Study On Catalytic Carbon Dioxide Conversion By Bifunctional Metal Complex Catalyst And Alcohol Amine

The high emission of carbon dioxide has a serious impact on the environment,so the conversion of carbon dioxide,as C1 resource,into useful industrial products or their precursors has great research significance.In this paper,the development of high-efficiency catalysts to catalyze the conversion of carbon dioxide is focused on the conversion of carbon dioxide into high value-added chemical products by constructing C-N and C-N bonds,which is of great significance in environmental protection and resource utilization.The specific work content is as follows:1.A series of bifunctional Schiff base metal catalysts（3A-3E）with two imidazole groups was prepared for coupling reaction catalyzed by carbon dioxide（CO₂）and epoxides.The effects of various reaction variables on the catalytic activity were investigated systematically and the optimized reaction conditions were screened as（80°C,1 MPa and 1 h）.The catalyst 3A exhibited exceptionally effective activity with 96%yield and 99%selectivity to propylene carbonate（PO）in the optimized reaction conditions.Meanwhile,this series of catalysts can also catalyze the coupling reaction of CO₂ and other epoxides even under atmospheric pressure.Additionally,the catalyst could be easily reused only with slight loss of activity after five recycles.Moreover,kinetic studies were carried out preliminarily for three metal（3A,3B,3C）catalysts and the formation activation energies（Ea）of cyclic carbonate were obtained.The apparent activation energy Ea c atalyzed by 3B is only 41.11 kJ/mol,while the Ea for 3C is 44.49 kJ/mol and Ea of 3A is 50.85 kJ/mol.The sequence of Ea agrees well with the catalytic activity.Finally,a possible mechanism was proposed,in which the one-component bifunctional catalyst could activate epoxide via the interreaction of M-O and open the ring of epoxide by nucleophilic attack with X^-ions.2.Metal catalysts have the characteristics of high catalytic efficiency,but at the same time,there are problems such as expensive cost and metal pollution.Therefore,we use a seires of cheap and commercial available alcohol amines to achieve chemical conversion of CO₂.Take the cycloaddition of CO₂ and epichlorohydrin（ECH）as model reaction to catalyze N,N-dimethylethanol amine（DMEA）was chosed as the best catalyst.The effects of reaction temperature,time,pressure and catalyst dosage on the catalytic activity were systematically studied.The optimum reaction conditions were screened as follows:110°C,1 MPa,2 h,catalyst dosage 1 mol%（relative to Substrate）.DMEA also can catalyze a variety of end group alkylene oxide and cyclic lactone substrates to react with CO₂ with good to high yield and>99%selectivity even under atomerspheric pressure.The catalyst system is active even after 4continuous use periods and shows good sustainability.Moreover,kinetic studies were carried out preliminarily for three alcoholamines（DMEA,DEEA,DBEA）catalysts and the formation activation energies（Ea）of cyclic carbonate were obtained.The order of was Ea_（DMEA）=26 kJ/mol<Ea_（DEEA）=38 kJ/mol<Ea_（DBEA）=48 kJ/mol.The sequence of Ea agrees well with the catalytic activity.The calculated results were consistent with the experimental results:The better the catalytic effect,the lower the activation energy.Finally,a proposed mechanism was given based on experiments and related literatures.3.In addition to being used as a catalyst for CO₂ chemical conversion via the formation of C-O bonds,DMEA was also proved to be able to construct C-N bonds to achieve CO₂ chemical conversion reactions in the absence of solvent and co-catalyst:（a）The reaction conditions of DMEA dosage,temperature,time and CO₂ pressure were studied by using CO₂ and aziridine as template to obtained the optimum conditions（DMEA 10mol%,110°C,12h,1MPa）.Under the optimal conditions,DMEA can efficiently and selectively convert CO₂ with various nitrogen heterocycles to form 5-substituted oxazolidinone and 4-substituted oxazolidinone;（b）DMEA can also catalyze the formylation of carbon dioxide with amines to form formamides with hydrosilane as reducing agent under the solvent and cocatalyst-free conditions.The cycloaddition of CO₂ and N-methylaniline was studied as template reaction,the effects of temperature,time,CO₂ pressure and phenylsilane dosage on the reaction were studied to obtain the optimal conditions（40°C,24 h,1 MPa CO₂,1 eqv.PHSiH₃）.The catalyst could also efficiently catalyze the formylation reaction of various amines with carbon dioxide to form a variety of substituted formylation products.