MOF+co-catalyst+allows+selectivity+of+branched+aldehydes+of+

时间:2020-02-26 21:39 来源:seo 作者:杏鑫 点击量:

MOF+co-catalyst+allows+selectivity+of+branched+aldehydes+of+

Efforts+to+develop+heterogeneous+catalysts+that+appeal+to+the+fine+chemical+industry+have+been+limited+by+underwhelming+results.+Although+some+approaches+have+shown+promising+catalytic+activity%2c+%22heterogenization%22+itself+is+not+enough.+To+be+adopted+by+industry%2c+heterogeneous+catalysts+must+promote+selectivity+that+is+difficult+or+even+impossible+to+obtain+with+existing+catalytic+systems%e2%80%94the+chemical+properties+of+any+proposed+heterogeneous+catalysts+must+go+beyond+easier+separation+and+recycling.

The+chemical+flexibility%2c+tunable+pore+size+and+chemical+and+structural+stability+of+metal-organic+frameworks+(MOFs)+make+them+ideal+for+designing+active+sites+at+the+molecular+level.+Able+to+selectively+adsorb+molecules+depending+on+their+structure%2c+they+can+direct+selectivity+and+reaction+performance.+Researchers+have+described+many+promising+catalytic+applications+using+MOFs+as+precursors+for+novel+materials+as+well+as+model+systems+for+understanding+heterogeneous+catalysis+processes.+The+field+of+catalysis+by+MOFs+is+still+in+its+infancy%2c+though%2c+since+most+examples+are+proofs+of+concept+and+do+not+offer+attractive+advantages+to+existing+catalysts.

In+a+Nature+Communications+paper+titled+%22Metal-organic+frameworks+as+kinetic+modulators+for+branched+selectivity+in+hydroformylation%2c%22+researchers+from+the+Paul+Scherrer+Institute%27s+Syncat+Group%2c+led+by+Marco+Ranocchiari%2c+and+EPFL%27s+Laboratory+of+Molecular+Simulation%2c+a+computational+group+led+by+Berend+Smit%2c+used+the+example+of+hydroformylation+to+show+that+adsorption+properties+of+MOFs+can+be+exploited+in+catalysis+to+obtain+previously+impossible+results.+The+methods+can+be+used+to+predict+the+effect+of+such+microporous+co-catalysts+in+increasing+selectivity+in+any+homogeneous+or+heterogeneous+catalytic+reaction.

Hydroformylation%2c+or+oxo+synthesis%2c+is+an+industrial+process+for+obtaining+aldehydes+from+olefins.+Current+catalytic+processes+yield+both+linear+aldehydes%2c+which+are+key+intermediates+for+the+detergent+and+polymer+industry%2c+and+branched+ones%2c+which+are+considered+a+powerful+tool+for+the+fine+chemical+industry+because+of+their+possible+use+in+producing+enantioenriched+products%2c+that+is%2c+products+featuring+a+greater+proportion+of+a+given+enantiomer+of+a+chiral+substance.

The+linear+isomers+are+often+formed+with+rhodium+catalysts.+Branched+aldehydes+are+formed+from+rhodium+catalysts+with+bidentate+ligands+with+directing+groups+to+enhance+selectivity.+Producing+the+sought-after+branched+isomers+without+these+directing+groups+is+still+a+challenge+though+and+can+only+be+achieved+through+complex+Rh+catalysts.+They+have+been+shown+to+result%2c+for+instance%2c+in+a+selectivity+for+2-methylhexanale+from+1-hexene+up+to+75%25+and+up+to+86%25+for+2-methylbutanale+from+1-butene.

The+researchers+first+screened+several+catalytic+conditions+to+maximize+the+yield+of+the+branched+product+that+could+be+obtained+with+homogeneous+catalysis.+They+then+showed+that+they+could+go+beyond+this+limit+and+achieve+much+higher+branched+selectivity+by+adding+MOFs+to+the+reaction+mixture.+They+also+tested+different+MOF+topologies+to+understand+the+role+of+the+MOF+environment+in+such+a+change+in+selectivity.

The+group+was+able+to+show+that+the+micropores+of+MOFs+push+the+cobalt-catalyzed+hydroformylation+of+olefins+to+kinetic+regimes+that+favor+high+branched+selectivity%2c+without+the+use+of+any+directing+groups.+The+addition+of+MOFs+allowed+branched+selectivity+of+up+to+90%25+in+these+cases%2c+a+feat+that+cannot+be+achieved+with+existing+catalysts.+Monte+Carlo+and+density+functional+theory+simulations+combined+with+kinetic+models+show+that+the+micropores+of+MOFs+with+certain+topologies+increase+the+density+of+the+olefins+while+partially+preventing+the+adsorption+of+the+synthesis+gas%e2%80%94this+is+what+leads+to+the+high+branched+selectivity.

Though+the+research+focused+on+aldehydes%2c+the+methods+presented+can+be+used+to+predict+the+effect+of+microporous+co-catalysts+in+increasing+selectivity+in+any+homogeneous+or+heterogeneous+catalytic+reaction.+Researchers+can+determine+the+microporous+material+that+has+the+best+chances+of+increasing+selectivity+by+first+choosing+those+that+can+adsorb+the+catalyst+while+being+inert+under+reaction+conditions%2c+and+by+then+using+simulations+to+determine+how+the+microporous+materials+might+change+the+local+concentration+of+the+selectivity+determining+reactant(s)+within+the+micropores.

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