Presentation on theme: "Deposition of a soot catalyst on a metallic DPF filter, using an aqueous sol gel dipcoating technique. Els Bruneel, N. Van de Velde …S. Hoste…….., I. Van."— Presentation transcript:
1Deposition of a soot catalyst on a metallic DPF filter, using an aqueous sol gel dipcoating technique.Els Bruneel, N. Van de Velde …S. Hoste…….., I. Van DriesscheGhent University,Dep. Inorganic and Physical ChemistryKrijgslaan 281 – S3, 9000 Gent, Belgium
2Feasability study: coating of porous metallic filter: “Development of a high efficiency diesel particulate filter medium and an adequate coating technology for catalysts”Feasability study: coating of porous metallic filter:(De-NOx) soot oxidationDiesel soot filterElectric regenerationSituering: to control diesel emissions exhaust 3 technologies are important:Engine design techniquesdiesel fuel related technologies:AND: exhaust after treatmentgoal=: to develop a high efficiency diesel particulate filter medium for off road diesel vehicles.(in eerste instantie werd gekeken naar heavy duty vehicles (busses, trucks) dan naar off road diesel engines ( locomotieven, marine, tractors) en eventueel naar passager cars andd low duty commercial vehicles.Within the project Bekaert company developped an efficient filter mediumThat is resistent against thermal mechanical and chemiscal corrosion and excellent characteristics concerning efficiency.It is composed of three layers of FeCralloy short fibres, each with different fibre sizes and pore diameters. These are sintered together to obtain a filter with a variation in porosityThe top layers , or inlet, has the highest porosity and pore size , the outlet exhibits the lowest porosity and pore size.The filter exhibits a specific surface area of 4 m2/g. And a small pressure drop of 670 l/cm2.They start from short fibres , which have a curly structure. And via a mathematical simulation model a multi-stage filter is designed,Suitable for capturing soot. : the task of the filter is to phisically capture the soot particles.In the initial setup regeneration of the filter is possible with electric heating. (Daarom gebruiken ze FeCralloy, omdat dit tegen zeer hoge temperaturen bestendig is. Bij elektrisch verwarmen kunnen de piektemperaturen hoog oplopen).As the dep. Of inorganic chemistry at UGent/ Scripts is very active in the designOf new ways to deposit thin films from aqueous solutions,We were asked to deposit a catalyst on this filter.This catalyst should lower the oxidation temperature of the captured soot. Which would allow to use cheaper or better processable metal-alloys., energy can be saved. (: electric heating is no longer necessary or heating can be reduced.)Second goal: in principle :showing that it is possible to coat the filter with a thin layer of ceramic material, throughout the whole filter, without destroying the filter and without blocking the poresOpgelet: Texaco heeft expleciet gevraagd op geen enkele manier vernoemd te worden.BekaertPourous filter: three layer mediumFeCralloy: high temperature resistance
3Exhaust after treatment Ceramic based filters Wall flow monoliths Engine designFuel technologiesExhaust after treatmentCeramic based filtersWall flow monolithsCeramic fibre filtersCeramic foamsMetal based filtersSintered metal powderMetal foil based filtersMetal fibre filtersSituering: to control diesel emissions exhaust 3 technologies are important:Engine design techniquesdiesel fuel related technologies:AND: exhaust after treatmentDifferent materials have been tested so far as potential DPF materialsIn the global particulate filter market, ceramic filtes are most widely spread.But metal based filters have the benefit of strength and heat properties of metals. : low thermal stresses and good heat conductivity.And are thus resistant against thermal and mechanical shock.Among these the metal fibre filters do have a high backpressure performance and ( en plus) exhibit a higher surface area. (then the other metallic filters) Can hav a high porosity of over 95¨% are easy to make and thus are more cost effective then the sintered metal powder and the metal foil based filtersAdd some pictures..
4Coarse fitler Fine filter Loaded Soot-free “Development of a high efficiency diesel particulate filter medium and an adequate coating technology for catalysts”Coarse fitler Fine filterLoaded Soot-freeWithin the project Bekaert company developped an efficient filter mediumThat is resistent against thermal mechanical and chemiscal corrosion and excellent characteristics concerning efficiency.It is composed of three layers of FeCralloy short fibres, each with different fibre sizes and pore diameters. These are sintered together to obtain a filter with a variation in porosityThe top layers , or inlet, has the highest porosity and pore size , the outlet exhibits the lowest porosity and pore size.The filter exhibits a specific surface area of 4 m2/g. And a small pressure drop of 670 l/cm2.They start from short fibres , which have a curly structure. And via a mathematical simulation model a multi-stage filter is designed,Suitable for capturing soot. : the task of the filter is to phisically capture the soot particles.In the initial setup regeneration of the filter is possible with electric heating. (Daarom gebruiken ze FeCralloy, omdat dit tegen zeer hoge temperaturen bestendig is. Bij elektrisch verwarmen kunnen de piektemperaturen hoog oplopen).BekaertArea: 4 m2/gPress. drop: 670 l/cm2Diesel soot filterPourous filter: three layer mediumFeCralloy: high temperature resistance
5As the dep. Of inorganic chemistry at UGent/ Scripts is very active in the design Of new ways to deposit thin films from aqueous solutions,We were asked to deposit a catalyst on this filter.This catalyst should lower the oxidation temperature of the captured soot. Which would allow to use cheaper or better processable metal-alloys., energy can be saved. (: electric heating is no longer necessary or heating can be reduced.)Second goal: in principle :showing that it is possible to coat the filter with a thin layer of ceramic material, throughout the whole filter, without destroying the filter and without blocking the poresOpgelet: Texaco heeft expleciet gevraagd op geen enkele manier vernoemd te worden.
8Overview (1) Coating technique sol gel dipcoating (2) Catalyst choose catalyst/ synthesisdeposition and analysis(3) Predeposition of Buffer layerchoose buffer layer/synthesisFirst a coating technique should be selectedWe choose sol gel dipcoaten from an aqueous solution for several reasons:- it is environmentally friendly- upscaling is ‘easy’- no high vaccuum is needed- the proces of dipping in a solution is one of the only which allows to reach the inner part of the filter.in many coating techniques to deposit thin layers (CVD, sputtering), material comes from one direction,and it is very hard to avoid pore blocking- with dipcoating a high reproducibility can be obtained,- a thin layer can be deposited, so that no obstruction of the pores is generated. and: additionally: when a thin layer is deposited the chances for delamination deminish: a good adhesion is a prerequisite- Because we start from a solution, we can obtain in depth coating: not only the outer geometry of the filter is coated.Opmerking: metaal vezels gedragen zich niet hetzelfde als metaal folie. Gekende pre-treatment technieken, zoals het groeien van een ‘TGO= thermically grown oxide’ laag blijkt niet te werken op de vezels. : op de folie kun je een laag Al2O3 groeien, door de folie op te warmen, het alumina komt dan uit de folie. Bij vezels lukte dit niet.(maar het zou kunnen dat ze intussen wel gevonden hebben hoe dit haalbaar is).
9Selection, deposition and improvement Diesel soot catalystSelection, deposition and improvementStarting point: Cu and MoSelection of precursors:NaMoO4 , CuCl2 or Cu(NO)3 , KClMolar Ratio Cu/ Mo = 2/1Preparation of a Sol gel systemaddition of citric acid to form stable complexes.A catalyst was selected.We choose for a Cu and Mo containing systemWhich has shown to be an active soot catalystAnd de-NOx activity was observed.Then : select a composition and prepare a solThat allowes:- deposition of thin layer, that can be deposited without pore blocking- thermally stabel in the temperature range used- does not destroy the filterTer info: deNOx werd nooit gemeten na de veranderingen in de samenstelling, omdat de flow through reactor werd afgebroken.De katalysator in deze figuur is een Cu/Mo/KCl kat, uit een solgel proces (en met een bufferlaag van CeO2)During the test, temperature was increased. And a gas mixture of 90% Ar, 10 % O2 was preheated and flowed over the filter at a rate of 75mL/min. To illustrate deNOx properties, 100 ppm NO was added to the mixture.)
10Selection, deposition and improvement Diesel soot catalystSelection, deposition and improvementImprovement of the catalyst:better temperature stabilityremove all chloridesreduce foamingincrease activityDeposition:sol preparationchoice of complexing agentstemperature programmA catalyst was selected.We choose for a Cu and Mo containing systemWhich has shown to be an active soot catalystAnd de-NOx activity was observed.(maar wij hebben daar niet veel op gemeten, alleen bij de eerste testen, toen de reactor nog werkte)The select a composition and prepare a solThat allowed :- deposition of thin layer, that can be deposited without pore blocking- thermally stabel in the temperature range used- does not destroy the filter
11aqueous precursor-solution Diesel soot catalystPrecursor saltscitric acidpH = 7NH4OHaqueous precursor-solutiongeldrying at 60 °CCatalystThin layerthermal treatmentDip coatingGel on filterCatalystPowder
12Thermal stability, improves with addition of Ce 50/5080/20CeCuMo catalystTGA mass%100% CuMoOne of the problems with the Cu-Mo- KCl catalyst is its’ thermal stability.We could improve this, with the addition of cerium to the catalyst.Without cerium a mass los is observed starting around 550°C.Addition of cerium, (even as little as 10%) shifts this mass loss towards higher temperatures.The more Cerium added the smaller the mass loss, but the first mass % have the biggest impact.CuMoKClCe21Thermal stability, improves with addition of Ce
13Thermal Stability, TGA-MS Cu-MoCatalystTGA massm=44Cu-Mo-Ce CatalystIt is not entirely clear what is happening, butIn the mass signal from the evaporated gasses ,accompagnying the mass loss in the Cu-Mo catalyst we see a signal of mass 44, (waarschijnlijk CO2 of N2O) (superimposed on the background signal)this signal dissapears after Ce addition.Second: a mass loss starting around 800 °CAllocated to the evaporation of KCl (which is melting at 770 °C).Therefore chlorides were omitted from the catalyst.TGA massm=44
14Thermal Stability With cerium, no Cl Cu Mo KCl Ce 2 (CuCl2) 1 2 - Omitting the Chlorine from the catalyst:= no addition of KCl , and replacing CuCl2 with Cu(NO3)3Strongly improves the thermal stability.The TGA curve is now practically flat.CuMoKClCe2 (CuCl2)12-2 (Cu(NO3)2 )0.8
15Addition of Ce to a Cu-Mo catalyst Diesel soot catalystAddition of Ce to a Cu-Mo catalystThermal stability Catalytic activtiy ??So far, we have a catalystWhich has good thermal stabilityDue to addition of Cerium and ommitting the ClBUT what did this do with our Catalytic activity???
16Catalytic activity TGA/DTA roet 501 °C POWDER TGA analysis: mass loss vs temperatureDTA : exothermic oxidation reactionCoated filterFlow through reactor: temperature of soot combustion : thin film on substrate+ de-NOx testTGA/DTA10% O2 in Ar(NOx)roet501 °C5 x filter4 x 0,01 g roetThe Catalytic activity is used in two different ways.For powder samples:TGA / DTA is used in a loose contact mode to evaluate the activity of the catalyst powder.(The top of the DTA curve is choosen as a point of comparison)Influence of the composition : next slides)For coated filters, a flow through reactor was used. (more details furhter on)massaspectrometerO2 , Ar, KWS, CO2
17Catalytic activity Al2O3 CeO2 Catalyst Cu/Mo Soot Synergistic effectAl2O3CeO2Catalyst Cu/MoSootThe Influence of quantities is illustrated in this graphic representationIn the experement, we have a mixture of 2 parts of soot and 4 parts of inert Al2O3It shows that as the soot itself decomposes around °C,Replacing the inert alumina with Cu/Mo containing catalyst , results in a decrease of the combustion temperature,Then replacing more of the Al2O3 with increasing amounts of CeO2 , results in a further reduction of the combustion temperature, showing that in this setup the CeO2 is not an inert phase , but has some kind of synergsitic efect on the soot combustion.The origen of this effect is the oxygen storage capacity of CeO2:CeO2 captures oxygen (as CeO2) on moments when there is plenty of oxygen in the environment, while it gives back the oxygen as (CeO2-x) on moments there is not much oxygen in the environment . In this manner it can promote the conversion of CO into CO2.Finally, an experiment with soot and CeO2, shows that CeO2 itself is not a good catalyst.Soot combustion temp. (°C)
18Catalytic activity TGA/DTA : Fixed Ratio: Catalyst Soot Inert Al2O3 1 (Cu/Mo/Ce/Cl)SootInert Al2O3123With a fixid ratio of catalytic material towards the sootWe can evaluate how thesechanges in composition affect the combustion temperatureIn the first composition The catalyst was still containing chlorides and no CeReplacing a part of this catalyst with CeO2, (keeping the Soot / catalyst ratio fixed) a clear reduction in combustion temperature was observed.From °C towards 430 °COmitting Chlorine from this mixture did not alter the combustion temeperature.Showing that we do not need this KCl;
19Addition of Ce to a Cu-Mo catalyst Diesel soot catalystAddition of Ce to a Cu-Mo catalystThermal stability Catalytic acitivity Thin layer ??So far, we have a catalystWhich has good thermal stabilityDue to addition of Cerium and ommitting the ClThe catalytic activity has been improved,But can we now make a thin layer ???
20Deposition of the catalyst on a filter Pretraetment of the substrate was necessary in order to increase the wettibilitContact angle measurementsChemical etching+ ultrasonic treatment+ degreasingA pretraetment was necessary, to allow wetting of the FeCralloy with the aqueous solution.In these pictures we see what happens ,using a FeCralloy foil.Before treatment, a high contact angel is measuredAfter chemical etching, ultrasonic treatment and degreasing, the wetting sufficiently improvedAnd we can proceed to the actual dipping proces.Before treatment Sufficient wettingFeCralloy exhibits low wettability
21Deposition of the catalyst on a filter Dipcoatingliquidprecursor-layercleanedsubstratesolutionT>500°C, in airliquidprecursor-layerThin film
23Deposition of the catalyst on a filter Corrosion !
24Addition of Ce to a Cu-Mo catalyst Diesel soot catalystAddition of Ce to a Cu-Mo catalystThermal stability Catalytic acitivity Thin layer Corrosion protection ??So far, we have a catalystWhich has good thermal stability, catalyst is active, a thin layer is depositedBut we need to protect our substrate with a buffer layer
25Buffer layer : Introduction Choice based on :- thermal expansion coefficient- thermal stability- solubilty of precursors- temperature of synthesis- chemical properties- reaction with filter material : unknown- reaction with catalyst: positive effectCeO2Applications (other than bufferlayer for catalyst)- Buffer layer for HTS:Fuel cellsCatalystAnti-oxidant (nanoparticles)CeO2 was choosen as a bufferlayer because it has a high thermal expansion coeficient,Thus minimizing thermal stresses , (which would appear if the substrate and the buffer layer have a big difference in thermal expansion)CeO2 is thermally stabele, water soluble inorganic salts are available,CeO2 can be synthesized at moderate temperatures ( °C)As the addition of Cerium to the catalyst had a positive effect we don’t expect any negative evolution by using CeO2 as a buffer layer.CeO2 is chemically rather inert, and thus no or only moderate reaction with the FeCralloy is expected.
27Chemical composition precursor solution Buffer layer CeO2 : precursor solutionChemical composition precursor solutionConcentration of free Ce(III) and com-plexant based on :theoretic speciation calculations from complexometry as a function of pHfurther refinement through trial and errorCe:citric acid (1:1)/(1:2)/(1:3)pH = 0 – 10Ce:c.a.1:11:21:3246810pHThe same story….Search for complexing agents,Hier iets over het uitgebreidere werk van Nigel, indien niet, kan ik ook nog wel uitbreiden.In the end we choose citric acid,determined good ratios of Ce / complexant;This can be done by trial and error or based on stability constantsUitbreiding van Nigel???
28aqueous precursor-solution Buffer layer CeO2 : precursor solutionSearch for a good anti-foaming agentGlycol, butanol, octanol and silicon suspension: APTS (aminopropyltriethoxysilane)amorphous citrate gel methodCe(NO3)3citric acidadditivesaqueous precursor-solutiongeldrying at 60 °CCeO2thermal treatmentAs , again , we have to deal with the excessive foaming due to the autocombustion proces during decomposition of the Ce-citrate complex.Several anti foaming agents were evaluated.Such as Glycol, butanol, octanol, aminopropyltriethoxysilane and Basildon silicone suspension.Due to the tensio active properties of these substances, foam formation is reduced., but the quality of the bufferlayer had to be good,Sealing the substrate completely before it comes into contact with the catalyst sol.Some of them could be easily ruled out by a visual inspection, however…
29Corrosion protection: analysis Visual inspectionNot treated0,1 mm /min10 mm/minSamplescoated in Ce-nitrate/ Citric acid gel+glycol and siliconsuspension20 mm/minVisual inspection can alos be trickyOne can make a visual inspection of the coated wires,From which one can observe that, the higher the dipcoating rate, the more material is on the fibres/As seen here for samples:coated in Ce-nitrate/ Citric acid gel with the addition of glycol and siliconsuspension,After heat treatmentBut it turned out that the fast-coated samples were more sensitive corrosion then the slow coated samples !!So what happened, visual inspection clearly was not sufficientHigher dipping rate: More materialWORSE PROTECTION?
30Corrosion protection: analysis Electrochemical analysis Determination of corrosion currentAnalysis of VarianceDipping speed : 0.1 to 60 mm/minAdditivesnon10 vol% glycol10 vol% glycol 10 vol% Sil emulsionHigh temperature processSlow heating rateFast heating rateFor more profound analysis the material was analysed by linear sweep voltametry in a corrosive solution of CuCl2 (0,625 M). The corrosion current (Icorr) is taken as a point of comparison.Because of the big spread in results, analysis of variance was used to evaluate the influence of the dipcoating speed, the thermal treatment and the use of additives during synthesis, six series of samples were synthesizedCleaned filter material is coated at speeds varying from 0,1 to 60 mm/min. The used sols were a citric acid/ Ce-nitrate solution with a) no additives b) with addition of 10 vol % glycol, c) with addition of glycol and silicone emulsion.The dip-coated substrates and filters were dried at 60 °C, for 60 minutes to convert the liquid layer to a gel. Subsequently, the coated substrates were transferred to a muffle furnace and a high temperature proces was performed,Either with a fast heating rate (towards 250 °C for 60 °C and subsequently towards 800 °C for 120 minutes)Or a slow heating rate (to 250 °C with a rate of 1 °C/min, then to 400°C at 0,5°C/ min in order to cross the autocombustion regime slowly. Subsequently the temperature was kept constant at 400 °C for 1h and then raised at 1 °C/min towards 800 °C and kept constant for 2h for the crystallisation process)No statistical meaning full difference could be observed between the slow and the fast heating process.By Johan Van Brabant (Bekaert)
31Corrosion protection: analysis With higher speed, corrosion current is higher,Quality is worseCorrosion currentFrom this analysis of variance we learned that ,A smaller corrosion current is observed, when the dipcoating process was slower,Meaning that, even thought we see less material on the sample, the quality of the thin film is better, an.Dipcoating speed
32Corrosion protection: analysis Differences, concerning the additivesCorrosion currentSolCe/CACe/CA +Glycol +siliconensusp+ glycoladdition of glycol, without adding silicon emulsion is detrimental for the measured corrosion current. (P< 0,01).Regarding the use of additives, glycol has a negative effect on the porosity, consistent with what was seen in the visible corrosion inspection. From the combined use of glycol and Si-emulsion we see that this negative effect can, at least partially, be compensated by the positive effect of the Si-emulsion.
333 geometrys ‘donut’ ‘spiral’ ‘flat’ An additional problem was the geometry of the samples,The original setup of the filter is a donut like structure folded as an accordeon, but this showed to be very sensitive towards corrosion at the pleads(Top figure)Rolling the filter strip into a spiral partially solved the problem. But with time, corrosion was visibleBut in the end we had to stick to flat plates;, these are the only geometry that can be protected from corrosion over a long time (> 2 years).‘flat’
34Buffer layer CeO2 : morphology Optical microscopyElectron microscopyCe EDXOptical and EDX analysis showed that the layer of CeO2 was very thin,And that the filter was coated till the center of the filter.50 mm50 mmTop viewBack viewCut
35Deposition of the catalyst on a Buffered filter CeSEMSEM EDX of the section of the coated filterShows a nice distribution of all elements , present on the surface of the sample,Even on the inside of the filterThe micrograph shows a nice and shiny surface, evenafter prolounged time > 2 years,Showing that corrosion can be avoidedCuFeMicroscopeMo
36Diesel soot catalyst Results Cl-free Ce-containing CeO2 buffer layer: air permeability: 40%improvement required274 l/dm2.minCeO2 buffer layer:air permeability: 88 %good590 l/dm2.minConcerning the air permeability some progress is still required.
37Drop in combustion temperature Catalytic activityFilter +Drop in combustion temperature( O2 signal )No Catalyst- CCu/Mo/KCl-50 °CCu/Mo / Ce-80 °CFlow Through reactor: activity on coated filter10% O2 in Ar5 x filter4 x 0,01 g roetmassaspectrometerO2 , Ar, KWS, CO2Once coated , the catalytic activity was examined in a flow through reactor.Pieces of filter were cut into plates of 5 mm diameter.These were stacked into a reactor. In between the stacked filters 0.1 mg of soot was positioned.During the test, temperature was increased. And a gas mixture of 90% Ar, 10 % O2 was preheated and flew over the filter at a rate of 75mL/min.A reduction in combustioin temperature was registrated. In the same order of the one seen in the TGA measurements;Showing that the activity could be transferred on the filter.,And works in a flow-through set up.
39Besluit Vlakke filter kan gecoat worden na cleaning , en afzetten met bufferlaag,traag dipcoaten (1mm/min)probleem van corrosie: opgelost door :goede bufferlaagverwijderen Cl uit katprobleem thermische stabiliteit katalysatoropgelost door verwijderen Clof gebruik van hoeveelheid Ceprobleem schuim: bij bufferlaag:of Ce(NO3)3 + CA + Si-suspensieof Ce(NO3)3 + CA + Tex 1of Ce(NO3)3 + CA + APTSof Ce(NO3)3 + APTSbij katalysator:Si-suspensie indien Cl aanwezig is(?????-Cl en -Ce, APTS?????)
41Corrosion protection: analysis With a plead, the corrosion current is higherCorrosion currentIn this figure it’s shown that the corrosion current is always bigger when a plead is present in the sampleSurface area of sample (cm2)
42Composition of the catalyst Based on XRD and XPS- CuO (XRD)- NaCl (XRD)- Mo6+ (XPS)If Ce is present: CeO2 (XRD)
43Wat we weten:vereist: bufferlaagAnalyse methode voor kwaliteit van de bufferlaagmethode : elektrochemischAnalyse werking katal. : TGAAfzetten:Snelheid: trager -> hogere kwaliteit // vlugger -> meerSol: additieven van belang+ glycol: goed tegen schuim, maar mindere kwaliteit+ sil en + glycol: beter dan + glycolprobleem : batch II van siliconenen suspensie is verschillendTemperatuursproces: geen verschil tussen de 2 programma’s
44Analysis of Variance for evaluation of the use of APTS (Aminopropyltriethoxysilane)Volledig systeem
45Wat is de rol van Ce bij de thermische stabiliteit van de katalysator ? XRDHoofdzakelijk:KClCuONaClMo: ??? MoO3, MoCl5,mogelijks Molybdaten en mengmolybdatenIn Ce -oxide kat ook: CeO2XPSCu: BE typisch voor CuO, + eventueel andere faseO: in CeOxide kat: 1 piekin oxide kat en Chloride kat: 2 piekenbij hogere BE, eventueel CarbonatenCe: in Ce oxide kat: typisch mengsel van Ce III en Ce IV mengseldoor reductie van Ce IV tijdens de XPS meting.Mo: Relatief lage BE (MoCl5 of molybdaten)C: 1piek
47Pretreatment of the substrate Buffer layer CeO2 + catalyst layerPretreatment of the substrateProcessingProcessing requires good wettability.This depends on :- substrate (surface tension)- sol (surface tension, viscosity,…)cleaning involves :- degreasing- ultrasone step- etchingA. Dipcoatingliquidprecursor-layercleanedsubstratePrecursorsolutionB. Thermal treatmentT>800°C, in airliquidprecursor-layercrystalline CeO2-film