Catalytic Hydrogen Generation From Formic Acid Over Metal-organic Frameworks

Fossil energy plays an important role in the continuous development of society,and people’s demand for fossil energy is increasing year by year.However,the environmental pollution caused by the massive consumption of fossil energy and the limited reserves of fossil energy have gradually emerged.Therefore,the development of new clean energy has become one of the global focus issues.Among them,hydrogen energy is regarded as a promising clean energy.At present,to solve the problem of hydrogen source and achieve high-efficiency hydrogen production with low cost is the main direction that scientific research workers strive for.In this paper,certain active components were introduced in several metal-organic frameworks（MOFs）,and the catalysts were used in the hydrogen production from formic acid.Formic acid is a byproduct in the process of biomass conversion,and efficient decomposition of formic acid can make the process of biomass high value utilization more economical and environmental friendly.Firstly,MOF-101-2 was synthesized by acylation-coordination reaction on the support of NH₂-MIL-101（Al）.Then,MOF-101-2 was used in the hydrogen production system of formic acid aqueous solution.The influence of the amount of Ir loaded in MOF-101-2,catalyst dosage,initial concentration of reactant and reaction temperature on the hydrogen production process of formic acid was explored.It was found that the hydrogen generation efficiency of the system was the best when 60 mg 15%Ir MOF-101-2 was used to catalyze 2 mol/L formic acid aqueous solution at 50℃.Under the optimal conditions,the catalytic activity of MOF-101-2 was better than that of many heterogeneous catalysts.The TOF_initialof the reaction reached 331.6 h^-1,and the apparent activation energy was as low as 25.22 k J/mol.Meanwhile,the conversion of formic acid was as high as 88%,and the selectivity of hydrogen was close to 100%（CO<10 ppm）.Then a series of Pd supported heterogeneous catalysts Pd/MOFs were synthesized using NH₂-MIL-101（Cr,Al,Fe）as the supports.10%Pd/MOF-Cr（18）catalyst with high catalytic activity and hydrogen production selectivity was obtained through screening.The effects of catalyst dosage,reactant concentration and reaction temperature on the hydrogen production from formic acid were studied.The results showed that at 50℃,when the amount of 10%Pd/MOF-Cr（18）catalyst was 80 mg and the initial concentration of formic acid was 1 M,the performance in hydrogen generation is the best.Under this conditions,the corresponding formic acid conversion was 97.73%,and the selectivity of hydrogen was close to 100%（CO<10 ppm）.What’s more,the TOF_midwas as high as 537.8 h^-1.Finally,in order to reduce the cost of catalyst preparation,NNM-Pd heterogeneous catalysts Ni Pd/MOF-Cr with NH₂-MIL-101（Cr）as support were synthesized,and the effects of catalyst synthesis method,types of non-noble metal precursors,Ni content and Pd loading amount in catalyst on hydrogen generation from formic acid were investigated.The experimental results revealed that when 5 mmol FA（1 M,5 m L）was catalyzed by 80 mg 10%Ni_0.4Pd_0.6/MOF-Cr（OV）at 50℃,the TOF_midof the reaction was as high as 737.9 h^-1,and the conversion of formic acid and the selectivity of hydrogen were close to 100%.At the same time,the catalytic activity of the alloy catalyst did not decrease significantly when it was recycled for three times.