Design And Preparation Of Pd-UiO MOFs Catalyst And Performance For Catalytic Tandem Hydrogenation And Esterification Of Carbon Dioxide To Ethyl Formate

Global economy growth,especially in the developing countries,has led to global carbon dioxide(CO2)emissions reaching several ten billions of tons per year.To mitigate the concern with greenhouse gas emissions such as CO2,sustainable conversion of CO2 to fuels/chemicals has received increasing attention,especially considering CO2 is non-toxic,non-flammable,and abundant Ci resources.Among the potential products considered from CO2,ethyl formate(HCOOEt)is a stable platform chemical,which is widely used in organic synthesis for,pharmaceutical,food and perfume industries.CO2 can be possibly converted to HCOOEt via tandem steps:(1)hydrogenation of CO2 to formic acid;(2)esterification of formic acid with ethanol(EtOH).The first step of CO2 hydrogenation can be catalyzed by metal nanoparticles such as Pd nanoparticles(Pd NPs)and the second step of esterification is typically catalyzed by acid sites.In addition,base or basic sites for CO2 adsorption can promote the reaction of carbon dioxide hydrogenation.Metal-organic frameworks(MOFs)are a class of hybrid materials with well-defined structures,which can serve as a suitable platform to arrange multiple and functionally distinct catalytic centers within the same structure.Specifically,metal nodes can act as catalytic active sites for catalytic reactions.Catalytic active sites can be introduced by functionalizing the ligand.Metal nanoparticles in the pores of the MOFs can catalyze the reaction.The main work of this paper is to use MOFs as a platform to design and synthesize multifunctional catalysts for catalytic tandem hydrogenation and esterification to directly carbon dioxide to ethyl formate.The main research is summarized as follows:1.The functional ligand H2L(H2L = PdCl2(H2bpydc))was prepared by chelating Pd2+with H2bpydc(H2bpydc = 2,2'-bipyridine-5,5'-dicarboxylic acid)ligand.UiO-Lx/bpdc6-x was prepared by solvothermal method with H2L and H2bpdc(H2bpdc=4,4'-biphenyl dicarboxylic acid).Pd(z)-UiO-bpydcx/bpdc6-x was prepared after reduction treatment with NaBH4.XRD,IR,SEM,TEM,1H NMR characterization results show that this MOF had the same morphology and structure as that of UiO-67 MOF(only H2bpdc ligand).Pd NPs as well as basic ligand(bpydc)and acidic metal node owned Pd(z)-UiO-bpydcx/bpdc6-x can act as catalytic active sites.Pd NPs can catalyze CO2 hydrogenation to form formic.Acidic metal node[Zr6(?3-O)4(?3-OH)4(CO2)12]catalyze the esterification of formic acid and EtOH to HCOOEt.Basic ligand(bpydc)for adsorbing CO2 can promote the reaction of CO2 hydrogenation.The Pd(1)_UiO-bpydc1/bpdc5 exhibited a high activity in converting CO2 to form HCOOEt with a production rate of 1333 ?mol/gcat/h at 135? and a pressure of 4 Mpa(H2/CO2= 3/1)for 10 h or a turnover number(TON)of 475.2?UiO-66,UiO-66-NH2 and UiO-66-bdc3/(bdc-NH2)3 were prepared by solvent thermal method with H2bdc(H2bdc = terephthalic acid)and H2bdc-NH2(H2bdc-NH2=2-amino terephthalic acid).Pd-UiO-66,Pd-UiO-66-NH2 and Pd-UiO-66-bdc3/(bdc-NH2)3 were prepared by impregnation with H2PdCl4.XRD,IR,SEM,TEM characterization results show that these MOFs contain Pd NPs,basic ligand(bdc-NH2,except Pd-UiO-66)and acidic metal nodes.Similar to Pd(z)-UiO-bpydcx/bpdc6-x,Pd NPs can catalyze CO2 hydrogenation to form formic;acidic metal node catalyzes the esterification of formic acid and ethanol(EtOH)to HCOOEt;basic ligand(bdc-NH2)for adsorbing CO2 can promote the reaction of CO2 hydrogenation.HCOOEt formation rate on Pd-UiO-66-NH2 reaches 937 ?mol/gcat/h at 135 ? and a pressure of 4 Mpa(H2/CO2= 3/1)for 10 h.In addition,methanol was also produced with a formation rate of 607?mol/gcat/h.