94%conversion in the 4th catalytic reuse.The analysis shows that N-CN can effectively protect part of Co and Ni from corrosion during the cycle,which enhance the cycle stability of Pd_0.6Co_0.2Ni_0.2/N-CN.