Transformation of CO2 by using nanoscale metal catalysts: cases studies on the formation of formic acid and dimethylether

2018·0.52 MB·English

by  Ning Yan

Availableonline at www.sciencedirect.com
ScienceDirect
Transformation of CO by using nanoscale metal
2
catalysts: cases studies on the formation of formic acid
and dimethylether
Ning Yan1 and Karine Philippot2,3
ThevalorizationofCO hasgainedincreasinginterestinthe Ifmajorglobaleffortsmadeintheattemptstoreducethe
2
scientificandindustrialcommunitiesduringthelastdecades carbonfootprintfocusonthelong-termstorageofCO ,
2
withintensiveresearchdevotedtoCO capture,sequestration moreeffortsarerequiredinordertodeveloptechnologies
2
andutilization.Thisisbecausethegreenhousegasemission for the valorization of CO as a ‘raw material’. Indeed,
2
hasbecomeaseriousconcerntofacetheglobalclimate CO is a cheap, non-toxic, abundant, reproducible and
2
changeandthatefficientsolutionsarerequiredtoreducethe costefficientchemicalthatcanbeusedascarbonsource
carbonfootprint.UptonowthechemicaltransformationofCO forthesynthesis of fuels and various chemicalsthat are
2
intofuelsandtargetmoleculeshasbeenmainlyinvestigatedby today mainly produced from non-renewable resources
usingmolecularcatalysts.However,theabilityof [2].ConvertingCO hasthusahugeappeal,notonlydue
2
heterogeneouscatalystsornanomaterialsforthiscatalysishas tothecarbonfixationpotential,butalsobecauseitmay
beenrecentlyexploredandpromisingresultsachievedinthe complement current chemical industry by providing
productionofformicacid(FA)anddimethylether(DME)from value-added products (see Figure 1 for chemicals that
CO withnanoscalemetalcatalysts.Relevantexampleswill may be obtained from CO and their carbon capture
2 2
illustratethehighpotentialofthisclassofcatalyststhatcould capability) but today there are only nascent strategies.
offernewsolutionsfortheselectivetransformationofCO ItisnoteworthythattheproductsdescribedinFigure1
2
towardfuelsandhighaddedvaluechemicalsinthefuture. arecurrentlynot(mainly)producedfromCO dueinpart
2
to technical challenges and that major scientific break-
throughsareneededtomaketheCO routeeconomically
2
viable.Arecentreviewreportsananalysisofthestate-of-
Addresses the-art of synthetic methodologies and CO -involving
2
1DepartmentofChemical&BiomolecularEngineering,National processeswiththeassessmentoftheirlifecycleinorder
UniversityofSingapore,4EngineeringDrive4,117576,Singapore
to evaluate the potential to reduce the environmental
2CNRS,LCC(LaboratoiredeChimiedeCoordination),205routede
Narbonne,BP44099,F-31077ToulouseCedex4,France footprint relative to the current petrochemical value
3Universite´ deToulouse,UPS,INPT,F-31077ToulouseCedex4,France chain [3(cid:1)(cid:1)]. The authors tried to identify opportunities
by exploiting CO as a novel feedstock that avoids the
2
Correspondingauthors:Yan,Ning([email protected])
utilization of fossil resource in transition toward more
sustainable future production. The motivation to
CurrentOpinioninChemicalEngineering2018,20[1_TD$DIFF]:86–[2_TD$DIFF]92 develop CO2-based chemistry does not have to depend
primarilyontheamountofCO emissionsbuthastobe
ThisreviewcomesfromathemedissueonNanotechnology: 2
Nanocatalysis stimulated by the significance of the relative improve-
mentincarbonbalanceandothercriticalfactorsdefining
EditedbyHuaChunZengandHongYang
the environmental impact of chemical production in all
ForacompleteoverviewseetheIssueandtheEditorial
relevant sectors in accord with the principles of green
Availableonline26thMarch2018 chemistry.
https://doi.org/10.1016/j.coche.2018.03.006
One main issue with CO is that it displays a high
2211-3398/ã2018ElsevierLtd.Allrightsreserved. 2
thermodynamic stability [4]. CO transformation thus
2
requires developing efficient catalytic systems [5] that
offeragoodbalancebetweentheenergyneededandthe
gainobtained.Significantprogresshasbeenmadeinthe
direct electrochemical reduction of CO to fuel mole-
2
Introduction cules (like formic acid, methanol or methane) which
CO capture,storageandutilizationareafocusofinten- couldbeaviablestrategyifpoweredbyacarbon-neutral
2
sive research today, given greenhouse gas emission electricityusingnanoscalecatalysts(Pt,Co,Ni,ZnO)[6].
(where CO takes a major place) has become a serious Butonemainissuewiththisapproachistheabsenceof
2
concern in front of the global climate change [1(cid:1)], as stablecatalyststhatcanenabletheCO reductionreac-
2
illustrated by the numerous international actions from tion at low overpotential and high selectivity over the
governments, academia and industries over the past hydrogen evolution one. Photocatalytic conversion of
decades. CO based on the use of metal-doped semiconductors
2
CurrentOpinioninChemicalEngineering2018,20:86–92 www.sciencedirect.com
TransformationofCO inFAandDMEusingnanocatalystsYanandPhilippot 87
2
Figure1
HO O n
Formic acid
CxHy (fuel)
Annual Market 0.5 Mt Annual Market 2 Gt
O
H3C OH H3C CH3 M CO3
Dimethyl ether Inorganic carbonates
Methanol
Annual Marked 6.5 Mt Annual Marked 80 Mt
Annual Market 40 Mt
O
O
H N NH
R OH 2 2
Urea
Carboxylic acids
Annual Market 6.5 Mt Carbon dioxide Annual Marked 100 Mt
O O
O
O
O O R1 R
O R R NH O N
O O
n n
R R R
R O R O
H
O N
n O n n O n
(Poly)carbonates and (poly)carbamate
Annual Market >2.6 Mt
Current Opinion in Chemical Engineering
PotentialchemicalsfromCO transformation.
2
for harnessing the energy from sunlight is another With increasing worldwide interests and investments
domain of increasing interest, but improvement is still toward the valorization of CO , increased examples of
2
neededtoavoidtheuseofsacrificialelectrondonors.As producing chemicals from CO in both scientific and
2
forthechemicalreductionofCO byusinghydrogen,it industrial communities have emerged in recent years.
2
remainsasignificantchallenge. Thisprocessisthermo- A very pronounced case is the conversion of CO into
2
dynamically unfavorable, being the net reaction methanol,whichismostcommonlyproducedfromnatu-
between gaseous H and CO to liquid HCOOH ralgas.Theworld’sfirstindustrialprocessthatusesCO
2 2 2
endoergonic due to the strong entropic contribution as a feedstock for the synthesis of methanol was imple-
(DG0 ¼32:9kJmol(cid:3)1). To render the transformation mentedbyMitsuiChemicalsin2009.Thisdemonstrates
298
of CO to formic acid (or formates) feasible in practice, the feasibility of creating value from CO through the
2 2
the thermodynamic equilibrium has to be disturbed by generationofinnovativenoveltechnologiesandisanew
secondary reaction or molecular interaction. Common answertotheCO dilemma.Apartfrommethanol,formic
2
strategies are by esterification (e.g. reacting formic acid(FA;HCOOH)anddimethylether(DME;(CH ) O)
3 2
acid/formates with methanol to yield methyl formate are currently among the top in the list of chemicals that
followed by reacting with amines to yield formamides) CO can offer. Hydrogenation of CO into FA provides
2 2
orsimplyneutralizationwithabasesuchasammoniaand thesimplestandmostdirectsolutionforthelongdesired
triethylamineoralkali/alkalineearthbicarbonates.More- chemicalloopforhydrogenstorageusingCO .WhileFA
2
over, the chemical equilibrium of CO /bicarbonate is not a perfect hydrogen storage vector due to its rela-
2
(HCO (cid:3))/carbonate (CO 2(cid:3)) is influenced by many tively small hydrogen content (4.4wt%; 53gL(cid:3)1 hydro-
3 3
parameters, such as temperature, CO pressure, nature gen at room temperature and ambient pressure), it is
2
of base, and solution pH. presently still one of the best among liquid storage and
www.sciencedirect.com CurrentOpinioninChemicalEngineering2018,20:86–92
88 Nanotechnology:Nanocatalysis
transport media for H . DME is another highly interest- carbonylation of water via methyl formate or methyl
2
ingchemicalthatcanbegeneratedbydirectCO hydro- formamide. It is a two-step procedure: methanol reacts
2
genation.DMEissuperiorcomparedwithpetrodieselin withCOleadingtomethylformate(typicalconditions:a
diesel engines, since it is virtually free from sulfur and base catalyst, 80(cid:4)C, P =45bar) which is then hydro-
CO
aromatics, thus emitting less CO, SOx and particulates. lyzed in FA and methanol (autocatalyzed by FA itself)
(cid:1)(cid:1)
[3 ]. It is demonstrated that the proton transfer to the
In the past decade, relevant examples in the use of base drives the reaction. Another important issue in this
nanoscale metal catalysts for the production of FA and processistheseparationofFAfromthereactionmixture
DMEfromCO havebeenreported.Theyillustratewell that requires a dedicated extraction as well as an eco-
2
the high potential of this class of catalysts for these nomicandenergeticcost[2].Giventheabovethedirect
difficult transformations. catalyticreductionofCO offersahighlyattractiveroute
2
to get FA from an abundant raw-material by providing a
‘shortcut’tothedesiredproduct.However,thisappealing
Transformation of CO into formic acid
2 approachrequirestohaveatdisposalappropriatecatalysts
Formic acid is a valuable basic chemical, being largely
able to advantageously reduce CO to HCOOH and, if
used as a preservative, an antibacterial, an insecticide 2
targeting FA as a hydrogen carrier, catalysts able to
agentandalsoasade-icingagent.Numerousapplications
selectively decompose FA to release CO-free H .
are found in leather and tanning industries, textile and 2
rubbersmarkets,deicingofroads,silagepreservationand
DirecthydrogenationofCO intoFAwithhomogeneous
animalfeedormedicalsector,etc.FAplaysalsoamajor 2
catalysts has been extensively studied and is well-docu-
role in synthetic chemistry as an acid, a reductant and a
mentedwithseveralreviewswhereboththetremendous
precursorforsyntheses.Moreover,FAisestablishedasa
advancesinthefieldandthescientificandtechnological
liquid‘hydrogen-carrier’andthusasapromisingalterna-
challenges that remain to overcome are highlighted
tive for chemical energy storage (Figure 2) [7]. (cid:1)(cid:1)
[2,3 ,8–10]. Numerous and various active molecular
complexes in organic solvent, water, glycerol, ionic
With an annual production capacity of >300kt of FA liquids or sCO conditions at temperature in the range
compared to global 800kt, BASF is the world leader RT-120(cid:4)Carec2laimed.TheycontainmostlyRu,RhorIr
market followed by BP and Eastman. Even if it can be
butcatalyticsystemsinvolvingnon-noblemetalslikeFe,
obtained by oxidation of biomass, the most common
Co,NiandCuarealsoreported.Efficientcomplexesfor
process to produce FA relies with the formal
example display electron-rich metal centers (using elec-
tron-donating ligands) and are able to activate H under
Figure2 2
the form of hydrides and to transfer these hydrides to
CO ,forsomeofthemundermildconditions.Described
2
complexes mainly contain phosphanes which can be
H sulfonated for water solubility purpose, but carbenes or
2
pyridinederivativesareusedalso.Ligandsandthereac-
tionmediumareknowntoplayacrucialrole(forinstance
water can favor producing FA). Apart from H , other
2
Hydrogen Evolution reducing agents can be used namely, hydroboranes or
Catalyst
hydrosilanes [5,11]. The use of glycerol as hydrogen
donor has been also reported, a reaction of high interest
HHyyddrogenn
sincethisallowstoconverttwowastematerialsintouseful
CO HCOOH
2 Storaggee products [12]. In spite of the excellent catalytic perfor-
mances (both in terms of activity and selectivity)
Hydrogenation achievedbyseveralhomogeneouscatalysts,theyarestill
Catalyst farfromwhatwouldbedesiredfromanindustrialstand-
point,astheresultofthelowcatalystconcentrationsoften
(cid:1)(cid:1)
used in homogeneously catalyzed processes [13 ]. The
immobilizationofhomogeneouscatalystsatthesurfaceof
H
2 supports(mainly,silica-basedandpolymer-basedmateri-
alsorporousorganicpolymers)hasalsobeeninvestigated
because heterogenized complexes allow to circumvent
the difficulties linked to the separation and recovery of
Current Opinion in Chemical Engineering the catalyst, another issue in homogeneous catalysis
(cid:1)(cid:1) (cid:1)
[13 ,14 ]. By combining the desired properties of tun-
able,well-defined,highlyactivecatalyticsitesofahomo-
SchematicrepresentationoftheCO /HCOOHhydrogenstorage
2
system. geneoussystemwithaheterogeneousone,thisapproach
CurrentOpinioninChemicalEngineering2018,20:86–92 www.sciencedirect.com
TransformationofCO inFAandDMEusingnanocatalystsYanandPhilippot 89
2
helps with the catalyst handling and also leads to higher ong-C N thanCNT.Itisnoteworthythatthisstudyhas
3 4
activity per unit volume. beenperformedinaneco-friendlysolvent,namelywater,
withoutabaseadditiveandundermildconditions(40(cid:4)C,
Intheopposite,despitetheoldworksinvolvingPdblack 50bar H /CO =1). This result shows the strong influ-
2 2
[15]andNi-Raney[16]andtheirpracticaladvantagesfor ence of the g-C N support in comparison to CNT that
3 4
continuous operation and product separation, the devel- derives from the high CO adsorption and activation
2
opment of heterogeneous catalysts for the direct hydro- ability of g-C N which provides activated form of car-
3 4
genation of CO lags significantly behind that of homo- bonateorformatetoPdwhereH isactivated[24].This
2 2
(cid:1)(cid:1) (cid:1)
geneous catalysts [13 ,14 ]. However, the number of illustrates also well the synergetic effect between the
examples is increasing since recently in particular for metalphaseandthesupport.Thesamegroupreportedon
supported nanoparticulate metal catalysts. a PdNi catalyst supported onto a carbon nanotube-gra-
phene (CNT-GR) material where a synergetic effect is
For bulk metal catalysts, apart from the use of Pd black observedcomparedtoreferencemonometallicPdNPs,as
andRaney-Niaspreviouslycited,threepapersreporton the result of close interaction and synergy between the
the formation of FA from a mixture of H /CO gases on two metals [25]. If the catalytic performance claimed is
2 2
Au [17], Pd [18] and Ru [19] catalysts with very poor quitelower(TOF=1.2(cid:5)10(cid:3)4s(cid:3)1)thanthatofthepre-
activities.Inthelatercase,supportednanoparticleshave vious Pd/g-C N catalyst, this example highlights the
3 4
been observed but they are not well-defined. Compared interest of exploring bimetallic systems. Interestingly
tobulkmaterialswhichdisplaypooractivesurfaceandare also, a nanocatalyst constituted of very small Pd NPs
thuseconomicallyinefficientforhigh-scalecatalyticpro- (ca. 1.7nm) regularly dispersed onto a mesoporous gra-
cesses,nanoscalecatalystsarewell-knownasbeinghighly phitic carbon nitride (mpg-C N ) afforded a TOF of
3 4
dispersedmetalsthatprovidehighnumbersofactivesites 144hour(cid:3)1 under ambient and base free conditions
[20].However,despitethe hugeprogressmade in nano- [26]. This result is comparable to values reported with
chemistry and nanotechnology during the past 20 years heterogeneous catalysts in similar conditions. Another
and the fact that they were studied for the formation of relevant example about Pd is a nanocatalyst made of
FA from carbonates (mainly with Pd), only a few exam- Pd NPs (ca. 1.8nm) regularly dispersed along the fibers
ples of supported metal catalysts at the nanoscale are of a chitin material [27]. This nanocatalyst attended a
reported for the direct hydrogenation of CO , mainly TOFvalueof257hour(cid:3)1inwaterundermildconditions
2
involving Au, Pd and Ru. If in terms of catalytic perfor- (60(cid:4)C;40barH /CO =1)thusshowingthegreatbenefit
2 2
mancesthedescribedsystemsarequitefarfromthoseof brought by the chitin support. The acetamide groups in
heterogenized molecular complexes, they present inter- chitinpromotethedistributionofPdNPsonthesurface
estingbehaviorsthatremindthoseofsupportedhomoge- and accelerate the hydrogenation of CO due to its
2
neouscatalystsandthusmerittobemoreexplored.Most coordinating ability to transition metals and Lewis basic
of supports used are inorganic ones like carbon or inor- properties. Besides the good catalytic performance
ganic oxides materials, and the crucial role of metal– obtained, this work is very original as it takes advantage
support interaction in the CO hydrogenation activity ofcoordinationchemistrypropertiesofthechitinwhichis
2
is demonstrated. issued from the biomass.
So, colloidal Au nanoparticles (NPs) have been reported Surprisingly, while Ru complexes (including heteroge-
as being not active compared to supported ones and, nizedandisolatedsingle-atomicsystems[28])havebeen
among a range of supports tested, changing TiO by extensivelystudiedandareknowntobehighlyefficient
2
Al O allowed a twofold increase of the activity of Au homogeneous catalysts for FA formation, just a few
2 3
NPs(TOFof5.5hour(cid:3)1against11hour(cid:3)1,respectively), examplesofmetalsupportedcatalystswithRuareavail-
duetospecificmetal–supportinterface[21].Thisrelates able.Onecanciteacomparativestudyonthereactivityof
to the ability of the support to facilitate heterolytic H RuNPs (ca. 6.0nm) deposited onto TiO for the hydro-
2 2
dissociation.Thisprocesscanoccuronthemetalitselfor genationofCO toFA,inthepresenceornotofanionic
2
on the reactive metal–support interface. Mechanistic liquid [29]. With TOF values in the range 20–50hour(cid:3)1
studies highlighted the importance of M–H bonds obtainedatlowcatalystloadingthisstudyevidencesthe
[22,23]. A parallel can thus be made with homogeneous positive effect of the IL which acts as a solvent for the
catalysts where the hydricity properties of the metal reaction able to capture CO . Moreover, this catalytic
2
complexes are known to highly influence their catalytic systembasedonthesupportedionicliquidphaseprinci-
properties. pleshowedagoodstabilityoverrecycling.RuNPs (size
in the range 7–14nm) formed in situ in ILs are also
Similarly, Pd NPs (ca. 4.4nm) deposited onto graphitic reported as effective catalysts for the formation of FA
carbon nitride (g-C N ) were compared to CNT-sup- fromCO withhighactivity(TOFupto3300hour(cid:3)1)and
3 4 2
ported Pd NPs of similar size, leading to a catalytic aslowdecreasestabilityaftersuccessiverecycling[30].A
activity (TOF=3.1(cid:5)10(cid:3)4s(cid:3)1) that is 12 times higher very recent paper relates that CO can be selectively
2
www.sciencedirect.com CurrentOpinioninChemicalEngineering2018,20:86–92
90 Nanotechnology:Nanocatalysis
hydrogenated either to FA or to hydrocarbons by using mechanically mixed with HZSM-5. After La incorpo-
small RuFe NPs (ca. 1.8nm) in ILs under mild reaction ration,theXRDdiffractionpeaksofCuOarebroadened
conditions(DMSO/H O;60(cid:4)C;30barH /CO =2/1)and and the intensities are weakened, suggesting a decrease
2 2 2
thattheselectivitydependsonthenatureoftheanionof of the CuO particle size. The H -reducing temperature
2
the IL [31]. So, the formation of FA is favored in ILs slightly decreased for the La containing sample,
containingbasicanionswitharemarkableTOFvalueof highlighting improved reducibility of Cu. The activity
23.5hour(cid:3)1 whereas heavy hydrocarbons (up to C ) are for CO conversion increased by ca. 50% whereas selec-
21 2
more produced in the presence of nonbasic anions. The tivity toward DME was improved by 300% over the
composition of the metal alloy and the basicity/hydro- modified catalyst. Interestingly, the Cu-Fe-Ce catalysts
phobicityoftheILionpair(mainlyimposedbytheanion) werestableonstreamfor15hoursbuttheCu-Fecatalyst
appear to be the keypoints for the selective transforma- quicklydeactivatedafter6hours.Similarly,Cewasintro-
tion of CO . First, the IL forms a cage around the NPs duced into the catalyst, prepared via the homogeneous
2
that controls the diffusion/residence time of the sub- precipitation method toget Ce-Fe-Cu mixed oxide, and
strates, intermediates and products. Second, compared then mechanically mixed with HZSM-5 [34]. Again,
to Ru and Fe monometallic NPs, the presence of Fe in decrease of CuO particle size was observed. Moreover,
RuFe NPs has a dual effect: a positive metal dilution some Cu+ was identified to enter CeO lattice to form a
2
effecttowardtheformationofFAandasynergeticonefor solid solution. The enhanced dispersion ofCu is benefi-
the formation of hydrocarbons. This work clearly shows cial for CO hydrogenation.
2
that the precise design of a nanocatalyst (here a combi-
nation between metal alloy and IL support) can lead to Both CO and H have to be activated for DME forma-
2 2
chemoselectivityinCO hydrogenation.Asalastrelevant tion. Activated H (H atom on metal surface) is also
2 2
example, Ru NP prepared by reduction of RuCl in a critical to maintain the metallic state of Cu. In this
3
methyl alcohol solution under solvothermal conditions respect,addingasecondmetaltofacilitateH activation
2
showed high activity for hydrogenation of supercritical could be advantageous. A series of Pd modified Cu-Zn-
CO (sCO ) to formic acid [32]. This work which Al-Zr/HZSM-5 catalysts was prepared, which markedly
2 2
describesanothercatalystatthefrontierbetweenhomo- enhanced the DME yield and suppressed CO formation
geneous and heterogeneous systems opens the door [35]. In TPR analysis, the reducing temperature for Cu
toward the use of solution nanoparticles for the hydro- decreased sharply from ca. 200(cid:4)C to ca. 160(cid:4)C. In liter-
genation of CO . ature,itiswellestablishedthatPdOisreducedbyH at
2 2
room temperature, and subsequently dissociates H
2
In summary, to achieve an economical CO -mediated molecules. Plausibly, the chemisorb H spill over from
2
hydrogen energy cycle, the development of heteroge- Pd to adjacent Cu phase, promoting Cu reduction. The
neous catalysts for hydrogenation of CO to FA is a authors argue that the addition of Pd into Cu does not
2
challengingandhighlydesirabletask.Recenteffortshave only improve the formate hydrogenolysis step, which is
shown that the precise design of solution and supported rate-limiting, but also improves catalyst stability by pre-
nanocatalystscanleadtothechemoselectiveCO hydro- venting the oxidation of Cu by CO , enabling high
2 2
genation intoFA, makingthusaparallel with studieson activity and stability at low temperature.
molecular complexes. Prospective studies with a molec-
ularapproachcouldallowtotunemorefinelythecatalytic While HZSM-5 and Al O are the dominant solid acids
2 3
properties of nanoscale catalysts. Mechanistic details usedtosupportCu-basedNPs,efforthasbeendirectedto
beingcritical tothedevelopment ofimprovednanocata- optimizethetypeandmorphologyofzeolites.Tounder-
lysts, more efforts are also required in this direction in standtheeffectofzeolitetopologyoncatalyticproperty,
order to achieve higher performance. 2-D ferrierite (FER) and 1-D mordenite (MOR) were
synthesized and used as Cu-Zn-Zr nanoparticle carriers
Transformation of CO into dimethyl ether [36]. Both TEM and SEM images reveal that Cu-Zn-Cr
2
Transformation of CO directly into DME requires oxideNPswithsizerangingbetween30and150nmwere
2
sequential hydrogenation and dehydration reactions, well dispersed on the 2-D lamellar structure of FER. In
whichnecessitatetheparticipationofbothmetalcenters sharp contrast, the catalyst was composed of two sepa-
(oftenCu)andacidsites.ThesizeofCuparticlesplaysa ratedphases,thatis,oxideNPs(50nminsize)andzeolite
significant role in methanol synthesis activity, indirectly patches, in the case of MOR as support. As expected,
influencing DME formation. However, the control and FER supported Cu-Zn-Zr NPs exhibited significantly
maintain of Cu particle size under reactive conditions is enhanced activity in CO conversion to DME, presum-
2
non-trivial task. Recently, La was added as an active ably due to the markedly facilitated mass-transfer of
component to decrease the reduction temperature and methanol from Cu-Zn-Zr sites to zeolite surface.
the crystallite size of Cu [33]. The mixed oxide Cu-Fe
and Cu-Fe-La were prepared by homogeneous precipi- In a majority of studies, the metal and the acid catalytic
tation starting from correspondingnitrate salts, and then centers are mechanically mixed. It appears in a recent
CurrentOpinioninChemicalEngineering2018,20:86–92 www.sciencedirect.com
TransformationofCO inFAandDMEusingnanocatalystsYanandPhilippot 91
2
report that a capsule type catalyst, with Cu-Zn-Al com- Relevantexamplesalreadyhighlightthestrongpotential
positenanoparticlesasthecoreandHZSM-5astheshell, of this class of catalysts where novel solutions for the
ismoreactivecomparedwiththecatalystssynthesizedvia valorizationofCO inthefuturecouldbefoundthanksto
2
mechanical mixing [37]. Spherical carbons, prepared by more in-depth studies on better defined systems or on
hydrothermal method from glucose aqueous solution, reaction mechanism. Thus, by taking benefit of recent
were used as a template to form Cu-Zn-Al NPs. After knowledge and know-how in nanotechnology and nano-
removalofcarbonbycalcination, these NPs wereadded catalysis should lead to novel strategies in the design of
into a sol—the HZSM-5 precursor-formed from tetra- efficient and more stable nanocatalysts to achieve trans-
ethylorthosilicate,ultrapurewater,aluminumnitrateand formation of CO into FA and DME, for example by
2
sodium hydroxide. Following a hydrothermal treatment, separately optimizing the metal active sites and the
theCu-Zn-AlNPswerepackedonHZSM-5membranes. support. Strong research efforts are needed to achieve
For mechanically mixed HZSM-5 and Cu-Zn-Al parti- this goal. What is also needed is to keep in mind that
cles,CO conversionwas23%andtheyieldforDMEwas harmonization is necessary to ensure a constant and
2
merely 5% at 3.0MPa, 270(cid:4)C, whereas the capsule type dynamic balance of all things to be considered, for a
catalystreachedCO conversionof48.3%andDMEyield sustainable and green chemistry [39]. The use of H
2 2
of 23.4%, respectively. This work highlights the impor- issued from green sources like water appears as a great
tanceofengineeringtheinterfacebetweentheCu-based solution to have a closed nature’s carbon cycle.
activesitesformethanolsynthesisandthesolidacidsites
for methanol dehydration.
Acknowledgements
AnotherapproachtoengineertheCu-zeoliteinterfaceis WethanktheNationalUniversityofSingapore(NUS),theCentreNational
delaRechercheScientifique(CNRS)inFrance,theUniversite´ Paul
toaddathirdphasebetweenCuandzeolite.Inarecent Sabatier-Universite´ ofToulouse,theNationalResearchFoundation
work,SrCO wasdepositedontoCu-Zn-Alnanoparticles, (NRF2017-NRF-ANR001PRECINANOMAT)inSingaporeandl’Agence
3
before mixing with HZSM-5 [38]. The CO conversion NationaledelaRecherche(ANR;ANR-17-CE06-0017)inFrancefor
2 financialsupports.
and DME yield steadily increased when SrCO content
3
increasedfrom0%to6%,andthenstabilizedwithfurther
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(cid:1)(cid:1)ofoutstandinginterest
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