Novel Functionalized Metal-organic Frameworks For Catalytic CO₂ Hydrogenation To Formic Acid

An escalating rate of fossil fuel combustion produces a large amount of carbon dioxide（CO₂）,which leads to the serious problem of global warming.Therefore,selective conversion of CO₂into useful fine chemicals is required to reduce CO₂ emissions.Formic acid is a non-toxic and non-flammable liquid at room temperature,which is a promising hydrogen storage material among several fine chemicals from CO₂ conversion.Therefore,the hydrogenation of CO₂ to formic acid has important research value.The hydrogenation of CO₂to formic acid requires efficient catalysts.At present,homogeneous catalysts have been widely studied and exhibited high catalytic performance in the hydrogenation of CO₂ to formic acid.However,homogeneous catalysts are difficult to recover and reuse.The traditional heterogeneous catalyst has the problem of low activity.Hence,novel and efficient heterogeneous catalysts for the hydrogenation of CO₂ to formic acid has attracted extensive attentions.Recently,metal-organic framework（MOF）was found to be a very important carrier or heterogeneous catalyst due to its special physical and chemical properties.In this thesis,homogeneous iridium complexes with high catalytic activity were loaded into MOF to construct novel functionalized MOF catalytic materials,which showed high catalytic activity and recyclability for the CO₂ hydrogenation reaction.Meanwhile,the catalytic reaction conditions were optimized,the catalytic activity and reusability of various catalysts were tested,and the reaction mechanism was proposed.（1）A series of functionalized MOF catalysts supported by iridium complexes was designed and synthesized,and their structures and morphology were characterized by ¹H NMR,IR,TGA,XRD,SEM,ICP-MS,XPS and BET.（2）The activity and reusability of functionalized MOF catalysts for CO₂ hydrogenation were tested.Cat2,Cat3,and Cat6 were found to be superior in catalytic activity.In addition,the effects of reaction conditions such as catalyst loading,temperature,pressure,reaction time and additive base on catalytic performance were explored with Cat2,Cat3 and Cat6.The results showed that MOF catalysts Cat3 provided the best activity.At 80℃,3.0 MPa H₂/CO₂（1:1）,catalyst loading 10 mg,8 m L anhydrous ethanol,and 5 mmol K₂CO₃,the TON reached6734 after 24 h.Cat3 was among the best heterogeneous MOF catalysts currently reported for the hydrogenation of CO₂ to formic acid.Under the experimental conditions,Cat3 can be reused at least four times,and the total TON using five times is 19582.（3）Cat3 was used to explore the reaction mechanism of CO₂hydrogenation to formic acid.A possible reaction mechanism with metals and ligands cooperation was proposed.In this thesis,we designed and synthesized a series of novel MOF supported iridium complexes for CO₂ hydrogenation to formic acid.Meanwhile,the reaction mechanism was explored.This study provided new ideas for the design and development of novel MOF catalyst for CO₂ hydrogenation.