Preparation Of Pd-based Catalysts And Its Performance For The Hydrogen Evolution From Formic Acid

Formic acid（FA）is considered as an ideal liquid hydrogen storage material due to its high hydrogen content（4.4 wt%）,stable chemical properties and easy realization of reversible hydrogen storage.Constructing highly active catalyst for formic acid dehydrogenation is the crux to achieve the large-scale application of formic acid as hydrogen storage material.At present,supported Pd-based catalysts have been extensively investigated in hydrogen evolution of FA.The results show that the performance of these catalysts is closely related to the active components and the properties of the supports.How to regulate the structure of active components and supports to achieve high efficiency hydrogen production from formic acid is one of the research hotspots.Herein,a series of new Pd-based catalysts were designed and prepared for dehydrogenation of formic acid,revealing the influence of catalyst composition and structure on catalyst performance.The specific research contents are as follows:（1）N-deficient ordered mesoporous graphitic carbon nitride（N-ompg-C₃N₄）was synthesized via a hard template method,and it was proposed to optimize the metal-support interaction by selecting etching agent to remove the template and design the support defects.Then Ag Pd/N-ompg-C₃N₄was prepared by an impregnation reduction method for hydrogen production from FA.Among many catalysts synthesized,Ag_0.1Pd_0.9/N-ompg-C₃N₄catalyst has excellent catalytic performance,high activity,high selectivity and excellent cycling stability.In addition,the absence of support surface is the most favorable for formic acid dehydrogenation when the etching agent is Na OH.The experimental and characterization results showed that the unique structure of N-ompg-C₃N₄resulted in higher specific surface area and surface defects.The synergistic effect between Ag Pd alloy and N-ompg-C₃N₄and the charge transfer from Pd to Ag are the main reasons for the improvement of its catalytic performance.（2）In this work,two-dimensional graphitic carbboonn nitride nanosheets（2D CNNs）were prepared by a molten salt soft template method,and are used as a scaffold to load Ag Pd alloy.TThhee performance of Ag Pd/2D CNNs foorr hydrogen production under visible light（λ>400 nm）is investigated.Benefiting from plasmonic and a Mott-Schottky,alloying effects,along with the unique 2D nanosheets structure with a high specific surface area,the resultant Ag_0.1Pd_0.9/2D CNNs affords superior performance under visible light,including 100%H₂selectivity,100%conversion,cycle performance,hydrogen evolution rate of 231.6 mmol·h^-1and the corresponding TOF value of 2936.8 h^-1,which is 1.87 times and 3.5-fold higher than that of Ag_0.1Pd_0.9/2D CNNs under no light(1573.5 h^-1)and that of Ag_0.1Pd_0.9/CN(837.2 h^-1)under visible light,respectively,even better than most of the noble metal heterogeneous catalysts.