Study On The Performance Of Pd Catalyst In Formic Acid Dehydrogenation Regulated By Support Structur

Hydrogen（H₂）is considered to have broad development prospects due to its high energy density,extensive sources,and renewable characteristics.However,the storage,transportation,and safety issues brought by H₂ greatly restrict the development of the“hydrogen economy”.Formic acid（FA,HCOOH）is considered a potential H₂ storage material because of its high hydrogen content(mass density of 4.4 wt%,volume capacity of 53.4 g·L^-1),superior stability,low toxicity and portability.In the FA dehydrogenation reaction,the size of the active center and the electronic properties of the catalyst have important effects on the activity and selectivity of the catalytic reaction.For heterogeneous catalysts,the carrier plays a crucial role.Therefore,a series of Pd nanocatalysts have been synthesized through the design of carrier structures and the modulation of active components to achieve highly active and selective decomposition of FA to produce H₂ at room temperature.The main research contents are as follows:（1）The Pd nano-catalyst（Pd/C-SiO₂）for the decomposition of FA was prepared by in-situ composite of porous carbon and SiO₂ as carrier in a one-pot method.Combined with the characterization results and performance tests,the composite carrier C-SiO₂ can reduce the size of Pd nanoparticles（NPs）,optimize the electronic state of Pd,and enhance the hydrophilicity of the catalyst.Compared with Pd/C and Pd/SiO₂,the synthesized Pd/C-SiO₂ exhibits the best catalytic performance for the dehydrogenation of FA with TOF value of 2297 h^-1,and H₂ selectivity of 100%at 30°C.（2）A series of N-doped carbon carrier supported Pd NPs were prepared by co-carbonization of N-containing zeolite imidazole skeleton（ZIF-8）and secondary N/C source（melamine,xylitol,urea and glucose）modifiers for the decomposition of FA to generate H₂.Characterization analysis suggests that the introduction of secondary N/C sources can alter the morphology,specific surface area,N content and type of porous carbon,thereby further affecting the catalytic performance of Pd NPs.When melamine was used as the modifier,the resulting catalyst(Pd/CN_ZM)has high N content（8.36wt%）and uniform mesoporous pores,which make Pd NPs evenly dispersed on CN_ZMwith the size of 3.3 nm.Thus,Pd/CN_ZM exhibits superior catalytic activity and 100%H₂ selectivity,and its TOF value is 4157 h^-1 at 50°C.Moreover,the influence of N atom on FA dehydrogenation and the favorable reaction path were revealed by theoretical calculation.（3）Silicalite-2（S-2）with high skeleton symmetry was synthesized by sol-gel method,and sub-nano Pd particles were confined in S-2 zeolite by in-situ ligand protection method under hydrothermal condition.The pore structure of S-2 zeolite posted steric physical barriers against the migration of Pd NPs.Meanwhile,the strong interaction between active Pd and substrate provides a chemical microenvironment for accelerating the reaction.The chracterization tests and performance evaluation results display that the catalyst（Pd₃@S-2）with Pd NPs size of 1.5 nm has superior catalytic activity for the complete decomposition of FA without additional additives with a TOF value of 2009 h^-1 at 30°C,and has 100%H₂ selectivity,excellent cyclic and thermal stability.In addition,DRIFTS analysis further proves that Pd NPs confined in zeolite can promote the decomposition of FA.