Construction Of Zeolite-like Imidazolate Framework Materials And Their Catalytic Formylation Of CO₂ With Amine

Since the second industrial revolution,the extensive use of fossil energy such as coal and oil has led to a continuous increase in the total amount of global CO₂,causing serious greenhouse effect and environmental pollution.From the perspective of sustainable development,the use of cheap,green,renewable CO₂as a C1 raw material to synthesize high value-added chemicals is of great significance for environmental and energy mitigation.Among them,amide compounds are important chemical raw materials and solvents widely used in pesticides,pharmaceuticals and other fields.Therefore,the research on N-formylation of amines with CO₂is the most concentrated.Aiming at the problems of poor stability,strong corrosivity,high production cost and complex preparation of catalysts used in the N-formylation reaction system of CO₂participation.In this paper,based on the preparation of simple,green and adjustable zeolite-like imidazolate framework material ZIF-90,a carboxylic acid functionalized ZIF-90-C catalyst was constructed and used to efficiently catalyze the N-formylation of CO₂.The specific work is as follows:（1）Based on ZIF-90,the carboxylic acid functionalized ZIF-90-C₁catalyst was obtained by H₂O₂oxidation.Its morphology and internal structure were characterized by SEM,TEM,FT-IR,XRD,XPS and other modern analytical techniques,which further confirmed the successful construction of the active site（carboxyl）.The test of catalytic activity showed that ZIF-90-C₁could effectively catalyze the N-formylation of morpholine at the reaction temperature of 50℃,reaction time of 24 hours,and Ph Si H₃of 0.5 mmol,with the conversion of 100%and the yield of N-formylmorpholine of 94%.Theoretical calculations show that firstly morpholine and ZIF-90-C₁generate active site-COO^-in situ,then Ph Si H₃and CO₂are activated to form aldehyde silane,and finally morpholine is subjected to nucleophilic attack to obtain N-formylmorpholine.Most importantly,the energy of ZIF-90-C₁promoted CO₂hydrogenation to the key intermediate aldehyde silane is 25.3 kcal/mol,which is much lower than 47.5 kcal/mol without catalyst.In addition,kinetic experiments show that the key step of CO₂silicic acid hydrogenation can be simplified as a pseudo-first-order reaction at high CO₂concentration.At 50℃,the reaction rate constant(k_obs)is 0.08899 h^-1,and the apparent activation energy（Ea）is 35.7 k J mol^-1.Finally,ZIF-90-C₁showed high recyclability in the N-formylation reaction,and the catalytic performance almost did not decrease during 5 cycles.（2）Photocatalysis is in line with the current sustainable development theme due to its green,renewable,low energy consumption and other characteristics,which is of great significance for the preparation of catalysts.Therefore,on the basis of（1）,we prepared ZIF-90-C₂catalyst by simple photocatalytic method,which effectively reduced the energy consumption in the process of catalyst preparation.The reaction parameters were optimized.Under mild conditions（45℃,12 h）,the conversion of benzylamine was100%,and the yield of N-formylbenzylamine was 83%.The mechanism of in situ catalytic reaction was verified by ¹³C labeling control experiment and the analysis of the key intermediate formoxysilane.（3）On the basis of（2）,we further designed the mesoporous zeolite-like imidazolium ester framework ZIF-90,and then prepared the carboxylic acid functionalized ZIF-90-C₃through a simple oxidation method.Its surface morphology and structure were characterized by FT-IR,XRD,SEM,TEM and BET,and its catalytic activity and stability were studied.Under the optimal reaction conditions,it can catalyze the N-formylation of various amines and has high catalytic activity.