The Study On Catalytic Performance Of Modified Sepiolite Supported Palladium Catalyst For Dehydrogenation Of Formic Acid

Hydrogen energy has been considered as the most potential green energy in the21st century due to its high heat value and no pollution,which can substitute fossil energy and solve environmental problems.However,the efficient storage and safe transportation of hydrogen energy hinders the development of hydrogen energy technology.As a liquid at room temperature and pressure,formic acid can be used ass a hydrogen storage material due to the high hydrogen content of 4.4 wt.%,and realize safe storage and stable transportation of hydrogen energy.But at room temperature,formic acid can only decompose to produce hydrogen under cataly sis.In this paper,based on the research in the progress of formic acid dehydrogenation catalysts in the past decade,the supported Pd-based catalysts have been optimized and improved in respect of support and modified support.And the structure-activity relationship and catalytic mechanism of the catalyst have been investigated.In this work,based on the coupling reaction between the silane coupling agent and the inorganic material,modified sepiolite supported Pd catalyst Pd/A-SEP-NH₂was prepared by using natural clay mineral sepiolite as a novel support,and3-aminopropyltrimethoxysilane（APTMS）as the modifying agent with amino functional group.At 30℃,the catalyst can catalyze dehydrogenation of formic acid with 5631 m L g^-1 h^-1(TOF_initial=1354 h^-1),the apparent activation energy of formic acid dehydrogenation reaction in the present of catalyst is 44.5 k J mol^-1.The amine-functionalization of the sepiolite support is beneficial to improve the dispersion of metal particles and form ultrafine Pd nanoparticles.The average particle size of Pd nanoparticles can be as small as 2.8 nm.There is a strong interaction between the amino group and Pd nanoparticles.The amino group changes the electronic structure of Pd,which can effectively improve the catalytic activity of the catalyst.Basic sites abound on the surface of amine-functionalized sepiolite.Particularly,the content of amino basic sites is proportional to the concentration of APTMS,that is,the greater the concentration of APTMS,the more the content of amino basic sites.The amino basic sites accelerate the dissociation of O-H in formic acid molecules,thereby promoting the dehydrogenation of formic acid.The activity of the catalyst shows a volcanic relationship with the content of amino basic site.The optimal content of the amino group is 0.76 NH ₂/g SEP.The content of amino basic sites affects metal Pd loading.The optimal Pd content of the catalyst is 3.5 wt.%.Excessive amino basic sites lead to a decrease in Pd content,which leads to a decrease in catalyst activity.The modified sepiolite supported Pd catalyst was further optimized.The catalytic activity of the Pd/CA-SEP-NH₂catalyst（calcination temperature 600℃）was increased by 30%,and TOF_initial could reaches 2031 h^-1.The catalytic activity of Pd/Zr O₂/CA-SEP-NH₂ catalyst was further increased by 15%,and TOF_initial could reach 2352 h^-1.However,the disadvantage of the catalyst is its poor stability,which needs further improvement.Here,a novel modified sepiolite supported Pd catalyst for formic acid dehydrogenation is developed.The catalyst can efficiently catalyze the dehydrogenation of formic acid,and the cost is low,which can lead a new avenue for cost effective hetergeneous formic acid dehydrogenation catalyst.