CO₂ Adsorption And Electrochemical Performance:Cobalt Carbonyl Clusters And Re-Cobalt Carbonyl Clusters Bridged Cluster Compounds As Precursors

With rapid economic development,industrial emissions and waste burning have greatly exacerbated the carbon emission problem.At present,more than 130countries and regions have proposed the“zero carbon”climate target,CO₂emissions have brought great challenges to human survival and development.Therefore,the development of effective CO₂capture technology to reduce atmospheric CO₂emission concentration is the key to solve environmental problems.Metallic carbonyl clusters have become the focus of recent research due to their unique advantages such as stable skeleton composed of multiple metal-metal bonds and abundant metal adsorption sites.However,the carbonyl ligand in cobalt carbonyl clusters has weak interaction with metal.After low temperature pyrolysis,the carbonyl ligand in the skeleton can be completely removed,while the remaining metal-metal skeleton structure not only does not collapse,but also exposes all metal adsorption sites.As the most common CO₂trapping material,most of the metal-organic framework materials（MOFs）try to expose the unsaturated active site by the departure of guest molecules,but cause the collapse of the structure,thus affecting the adsorption function of gas.In addition,carboxyl functional groups are easy to form strong coordination bonds with metal ions,which can greatly improve the stability of materials.Therefore,the synthesis of carboxy-containing materials that fully expose the coordination unsaturated metal sites is of great significance for CO₂capture.In this paper,cobalt carbonyl clusters containing carboxyl functional group s and trifluoroacetate containing rare earth metals were selected as raw materia ls to design and synthesize efficient adsorption materials and cobalt-based catal ysts,and the effects of rare earth metal types,introduction methods and the st ructural properties of complexes on CO₂adsorption performance were studied.By calcination of cobalt carbonyl clusters,cobalt-based catalysts containing car boxyl functional groups with good stability were prepared.Under different exp erimental variables,the optimal reaction conditions of cobalt-based catalysts for ammonia synthesis by nitrate reduction were explored.The main research con tents are as follows:1.Cobalt carbonyl clusters（CO）₆Co₂CC（COOH）₂（1）,（CO）₉Co₃CCOOH（4）,（CO）₁₀Co₄HCCCOOH（7）and trifluoroacetate containing rare earth metals（Ln=Ce,La）combine Ce₁₂[Co₂（CO）₆CC（COO）₂]₈（CH₃COO）₄（CF₃COO）₁₆·16H₂O（2）、La₁₂[（CO）₆CC（COO）₂]₈（CH₃COO）₄（CF₃COO）₁₆·16H₂O（3）、Ce₂{OOCCCo₃（C O）₉}₂{OOCCF₃}₄{（CO）₉Co₃CCOOH}₄（5）、La₂{OOCCCo₃（CO）₉}₂{OOCCF₃}₄{（CO）₉Co₃CCOOH}₄（6）、[Co₃（CO）₉μ₃CRCOOLn₃（μ-OOCCF₃）₆（THF）₃]₂Co（OH）₃}·2THF（8）、{[Co₃（CO）₉μ₃CRCOOLn₃（μ-OOCCF₃）₆（THF）₃]₂Co（OH）₃}·2THF（9）The refer ence adsorption material Co_x+Ln was prepared by mechanically mixing cobalt carbonyl clusters with trifluoroacetate containing rare earth metals.To the prep aration of materials under mild conditions completely carbonyl process,by ther mogravimetric analysis（TG）,in situ infrared spectroscopy（DRIFTS）and temp erature programmed CO₂stripping（CO₂-TPD）,XPS X-ray photoelectron spectr oscopy analysis（XPS）characterization methods of carbonyl off after material s tructures and properties are analyzed,and the CO₂adsorption performance rese arch.The adsorption performance of CO₂was studied.The results show that t he Co _X-Ln complex with definite structure has better CO₂adsorption performa nce than the Co_x+Ln material with mechanical mixing mode.The bridged rare earth metal complexes of Co _X-Ce are superior to Co _X-La complexes in CO₂a dsorption performance.2.Using cobalt carbonyl cluster（CO）₆Co₂CC（COOH）₂,（CO）₉Co₃CCOOH a nd（CO）₁₀Co₄HCCCOOH as precursors,a series of cobalton-based catalysts con taining carboxyl groups were prepared by thermal decomposition method,and t he electrocatalytic study of ammonia synthesis by nitrate reduction was carried out.The influence rule of nitrate removal and catalytic reaction of ammonia synthesis was revealed by cathodic potential,ph of electrolyte and initial conce ntration of NO₃^-.It was shown that the catalyst Co₃COOH-140 was tested und er optimal reaction conditions of-1.05 V vs.RHE potential,electrolyte p H of7 and initial concentration of NO₃^-of 1000 ppm for 2 h.The ammonia yield was found to be 4871.8μg h^-1mg^-1_cat,Faraday efficiency（FE）of 71%and a mmonia selectivity of 60%.The Co₃COOH-140 catalyst showed 41%removal of nitrate.In addition,the catalyst was tested for 10 h of cycling stability,an d the nitrate removal rate reached 98%when the reaction proceeded to 8 h.And NO₂^-was rarely detected after electrocatalytic reduction throughout the ex perimental investigation,further indicating a high selective reduction of nitrate to ammonia.