Preparation Of Pd-based Formic Acid Dehydrogenation Catalytic Materials By Atmospheric Pressure Cold Plasma

Formic acid?HCOOH?is a cheap,non-toxic,ease of storage and transportation,and abundant renewable source for generating hydrogen.The development and utilization of direct formic acid fuel cells?DFAFCs?using HCOOH as a hydrogen storage medium is an effective method to solve the problem of energy depletion and environmental deterioration.In this work,a simple atmospheric pressure?AP?dielectric barrier discharge cold plasma has been employed to synthesize various Pd-based catalytic materials for HCOOH dehydrogenation application by using H₂PdCl₄ as Pd precursor and activated carbon as the support.The main research results are as follows:The effects of AP cold plasma discharge atmosphere?H₂,O₂,Ar,Air?,as well as cold plasma and thermal treatment sequence on the structure and performance of the Pd/C catalytic materials have been investigated.The Pd/C-CP?Pd/C-H₂P?prepared by thermal reduction treatment followed by AP cold plasma treatment with H₂ as the plasma discharge working gas exhibits the best catalytic activity for HCOOH dehydrogenation.The strong single-channel discharges in H₂ plasma generates a strong electric field,which promotes the migration of active species to the outer surface of the support.The Pd/C-CP possesses not only small size?2.6 nm?and high dispersion of Pd nanoparticles,but also high concentration of metallic Pd and Pd/C atomic ratio?0.229?on the surface of the Pd/C-CP catalytic material resulting from the migration of the electroneutral Pd species under the Coulomb repulsion effect of the electrons in the plasma and the active hydrogen species.In contrast,the process of negatively charged oxygen discharge in O₂ and Air plasma caused severe ablation of the carbon support,while the discharge of Ar plasma was mild and the regulation effect was poor.As the plasma treatment destroys the oxygen-containing functional groups on the surface of the support,plasma treatment followed by thermal reduction treatment leads to larger size of Pd nanoparticles in Pd/C-PC,thus the activity is deteriorated.The Pd/C-CPsynthesized by thermal reduction followed by AP H₂ cold plasma treatment shows higher catalytic activity and stability than the commercial Pd/C catalyst.The high catalytic activity of Pd/C-CP is mainly attributed to the small size of Pd nanoparticles.The high catalytic stability of Pd/C-CP is ascribed to the strong metal-support interaction induced by cold plasma and HNO₃pre-oxidation treatment,which leads to less decrease in Pd/C atomic ratio,Pd leaching,and the stable size of Pd nanoparticles.The effect of the second metal?Au,Pt,Ru,Ag,Cu,Ni?addition on the structure and performance of Pd-based bimetallic catalytic materials was also investigated.With the addition of Au and Pd/Au molar ratio was 4/1,the Pd₄Au₁/C-CP showed the highest catalytic activity and stability.The HCOOH decomposition rate reached 95.9%within 4 hours,and the initial turnover frequency was about 808.6 h^-1.The apparent activation energy of the HCOOH dehydrogenation reaction was 27.25 kJ·mol^-1,and the total amount of gas generated after three cycles of testing was 1.33,5.87,and 8.56 times as that of the commercial Pd/C,respectively.The plasma effectively promoted the redispersion of Pd-Au particles in Pd₄Au₁/C-CP and had a higher degree of alloying.At the same time,a strong electric field regulated the enrichment of more active components in Pd₄Au₁/C-CP on the outer surface of the support.In summary,thermal reduction followed by AP H₂ cold plasma is an effective method for preparing high performance Pd-based formic acid dehydrogenation catalytic materials.On the one hand,the strong electric field and Coulomb repulsion in the plasma effectively regulate the distribution of the active species on the outer surface of the carbon support and strengthen the metal-support interaction.On the other hand,cold plasma promotes the redispersion of Pd-Au agglomerated particles and increases the alloying degree.This work has theoretical significance and practical application value for the development of high-performance Pd-based HCOOH dehydrogenation catalytic materials.