Design And Synthesis Of Nitrogen-Containing Heterocyclic Porous Organic Polymers For Catalytic Conversion Of Greenhouse Gases

Massive greenhouse gas emissions such as CO₂ and CH₄ have accelerated the“greenhouse effect”in recent years and have resulted in a variety of adverse environmental impacts.Developing of catalytic systems to convert CO₂ and CH₄ into fine petrochemicals,value-added chemicals,and clean fuels is a practical approach to alleviate the“greenhouse effect”and simultaneously achieve economic benefits.Porous organic polymers（POPs）is a class of advanced novel functional polymers with low density,high stability,adjustable composition,and easily functionalization,which is believed to be an ideal candidate for catalytic conversion of CO₂ and CH₄.Therefore,the study of using it as a heterogeneous catalyst has attracted wide attention.Despite recent progress in the development of using POPs as catalysts for greenhouse gas conversion,most of the POPs catalysts still suffer from its low catalytic efficiency,strict reaction conditions,complex synthesis and etc.To address this challenge,a series of POPs bearing N-heterocycles were tailored,fabricated,and systematically investigated in this dissertation.The catalytic activity of these POPs was investigated,and the correlation between the activity and composition/porous characteristics was established.The main contents of the dissertation are summarized below.1.Two novel ionic polymers（IPs,namely IP-1 and IP-2）with excellent physiochemical stability were synthesized through a one-pot reaction of 1,3,5-tris（bromomethyl）benzene with 1,4-diazabicyclo[2.2.2]octane and 3,6-di（1H-imidazol-1-yl）pyridazine,respectively,with high yield.Their catalytic abilities to convert CO₂ into cyclic carbonates have been explored,and both IP-1 and IP-2 show excellent catalytic activity under solvent-free,co-catalyst-free,and mild reaction conditions,and can be recycled and reused for six times without decreasing their catalytic abilities.These materials are easily synthesized,and there are no metals and other additives during the catalytic process,which provides a possibility for the industrial immobilization of CO₂ to carbonate over heterogeneous catalysts.2.A new bifunctional cationic polymer CalCOP-1,which is composed of calixarene containing hydroxyl group and imidazolyl group,is synthesized.The experimental results show that the polymer can efficiently convert CO₂ into valuable cyclic carbonate under solvent-and co-catalyst-free conditions,while catalytic activity remains good after several recovery cycles.With abundant phenolic hydroxyl groups as hydrogen bond donors and bromine ions as nucleophiles,the polymer has excellent catalytic activity for converting epoxide into cyclocarbonate.This work not only presents a new method for the synthesis of competitive green heterogeneous catalysts but also provides an example for the synthesis of cyclocarbonates by CO₂ cycloaddition reaction catalyzed by ionic polymers containing calixarene for the first time.Our study offers a new approach to the development and preparation of supramolecular-based organic polymer materials featuring functional sites as green catalysts for efficient CO₂ utilization.3.Inspired by the design principle of homogeneous catalyst,hyper-cross-linked polymer（HCP）with Pd single site coordinated to N of HCP is synthesized and used for heterocatalysis of CH₄.This novel Pd-POP catalyst could efficiently convert CH₄ to methanol under mild conditions（80°C,30 bar）and avoid over-oxidation of the product.The catalyst exhibits the highest（turnover number,TON）value 1276 among the reported results.The excellent activity of the catalyst can be attributed to the following reasons:1)The porous feature of the catalyst enables the enrichment of CH₄ near the catalytic active sites,and the Pd-containing polymer catalyst has a high affinity to CH₄,as verified by the Q_st calculation.2)The agglomeration of the Pd species is avoided due to the highly dispersed nature of the catalyst.The novel catalyst can be produced utilizing a simple synthetic procedure using low-cost materials.Furthermore,the novel catalyst also has excellent recyclability without performance loss.The results obtained in this research could provide useful guidance for the future design and synthesis of CH₄ activation catalysts.