Preparation And Characterization Of Pd-Co/C Catalyst And Its Catalytic Activity For Hydrogen Production From For Mic Acid Decomposition

Formic acid（FA）is a promising chemical hydrogen storage material due to its nontoxic,stable properties and wide sources.However,how to release hydrogen from FA efficiently and stably is a difficult problem for scholars.Studies have shown that the key to hydrogen production from formic acid decomposition is the catalyst,and among many catalysts for hydrogen production from formic acid,Pd-based catalysts have received extensive attention.However,Pd is a precious metal,and the expensive Pd leads to high cost of catalysts,which limits its industrial application.Therefore,it is of great significance to select non-noble metals as additives,reduce the amount of Pd,and select the appropriate carrier to highly disperse Pd on the carrier to assemble the supported Pd-based catalysts,so as to provide catalysts with application prospects for the study of hydrogen production from formic acid and promote the development of hydrogen energy.In this paper,a series of supported palladium-based catalysts were prepared by impregnation method.The effects of support and additives on the structure of palladium-based catalysts and their catalytic performance for formic acid hydrogen production were studied.By comparison,XC-72 carbon black was selected as the carrier of the catalyst,and cobalt was used as the catalyst promoter to prepare Pd_0.9Co_0.1/C₆₅₀ catalyst.The structure of the catalyst was characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,specific surface area and pore structure analysis,and a series of meaningful research results were obtained.Work.（1）In the carrier selection,the catalytic activities of Pd-supported catalysts on uncalcined XC-72 carbon,C₆₅₀,silica sol,carbon nitride,CNT and ZIF-67 were compared.Studies have shown that among the Pd catalysts supported on the above supports,Pd/C（XC-72）has the highest activity,and the catalytic performance of XC-72 carbon black is higher after calcination at 650°C(marked as C₆₅₀).Therefore,XC-72 carbon black is the appropriate support for Pd-based catalysts for the decomposition of formic acid to hydrogen.The catalytic activity of formic acid on Pd/C₆₅₀ catalyst reached 7257 h^-1 at 333K.Through structural characterization,it was found that the oxygen content on the surface of XC-72 carbon black changed before and after calcination.The oxygen content of Pd/C₆₅₀ catalyst after calcination was higher than that of uncalcined Pd/C catalyst.The oxygen-containing groups on the surface of the support may have a synergistic effect on promoting the decomposition of formic acid to produce hydrogen,thereby improving the activity of the catalyst.Studies have shown that amino additives can promote the activity of catalysts,and 3-aminopropyltriethoxysilane（APTS）is the suitable additive for the preparation of catalysts.（2）In the screening of additives,through comparison,cobalt has good catalytic effect.Compared with Pd/C₆₅₀ catalyst,after adding Co element,the usage of noble metal Pd was reduced,and Pd_0.9Co_0.1/C₆₅₀ catalyst with good activity was prepared.The addition of Co element makes the particle size of Pd metal smaller and improves the activity of the catalyst.The smaller the particle size of Pd nanoparticles,the more active sites,and better contact with formic acid.In summary,after the addition of non-precious metal Co,Pd-Co alloy was formed,which reduced the particle size of Pd nanoparticles and formed more active sites,thus promoting the catalytic decomposition of formic acid to hydrogen over Pd-based catalysts.（3）The contents of Pd⁰ and Pd²⁺in Pd/C₆₅₀ catalyst,Pd_0.9Co_0.1/C₆₅₀ catalyst and Pd_0.9Co_0.1/C_650（10）catalyst were analyzed by XPS.It was found that the higher the ratio of Pd²⁺/Pd⁰,the better the catalytic performance of the catalyst for formic acid to hydrogen.Among them,after the addition of non-precious metal Co,the Pd²⁺/Pd⁰ ratio of Pd_0.9Co_0.1/C₆₅₀catalyst increased,and the catalytic performance was also better than that of Pd/C₆₅₀ catalyst.However,after 10 times of formic acid decomposition over Pd_0.9Co_0.1/C_650（10）catalyst,the ratio of Pd²⁺/Pd⁰ in Pd_0.9Co_0.1/C_650（10）catalyst decreased,the content of Pd²⁺decreased,and the catalytic performance for formic acid to hydrogen decreased by 44.7%.In addition,the catalytic activity of Pd_0.9Co_0.1/C₆₅₀ is 8117 h^-1 at 333 K in FA/SF solution(n _FA/n _SF=1:2;FA,3 mmol;n _Pd/n _FA=0.02),which is much higher than the reported hydrogen production rate.The activation energy of hydrogen production from formic acid was calculated by Arrhenius equation.It can be seen from the comparison that after the addition of non-precious metal Co,the apparent activation energy of Pd/C₆₅₀ decreased from 52.43 k J/mol to 47.73 k J/mol of Pd_0.9Co_0.1/C₆₅₀ catalyst,indicating that the introduction of Co reduced the activation energy of formic acid decomposition to hydrogen production,thereby improving the hydrogen production activity of the catalyst.