Solid acid catalysts are widely used in the production of various high-value added and industrially important chemicals.Although the use of organosilicon compounds to modify the vacancy site has been extensively studi...Solid acid catalysts are widely used in the production of various high-value added and industrially important chemicals.Although the use of organosilicon compounds to modify the vacancy site has been extensively studied,the covalent tethering-SO_(3)H functionalized organosilicon modified polyoxometalates(POMs)has been rarely reported.In this work,two catalysts(TBA_(4)[SiW_(11)O_(39)(O(SiC_(3)H_(6)SO_(3)H)_(2))](compound 2)and TBA_(4)[SiW_(11)O_(39)(O(SiC_(8)H_(8)SO_(3)H)_(2))](compound 3))were synthesized successfully through covalently grafting different sulfonic acid(-SO_(3)H)groups onto[SiW_(11)O_(39)]^(8−)cluster,respectively.Compound 2 was achieved by surface grafting and in situ oxidation(3-mercaptopropyl)-trimethoxysilane,while compound 3 was achieved by surface grafting of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane.Strong Brønsted acid strength of compounds 2 and 3 can be demonstrated by different methods including potentiometric titration,pyridine adsorption studies,and the ^(31)P trimethylphosphine oxides(TMPO)nuclear magnetic resonance(NMR).The systematic investigation of the relationship among POM structures,acid strength,and electron density was carried out based on density functional theory(DFT)calculation and experimental results,which revealed that covalent modification of compounds 2 and 3 decreased the electron density of the O-H bond,and promoted the release of H^(+).When applied in hydroxyalkylation/alkylation(HAA)reaction of 2-methylfuran(2-MF)with cyclohexanone,compound 2 exhibited better catalytic performance with conversion of ~93%,monocyclic fuel precursors(1a)yield of 79.9% and selectivity of 85.7% than compound 3,which can be attributed to strong Brønsted acid and the intramolecular hydrogen-bonding interactions between the neighboring -SO_(3)H moieties in compound 2.Finally,compound 2 also showed excellent catalytic activity in the HAA reaction of 2-MF with several different aldehydes and ketones(e.g.,furfuraldehyde,5-methylfurfuraldehyde,acetone,butyraldehyde and 4-methoxybenzaldehyde).This result opens a new pathway for design and fabrication of novel solid acid catalysts.展开更多
Acid catalysis,one of the most important industrial processes,suffers from the toxicity,corrosion and recyclability problems of conventional homogeneous acid catalysts.Thus,the development of green heterogeneous acid ...Acid catalysis,one of the most important industrial processes,suffers from the toxicity,corrosion and recyclability problems of conventional homogeneous acid catalysts.Thus,the development of green heterogeneous acid catalysts becomes the focus of fundamental research and industrial catalysis.As a class of discrete anionic metal-oxygen clusters with tunable structure at the molecular and atomic scales,polyoxometalates(POMs)benefit from their super strong Br?nsted acidity,high proton mobility,and thermal stability.POMs-based heterogeneous catalysts have been used as the potential green alternatives to conventional homogeneous acid catalysts.In this review,we summarize recent progress on the design strategies of the POMs-based heterogeneous catalysts and their catalytic properties in acid-catalyzed reactions,where they are combined with functionalized cations,modified through covalent interactions,supported onto the non-precious metal support,and introduced into the framework of porous polymers.The design,functional strategies and catalytic performance of these POMs-based heterogeneous catalysts in specific acid-catalyzed reactions are emphasized.展开更多
基金supported by the National Key Research and Development Program of China(2017YFB0307303)the National Nature Science Foundation of China(21625101,21521005)the Fundamental Research Funds for the Central Universities(XK1802-6,XK1803-05,XK1902,12060093063)。
文摘Solid acid catalysts are widely used in the production of various high-value added and industrially important chemicals.Although the use of organosilicon compounds to modify the vacancy site has been extensively studied,the covalent tethering-SO_(3)H functionalized organosilicon modified polyoxometalates(POMs)has been rarely reported.In this work,two catalysts(TBA_(4)[SiW_(11)O_(39)(O(SiC_(3)H_(6)SO_(3)H)_(2))](compound 2)and TBA_(4)[SiW_(11)O_(39)(O(SiC_(8)H_(8)SO_(3)H)_(2))](compound 3))were synthesized successfully through covalently grafting different sulfonic acid(-SO_(3)H)groups onto[SiW_(11)O_(39)]^(8−)cluster,respectively.Compound 2 was achieved by surface grafting and in situ oxidation(3-mercaptopropyl)-trimethoxysilane,while compound 3 was achieved by surface grafting of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane.Strong Brønsted acid strength of compounds 2 and 3 can be demonstrated by different methods including potentiometric titration,pyridine adsorption studies,and the ^(31)P trimethylphosphine oxides(TMPO)nuclear magnetic resonance(NMR).The systematic investigation of the relationship among POM structures,acid strength,and electron density was carried out based on density functional theory(DFT)calculation and experimental results,which revealed that covalent modification of compounds 2 and 3 decreased the electron density of the O-H bond,and promoted the release of H^(+).When applied in hydroxyalkylation/alkylation(HAA)reaction of 2-methylfuran(2-MF)with cyclohexanone,compound 2 exhibited better catalytic performance with conversion of ~93%,monocyclic fuel precursors(1a)yield of 79.9% and selectivity of 85.7% than compound 3,which can be attributed to strong Brønsted acid and the intramolecular hydrogen-bonding interactions between the neighboring -SO_(3)H moieties in compound 2.Finally,compound 2 also showed excellent catalytic activity in the HAA reaction of 2-MF with several different aldehydes and ketones(e.g.,furfuraldehyde,5-methylfurfuraldehyde,acetone,butyraldehyde and 4-methoxybenzaldehyde).This result opens a new pathway for design and fabrication of novel solid acid catalysts.
基金supported by the National Natural Nature Science Foundation of China(U1707603,21625101,21521005,21808011,U1507102)the National Key Research and Development Program of China(2017YFB0307303)+1 种基金Beijing Natural Science Foundation(2182047,2202039)the Fundamental Research Funds for the Central Universities(XK1802-6,XK1803-05,XK1902,12060093063)。
文摘Acid catalysis,one of the most important industrial processes,suffers from the toxicity,corrosion and recyclability problems of conventional homogeneous acid catalysts.Thus,the development of green heterogeneous acid catalysts becomes the focus of fundamental research and industrial catalysis.As a class of discrete anionic metal-oxygen clusters with tunable structure at the molecular and atomic scales,polyoxometalates(POMs)benefit from their super strong Br?nsted acidity,high proton mobility,and thermal stability.POMs-based heterogeneous catalysts have been used as the potential green alternatives to conventional homogeneous acid catalysts.In this review,we summarize recent progress on the design strategies of the POMs-based heterogeneous catalysts and their catalytic properties in acid-catalyzed reactions,where they are combined with functionalized cations,modified through covalent interactions,supported onto the non-precious metal support,and introduced into the framework of porous polymers.The design,functional strategies and catalytic performance of these POMs-based heterogeneous catalysts in specific acid-catalyzed reactions are emphasized.
