Controllable Preparation And Mechanism Study Of Crystalline Porous Framework-based Catalytic Materials

In recent years,the energy crisis and the large amount of greenhouse gas emissions have become the major challenges facing the world.Among them,developing green renewable energy and realizing the recycling of carbon resources have become two effective candidates.Under the action of catalysts,the decomposition of water into H₂ and the reduction of greenhouse gas CO₂ into carbon-based fuels with high added value have also been the research hotspots in the field of energy and environmental science in recent years.Metal organic framework?MOFs?and covalent organic framework?COFs?have the specific surface area and concreted complete structure can be designed,have been widely used in the field of catalysis,but at present,based on MOFs and COFs catalyst,the catalytic center of the building and system regulation and to explore different active center on catalytic activity of the system is not perfect enough.Based on the above analysis,three new types of crystalline porous frame-based catalytic materials were prepared in a controllable manner in this paper.Through the regulation of the catalytic activity center,the activity of materials in energy catalytic conversion was improved,and the catalytic mechanism was further studied.The detail research content is as follows:?1?A series of Ni?OH?₂-X%/Tp Pa-2 composites dispersed in the active center were constructed by the strategy of in situ controllable synthesis,and the photocatalytic activity of the composites was further regulated by controlling the content of Ni?OH?₂.The results of photocatalytic experiments showed that Ni?OH?₂-X%/Tp Pa-2 showed the optimal activity of photocatalytic hydrogen production was 1895.99?mol·h^-1·g^-1,which was 26.3 times that of Tp Pa-2 alone.In addition,its catalytic activity was similar to that of Tp Pa-2 supported by 0.3 wt%Pt as a co-catalyst.Finally,after light catalytic reaction product and charge transfer dynamics analysis shows that Ni?OH?₂-X%/Tp Pa-2 composite material as catalyst in the initial stage of Ni?OH?₂ is back into elemental Ni,by means of elemental nickel super electronic transmission performance lead to system to effectively transfer,and Tp P-2 as elemental nickel and Ni?OH?₂ dispersion carrier,and then in the Ni/Ni?OH?₂/Tp Pa-2 within the ternary compound system of photocatalytic decomposition of hydrogen activity promotion.?2?Using Fe₂M??₃-O??CH₃COO?₆)?Fe₂M?cluster with adjustable central metal as metal source,a series of MOFs?PCN-250?based catalytic materials with the same framework but different central transition metals were constructed.In the presence of ruthenium bipyridinium as sensitizer,different frameworks have been used to regulate the activity and selectivity of CO₂ reduction.The results of photocatalytic experiments show that the activity and selectivity of photocatalytic CO₂ conversion into CO are better than that of unregulated single metal PCN-250-Fe₃ by regulating the hetermetal PCN-250-Fe₂M.In particular,PCN-250-Fe₂Mn showed the highest photocatalytic CO₂ reduction activity of 21.51 mmol·h^-1·g^-1,much higher than that of single metal PCN-250-Fe₃(13.45 mmol·g^-1·h^-1).Charge transfer kinetics and DFT theoretical calculation show that the metal center control framework,the introduction of a second metal ions can promote the photoproduction electronic migration to the active sites,and by promoting the formation of CO₂ reduction reaction intermediate state and suppress the generation of hydrogen generation of intermediates to improve for CO₂ adsorption and activation,so as to realize the activity of ascension.?3?The controlled growth of porphyrin COFs?Por-COF?on carbon nanotubes was realized by covalent bonding connected,and the transition metal ion M?M:Co,Fe,Ni?was further re-complexed.The catalytic activity of MWCNT-Por-COF-M was regulated by regulating different catalytic metal centers.The results of electro-catalytic experiments show that MWCNT-Por-COF-Co shows the best reduction activity in CO₂ conversion into Co,and the maximum CO Faraday efficiency can reach 99.3%?-0.6V vs.RHE?.And in a wide electric potential range of-0.6?-0.9 V vs.RHE,over 90%Faraday efficiency is achieved.In addition,MWCNT-Por-COF-Co demonstrated a high conversion frequency of 70.6 s^-1?-1.0V vs.RHE?and a high electrochemical persistence?50 h?.Finally,carbon nanotubes are proved to be efficient electron transport channels in CNT.And MWCNT-Por-COF-Co showed better CO₂ adsorption and activation.