Reaçõesdeoxidaçãocatalíticas

QFL5835-6Catálise:umavisãointegradaProfs:AtaualpaBraga,LianeM.Rossi,PedroVidinha

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Selective oxidation remains one of the keysynthetic steps for the activation of a broad range ofsubstrates for the production of either finished products orintermediates for the preparation of pharmaceuticals,agrochemicals,aswellascommoditychemicals.

Epoxides,alcohols,ketones,aldehydes,

andacids

alkanesolefinsalcohols

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IncontrasttohydrogenationreactionswhichareoftencarriedcatalyticallywithH2,therearerelativelyfewselectiveoxidationreactionsthatarecatalyzedusingO2.

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WhyhydrogenationwithaheterogeneousmetalcatalystandH2isacommonplacelaboratoryprocedureandmostwouldnotconsiderdoingasimilaroxidationprocesswithO2asastandardlaboratoryprocedure?

• H2hastobeactivatedbychemisorptiononacatalystsurfacebeforeitcanbereactedwithasubstrateforhydrogenationtooccur

• O2initsgroundstateisadiradicaltripletspecies.Thisopensupthepossibilitiesofcompetingnon-catalyzedgasorliquidphasereactionsinwhichtripletdioxygenreactsdirectlywiththesubstratewithouttheinterventionofacatalyst

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• Selectiveoxidationsusingstoichiometric

oxidants:Na2Cr2O7,KMnO4,MnO2,…

• Producestoichiometricamountsofverytoxicwaste,nolongertolerable.

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• Mostindustrialoxidationprocessestendtouseeitherchlorineororganicperoxides.

• Oneproduceshugeamountsofchloridesaltsandlesser,butsignificant,amountsoftoxicchlorinatedorganicby-products.

• Thealternativeuseoforganicperoxidesisexpensive,andisalsoaccompaniedbytheformationofby-products—economicallydisadvantageousifthereisnomarketforthem.

Epoxidationwithchlorine

-Chlorine-hypochlorite-peroxyacids

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SharplessEpoxidation

•  Theoxidizingagentistert-butylhydroperoxide

Katsuki,T.;Sharpless,K.B.(1980)."Thefirstpracticalmethodforasymmetricepoxidation”J.Am.Chem.Soc.,1980,102(18),pp5974–5976

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cleanandfreelyavailablefromairO2

• CATALYTICOXIDATIONS

Thereisarealneedfornewcatalyticprocessesthatusemolecularoxygen,especiallysinceenvironmentalfactorsareofparamountimportanceandweneedtodevelopatomefficientgreenprocesses.

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Itissurprisingthattherehavebeenfewnewapproachesinthedesignofselectiveoxidationcatalystsusingmolecularoxygeninthepastfortyyears.1Themajoradvancesinselectiveoxidationweremarkedoutover50yearsago.

1G.J.Hutchings,Chem.Commun.,2008,1148–1164

• titaniumsilicaliteTS-1 àepoxidationofalkenes(H2O2)

• iron-dopedZSM-5zeolite àoxidationofbenzenetophenol(N2O)

Reaçõesdeoxidaçãocatalítica–O2

• Autoxidation mechanism

Radicalscavenger: butylatedhydroxytoluene(BHT).BHTisanantioxidantthatreactswithfreeradicals,delayingoxidativeprocesses.

Reaçõesdeoxidaçãocatalítica–O2

• Oxidation at metal or oxide surfaces

Redoxcatalysts:V,Mo,Fe•  Lowselectivity:theoxygenatedproductsaremorereactivethanthe

startingmaterials,e.g.alkanes.

-Hightemperature-Highlyactivecatalysts

• Oxidation with redox catalysts

•  Industrialapplicationofcatalyticoxidationofalkanes:

Oxidationofbutanetomaleicanhydride((VO)2P2O7-VPO))

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Fig.1.Selectivityinproductvs.D0HC–Hreactant–D0HC–HorC–Cproductat30%conversionfortheindicatedreactions[1]:1,ethylbenzenetostyrene;2,1-butenetobutadiene;3,acroleintoacrylicacid;4,toluenetobenzoicacid;5,ethanetoethylene;6,n-butanetomaleicanhydride;7,toluenetobenzaldehyde;8,propenetoacrolein;9,1-buteneto2-butanone;10,isobutanetoisobutene;11,methanoltoformaldehyde;12,methacroleintomethacrylicacid;13,propanetopropene;14,ethanoltoacetaldehyde;15,isobutenetomethacrolein;16,n-butaneto1-butene;17,benzenetomaleicanhydride;18,propanetoacrolein;19,methanetoethane;20,isobutanetomethacrylicacid;21,ethanetoacetaldehyde;22,methanetoformaldehyde;23,isobutanetomethacrolein.

Theroleofreactantandproductbondenergiesindetermininglimitationstoselectivecatalyticoxidations(AppliedCatalysisA:General137(1996)179-191)

ifthisbondenergydifference(weakestbondinreactantandproduct)islessthan30kJmol−1veryhighproductselectivityispossible,whereasfordifferencesgreaterthan70kJmol−1nearzeroselectivityisalwaysrecorded.

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COoxidationM.Haruta1wasthefirsttoshowthatCOoxidationcouldbeperformedatambienttemperaturesbyusinggolddispersedonoxidesurfaces.

1Haruta,M.;Kobayashi,T.;Sano,H.;Yamada,N.ChemLett1987,405.

TheactivegoldcatalystswerecomposedofAunanoparticleshomogeneouslydispersedonmetaloxidesupportssuchasFe2O3,Co3O4,andNiO

• Oxidation by O2 chemisorption

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COoxidation

M.Haruta,GoldBulletin2004,37/1–2,2716

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COoxidationComparison with platinum:

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COoxidationisanessentialgoalforfuelcelltechnologywhereresidualtracesofCOhavetoberemovedfromtheH2thatisusedasthefuelsource.However,thisrequirespreferentialoxidationofCOinthepresenceofCO2,H2OandamassiveexcessofH2.

COoxidation

• WhygoldissuchaneffectivecatalystfortheoxidationofCO?• WhatisthemechanismbywhichsupportedgoldnanocrystalsoxidizeCO?• Whatisthenatureoftheactivesiteandisitthesameforallsupportedgoldcatalysts?

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COoxidationProposalshaveincludedthesizeandmorphologyofthegoldparticleanditsinterfacewiththesupport,themetaloxidationstate,andsupporteffects.EXAFS,XPS,Mössbauer,IRofCOadsorbed,O2adsorptionandthereactionofO2withCO,18O2isotopeexperiments,etc.-

MetallicAusurfacesarenecessaryforCOadsorptionandthattheperipheriesactasreactionzoneswithO2

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AllattemptstoproducePOcommerciallybydirectoxidationofpropene,inasimilarwaytothesilverpromotedsynthesisofethyleneoxide,havetillnowbeenunsuccessfulandthemajorityofPOisstillmanufacturedbythechlorohydrinprocessandtheindirecthydroperoxideprocesses.

Propeneepoxidation

C.DellaPina,E.Falletta,L.PratiandM.Rossi,SelectiveoxidationusinggoldChem.Soc.Rev.,2008,37,2077–2095

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Propeneepoxidation

Hayashi,T.;Tanaka,K.;Haruta,M.JCatal1998,178,566.

Haruta,Metal.Angew.Chem.Int.Ed.2009,48,7862–7866

Propeneepoxidation“Theresultingtitaniumhydroperoxidespecies(Ti–OOH)aretheactualreactionpartnersforthepropylene,whichisconvertedtopropyleneoxide.”

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Oxidationofhigheralkenes

G.J.Hutchings,Chem.Commun.,2008,1148–1164

ComparingthecatalyticactivityofAuandPtnanoparticles

• Oxidationofn-propanal • Oxidationofaldehydes

S.Biellaetal.,J.Mol.Catal.A:Chem.(2003)197,207.

Oxidationofalcohols• Michele Rossi et al.

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Effectofsupportongoldcatalysis

A.Cormaetal.,Angew.Chem.Int.Ed.(2005)44,4066

5nmCeO2

Oxidationof3-octanol

• Avelino Corma et al.

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ComparingthecatalyticactivityofAuandPdnanoparticles

Substrate T(°C) Catalyst Ketoneyield(%) TOF(h−1)

1-Phenylethanol 160 Au/CeO2 33 12,480

Pd/CeO2 >95 32,558

120 Au/CeO2 >95 1511

Pd/CeO2 91 645

3-Octanol 120 Au/CeO2 >95 2337

Pd/CeO2 3 63

Pd/CeO2▲,Au/CeO2■ePd/apatite♦A.Abadetal.Tetrahedron(2006)62,6666.

• Avelino Corma et al.

3-Octanol

1-Phenylethanol

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• G. H. Hutchings, et al.

D.I.Enache,D.W.Knight,andG.J.Hutchings,CatalysisLetters,103,2005,43.

Oxidation of benzyl alcohol – effect of support

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• G. H. Hutchings, et al.

DanI.Enache,etal.Science311,362(2006)

ComparingthecatalyticactivityofAu,PdandAuPdnanoparticles

TiO2-supportedAu-PdalloynanocrystalsgivesignificantlyenhancedactivityforalcoholoxidationusingagreenchemistryapproachwithO2undermildsolvent-freeconditions

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(A)Au(4d)andPd(3d)spectrafora2.5weight%Au–2.5weight%Pd/TiO2catalystafterdifferentheattreatments:(a)uncalcinedor(b)calcinedat673Kinair.(B)MontageshowingtheADF-STEMimageofabimetallicparticleandthecorrespondingMSA-processedSTEM-XEDSmapsoftheAu-M2,Pd-La,O-Ka,andTi-Kasignals.AlsoshownisareconstructedMSA-filteredAu-Pd-Ticompositionmap(Ti,red;Au,blue;andPd,green).

DanI.Enache,etal.Science311,362(2006)

30 DanI.Enache,etal.Science311,362(2006)

Bimetallicnanomaterialsforthedesignofadvancedcatalysts

•  High atomic structural complexity:

•  Distribution of metal domains?

•  Composition (bulk and surface)?

•  Composition homogeneity among particles

•  Atomic rearrangement and restructuring under heating/working conditions

(a)alloy,(b)cluster-on-cluster,(c)core-shell

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Heterogeneous catalysis = surface catalysis1

Sólido

Gas Liquid

1BruceC.GatesandTobinJ.Marks,DefragmentingCatalysis(editorial),Angew.Chem.Int.Ed,2012,51,11644

1) Adsorption 2) Reaction 3) Desorption

Solidcatalyst

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Heterogeneous catalysis = surface catalysis1

Sólido

Gas Liquid

1BruceC.GatesandTobinJ.Marks,DefragmentingCatalysis(editorial),Angew.Chem.Int.Ed,2012,51,11644

Solidcatalyst

Extremelysensitivetosurfaceandsubsurfacecomposition?Howtocontrol(andknow)thesurfacecompositionofbimetalliccatalysts?

Biorefineryplatformmolecules

34JGallo,J.Braz.Chem.Soc.,Vol.28,No.9,1586-1607,2017.

H2O2

Anthraquinone process

H2 + O2

J.Am.Chem.Soc.,2016,138(2),pp574–586

DirectsynthesisofH2O2

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