Construction Of The New Catalytic Systems For The Application In The Conversion Of Acidic Gases

Carbon dioxide(CO2)is one of the main greenhouse gases.It can also be used as an abundant and green renewable Cl resou,rce.In the past decade,CO2 chemistry has attracted significant attention in the field of green chemistry from the scientific community 'thanks to global warming.Observably,the conversion of CO2 into value-added product is full of challenges due to the thermodynamic stability and kinetic inertness of CO2.The activation and transformation of CO2 is one of the core contents of this paper.At the same time,sulfur dioxide(SO2)is a typical atmospheric pollutant.The increasing emission of SO2 from the burning of fossil fuels has drawn much attention because it is a significant source of atmospheric pollution that threatens the environment and human health.The development of highly efficient and green absorbents to capture and convert SO2 into value-added chemicals is another scientific challenge.In this paper,we focus on the transformation of CO2 and SO2.Firstly,we review the main methods of chemical conversion of CO2 and SO2.Then related research works are carried out about the activation of CO2 and subsequent conversion.Furthermore,we have also developed the new methods for the SO2 capture and it's in situ conversion using ionic liquids.The specific research contents are as follows:(1)The reduction of CO2 into formic acid or its conjugate base using H2 is an attractive process.The hydrogenation of CO2 requires the activation of both H2 and CO2 at the same time.It makes this reaction full of challenges because both H2 and CO2 are extremely stable.We report a catalytic system involving a stable cycloalkyl(amino)carbene copper hydride that activates CO2,working in tandem with a Lewis pair of B(C6F5)3 and DBU that heterolytically splits H2.Surprisingly,through a combination of stoichiometric and catalytic reactions,the classical Lewis pairs outperform frustrated Lewis pairs in this process.The results provide an important theoretical reference for the design of CO2 hydrogenation catalyst,and also enrich the application of low-cost metal copper in the field of CO2 hydrogenation reaction.(2)Hydrogenation of CO2 to formate with H2 in the absence of transition metal is a long-standing great challenge in catalysis.We demonstrate a transition metal-free catalytic process for the CO2 hydrogenation to formate with H2 catalyzed by B(C6F5)3/M2CO3(M=Na,K,and Cs),affording an unprecedented TON value of 3941.The reactions between B(C6F5)3 and K2CO3 are found to form a Lewis pair of K2[(BCF)2-CO3]that can react with both H2 and CO2 to produce formate.Further researches reveal that the Lewis pair enables the splitting of H2 and the insertion of CO2 into the B-H bond.This work enriches the Lewis pair in the catalytic field and provides a transition metal free strategy for the catalytic hydrogenation of CO2.(3)The development of CO2 reduction under mild conditions is highly desirable.BH3NH3,as an excellent hydrogen storage material,has excellent water solubility and reducing property.We demonstrate a scheme of CO2 reduction to formate with BH3NH3 in water under mild conditions without any catalysts.Solvent water is found to work as a reactant for the reduction of CO2 with BH3NH3 to the formate.Furthermore,the addition of base can significantly increase the yield of formate via formation of bicarbonate intermediate,in which DBU shows the best performance.(4)Since BH3NH3 is capable of reducing CO2 to formate,we continue to study the activation and conversion of CO2 under mild conditions.We thus develop a green,catalyst-free and effective procedure for the N-formylation using CO2 as the C1 source and BH3NH3 as the reductant under mild conditions for the first time.The mechanism research indicates that the intermediate of formate can be formed during the reduction of CO2 with BH3NH3 in DMF,which can further react with amine to formamide.The corresponding formylated products of both primary and secondary amines can be obtain in good to excellent yields(up to 96%of isolated yield)under mild conditions.(5)The direct synthesis of dimethyl carbonate(DMC)from CO2 and methanol is another sustainable pathway of CO2.Usually,the formation of DMC can be promoted by using dehydrating agent.We demonstrate imidazole hydrogencarbonate ionic liquids([CnCmIm][HCO3])as recyclable catalysts and dehydrating agents for the catalytic synthesis of DMC from CO2 and methanol under mild conditions.Experimental and theoretic results reveal that[CnCmIm][HCO3]can quickly transform into a CO2 adduct.The latter serves as effective catalyst and dehydrant.The ionic liquid can be reused easily without obvious loss on its catalytic and dehydrating ability.(6)Ether-functionalized ionic liquids have high SO2 absorption capacity.However,these ionic liquids generally have high price and viscosity,and the preparation processes are cumbersome.We demonstrate an innovative strategy for SO2 capture and fixation to cyclic sulfites in dual ether-functionalized protic ionic liquids(PILs)for the first time.These dual ether-functionalized PILs exhibit low viscosity and remarkable SO2 loading capacity.Particularly,the SO2 absorbed in the PILs can be directly transformed into cyclic sulfites without any additives.Furthermore,these dual ether-functionalized PILs are also used as efficient catalysts for the synthesis of a series of cyclic sulphites using equimolar SO2 and epoxides.This innovative strategy not only eliminated the traditional intensive energy input for SO2 desorption but also enabled the production of value-added cyclic sulfites.(7)An innovative strategy for sustainable SO2 capture and conversion in novel imidazole-based deep eutectic solvents(DESs)is demonstrated in this work.These DESs exhibit an extremely high SO2 loading capacity(up to 1.39 g/g)and excellent reversibility.The absorbed SO2 can be rapidly converted in situ to sulphurin the presence of H2S at room temperature without any additives.We believed that imidazole-based DESs provide a potential opportunity for the green and sustainable SO2 capture and conversion.