Cucurbit[n]urils Supported Keggin–type Heteropoly Acids And The Properties Of Research

Due to its unique structure and excellent catalytic performance,Heteropoly acids?HPAs?has become one of the hotspots in research of inorganic chemistry.Heteropoly acids compounds?including heteropoly acid and heteropoly acid salt?have a strong acidic and redox properties.With the character of homogeneous phase and heterogeneous catalysis in the reaction,they are widely used in all kinds of organic catalytic reaction,such as esterification,etherification,aceto–xylation,alkylation,polymerization,hydration dehydration,etc.HPAs with keggin structure are widely used as acid catalysts due to their novel structural properties and very strong Br?nsted acidity.However,with less surface area,heteropoly acid catalytic activity is not able to give full play in the reaction.Besides,HPAs is soluble in water and organic solvents,so it is hard to separate it from the reactant solution.Therefore,the supported–HPAs study has become more important.Porous materials with large surface areas such as Si O₂,ZrO₂,activated carbon and zeolite are often used to support HPAs.But the force between HPAs and the support is weak and unstable.Cucurbit[n]urils?Q[n]?,is a kind of novel macrocyclic cage supramolecular compounds.The port of carbonyl with obvious negative charge and hydrophobic cavity where small organic molecules can be packed,leads to host–guest chemistry.The ion–dipole interaction of electrostatically positive outer surface of Q[n]s with HPAs anions can well explain the formation of such water insoluble material.All these information motives us to investigate Q[n]–supported HPAs?Q[n]–HPAs?as acid catalysts for the esterification.Firstly,FTIR spectroscopy,X–ray powder diffraction,SEM and EDS,element analysis was used to analyze Q[n]–PMo₁₂?Q[n]–PW₁₂?Q[n]–SiW₁₂?n=6,8?.Resultssuggest that Q[n]–HPAs has the properties of simple preparation,porous structure and HPAs can be supported on Q[n] by the outer surface interaction of Q[n].Secondly,Q[n]–PMo₁₂?Q[n]–PW₁₂?Q[n]–SiW₁₂?n=6,8?as acid catalysts for the esterification of acetic acid with ethanol.Such supramolecular assemblies show that not only good catalytic activities in the esterification of ethanol with acetic acid,but also insoluble solid features,which can be easily isolated from reaction systems.The catalytic activities of the supported HPAs catalysts in the esterification reaction shows that firstly,the yield of esterification with Q[6]–HPAs is over 70% and the yield is around 63% with Q[8]–HPAs.Secondly,Q[n]–HPAs catalyst in the esterification reaction is easy to recycle,and has high recovery rate.The catalysts are stable and active,suggesting the Q[n]–supported HPAs hybrid materials has potential application in catalysis research with low cost.Finally,Q[5]–N₆Mo₇ trapped rare earth ions(Ln³⁺)with a preliminary analysis because Q[5] is easy to react with rare earth ions.It shows that Q[5]–N₆Mo₇ can trap rare earth ions(Ln³⁺)with a formation of Q[5]–Ln³⁺–N₆Mo₇.In the ammonia solution?pH=8¹2?,Ln³⁺ can hydrolyze and separate with Q[5]–N₆Mo₇,by which the Ln³⁺ions can recycle.