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Catalysis Today 216 (2013) 185– 193

Contents lists available at ScienceDirect

Catalysis Today

jou rn al hom epage: www.elsev ier .com/ locate /ca t tod

tudy of the catalyst load for a microwave susceptible catalytic DPF

incenzo Palmaa,∗, Paolo Ciambelli a, Eugenio Melonia, Agusti Sinb

Department of Industrial Engineering, University of Salerno, Via Ponte don Melillo, 84084 Fisciano (SA), ItalyPirelli Eco Technology, Via Luraghi snc, 20020 Arese (MI), Italy

r t i c l e i n f o

rticle history:eceived 20 March 2013eceived in revised form 12 July 2013ccepted 15 July 2013vailable online 7 August 2013

a b s t r a c t

The development of a fast, safe and cost effective Diesel Particulate Filter (DPF) regeneration procedure isthe major remaining technological challenge in the use of this device. In our previous works we showedthat the simultaneous use of a MW applicator and a specifically catalyst loaded DPF, with 15%wt ofCuFe2O4, allows to reduce the temperature, the energy and the time required for the DPF regeneration.Starting by these very promising results, in this work we continued to study in order to further improve

eywords:PFootatalysisicrowave regeneration

the performances of the catalyzed DPF in terms of catalytic activity, to reduce the temperature and theMW energy required for the regeneration. The objectives of this work are to optimize the preparationprocedure of the catalytic DPF, to study the effect of the active species load, and to verify the feasibilityof the MW technology by assessing the energy balance of the regeneration phase, comparing it to theactually employed regeneration technologies. In the future we want to evaluate the activity toward theother pollutants present in the diesel exhausts (such as NOx).

. Introduction

Motivated by increasingly stringent emissions regulations,iesel Particulate Filters (DPFs) have seen widespread use as thenly technically and economically feasible means for meeting cur-ent and future Particulate Matter (PM) emissions limits [1].

Depending on the filtration mechanism, the DPF’s may be clas-ified as wall-flow and flow-through [2]. Flow-through type filters,ade of ceramic foam, wire mesh or metal wool (Fig. 1), create a

maller pressure drop which in turn benefits the fuel efficiency butt the cost of a lower filtering efficiency, often below 60% [2]. Theall-flow type filters (Fig. 2) are honeycomb monoliths made of

eramic materials such as cordierite and silicon carbide which con-ist of a series of parallel channels alternatively plugged at each endo force the exhaust gas flow through the porous filter wall [3]: theyre characterized by a filtration efficiency higher than 95% [4] ando they are the most effective system to control the soot emissionsn Diesel engines [5].

During the filtration, the porosity is progressively blocked byhe trapped soot particles, causing a growing pressure drop: sohe collected soot inside the trap has to be periodically oxidized toegenerate the DPF. The oxidation step is promoted by the so-called

passive’ (at temperatures upstream the DPF of about 200–400 ◦C)nd ‘active’ regeneration (temperatures upstream the DPF of about50–600 ◦C) [6]. The exothermic PM combustion leads in some

∗ Corresponding author. Tel.: +39 089 964147; fax: +39 089 964057.E-mail address: vpalma@unisa.it (V. Palma).

920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.cattod.2013.07.012

© 2013 Elsevier B.V. All rights reserved.

cases to excessive temperature rise, which may damage the ceramicDPF. The development of a cost effective, fast and safe regenera-tion procedure is the major remaining technological challenge inthe use of this device [7]. Recently, there has been a lot of interestin using microwave energy to accelerate chemical reactions due tothe rapid and selective heating of material through differential MWabsorption [8].

These features are also considered to be particularly suitablefor soot combustion in a SiC DPF due to the instantaneous pene-tration of microwaves into the filter body, the selective absorptionof microwaves by the soot layer [9], and the good SiC dielectricproperties, as evident from Table 1.

As indicated in Table 1, SiC seems to be the most adequate filtermaterial. In addition, from the same data of Table 1 it is evidentthat the soot is also a very good MW absorber characterized by ahigh value of the Dielectric constant ε′, and a very high Dielectricloss factor ε′′. Furthermore, formulating the soot oxidation catalystto absorb MW, the combination of MW heating with catalytic com-bustion may result in the effective oxidation of diesel soot at lowertemperature and higher reaction rate [10–12].

The results of our previous deposition and on-line regenerationtests on uncatalyzed and Copper-Ferrite loaded DPF, showed thatthe simultaneous use of the MW and the catalyst loaded filter atlower gas flow rate, allows to reduce the energy supplied and theregeneration time than that required for the uncatalyzed filter [12].

In this work we propose to optimize the preparation procedure ofthe catalytic DPF in order to maximize the load of the Copper-ferriteon the filter in agreement with a sustainable pressure drop, andto verify the feasibility of this technology by assessing the energy

186 V. Palma et al. / Catalysis Toda

Fig. 1. “Flow trough” type filter.

Table 1Dielectric properties of various materials [8].

Material Dielectric constant ε′ Dielectric loss factor ε′′

Diesel soot 10.70 3.600Quartz 3.80 0.001Cordierite 2.90 0.140

ba

2

flilg

2

smb

Alumina ceramic Al2O3 8.90 0.009Silicon carbide SiC 30.00 11.000

alance of the regeneration phase, in order to compare it to thebove described actually employed regeneration technologies.

. Materials and methods

The DPFs used in our work are Pirelli Ecotechnology SiC wall-ow monolith filters with 150 cpsi, wrapped in an heat expanding

ntumescent ceramic-mat (Interam by 3 M) and enclosed in a stain-ess steel wave guide: in Table 2 are reported the physical andeometrical characteristics of the filters.

.1. Catalyst preparation

As mentioned in the introduction paragraph, an active andtable soot oxidation catalyst if specifically formulated to absorbicrowaves may combine microwave heating with catalytic com-

ustion reaction for the effective abatement of diesel soot. It has

Fig. 2. “Wall Flow” Filter.

y 216 (2013) 185– 193

to be noted that due the microwave frequency values, on a macro-scopic scale, a good number of catalysts can be considered a goodmicrowave receptor, especially when they contains metal oxidehaving a large number of polar hydroxyl groups [10].

In the literature, the activity of catalysts based on copper andiron oxides toward soot oxidation in the presence of microwaveswas studied: in particular Ma et al. [9] performed experiments ofsoot oxidation with and without catalyst using external heatingto elucidate the influence of microwave irradiation on catalysis.They found that iron and copper were the catalysts most active inlowering the ignition temperature of diesel soot, while palladiumwas a necessary component in achieving a more complete combus-tion. In addition, the iron containing catalyst was very effective andenergy-efficient at low microwave input.

In order to optimize the performance of microwave-assisted cat-alytic combustion of soot with a catalytic filter, which is related to ahigh capability in microwave dissipation, the complex permittivityof such a material must be taken into account, as deriving from thecomplex permittivity of the all filter components, i.e. soot, catalyst,support [10]. In previous works, the regeneration of a ceramic foamfilter for soot trapping at the exhaust of a gas–oil burner had beenperformed in a specially designed single mode microwave cavity.The presence of catalyst was shown to enhance the soot oxidationrate in all the temperature ranges investigated [13,14].

The selected catalyst is based on the CuFe2O4, due to its verywell known dielectric properties and good oxidation activity [12].

3. Results and discussion

3.1. Catalyst preparation

The Copper Ferrite (CuFe2O4) is prepared starting from ironnitrate (Fe(NO3)3·9H2O), copper nitrate (Cu(NO3)2·3H2O), mixed ina 2:1 molar ratio, and distilled water, continuously stirred at 60 ◦C.The catalytic DPFs have been prepared by repeated impregnationphases in the prepared solution, drying at 60 ◦C and calcinationat 1000 ◦C after each impregnation, in order to obtain a 15%wt,20%wt, 25%wt and 30%wt load of active species. Differently fromthe previous preparation procedure [12], we lowered the dryingtemperature to 60 ◦C and changed the calcination step (abrupt heat-ing to 1000 ◦C, slow cooling to 500 ◦C and then quenching to roomtemperature): infact in the conditions previously developed andoptimized for the lower catalyst load, we observed that at highercatalyst load the pores occlusion occurs, together with the occur-rence of filter fractures which compromised its use, as also shownin literature [15]. With this new procedure, we realized a moreuniform and homogeneous distribution of the active species on theDPF walls and inside the porosity (and not only on the channelsexternal surface), reducing the occlusion of the inner walls pores,allowing to increase the catalyst load up to 30%wt.

3.2. Active species adherence testing

The adherence of the active species to the filter was evaluatedmeasuring the weight loss caused by exposing the catalyst loadedmonoliths to ultrasound, following the experimental procedurereported inn literature [16]. In this work the samples have beenimmersed in a beaker containing petroleum ether (Carlo Erba), andthe whole was placed in an ultrasonic bath CP104 (EIA SpA) filledwith distilled water, at a temperature of 25 ◦C, operating at 60% ofrated power, for 30 min. Before the test, compressed air was blown

through the monoliths in order to remove any possible residue. Theweight changes were recorded during the test at regular intervalsof 5 min after monoliths drying at 120 ◦C and cooling up to roomtemperature.

V. Palma et al. / Catalysis Today 216 (2013) 185– 193 187

Table 2Physical and geometrical characteristics of the filters.

F

0

l

W

T

ttdf

3

adpCtcTmpClSm

F

Total channels Open channels Channel length (L) (mm)

585 277 1.5

The samples weight losses were evaluated according to the fol-owing formula:

eight loss = initial weight − final weightInitial weight

× 100 (1)

he results are reported in Fig. 3.The above reported results, characterized by weight losses lower

han that reported in literature for washcoated supports [16], showhe high mechanical stability of the catalyst loaded monolith, soemonstrating the good adhesion of the catalyst on the filter sur-ace even in the absence of a washcoat.

.3. CuFe2O4 X-ray diffraction analysis

In order to verify the formation of the desired CuFe2O4, wenalyzed the powder obtained from the precursors solution afterrying at 60 ◦C and calcination at 1000 ◦C by X-ray diffraction (XRD),erformed with a microdiffractometer Rigaku D-max-RAPID, usingu-K� radiation. The results are reported in Fig. 4, where the diffrac-ion pattern of the sample obtained as previously described isompared with different samples of Cubic (database 77-0010) andetragonal (database 34-0425) Copper Ferrite and with a com-ercial Copper Ferrite (Sigma–Aldrich). XRD analysis show the

resence in the prepared Copper Ferrite of the typical peaks ofuFe2O4 in its tetragonal and cubic form with an average crystal-

ite dimensions of about 20 nm evaluated by the application of thecherrer formula; in Fig. 4 we also observe the presence of twoinor peaks correspondent to low amounts of CuO and Fe2O3.

ig. 3. Ultrasonic tests performed on 15%wt, and 30%wt catalyst loaded monoliths.

ilter wall thickness (mm) a (mm) b (mm) c (mm)

.6 36 80 124

3.4. SEM-EDAX results

Catalyzed and uncatalyzed samples have been investigated byScanning Electron Microscopy (SEM), using a Scanning ElectronMicroscope (SEM mod. LEO 420 V2.04, ASSING), and Energy Disper-sive X-ray Spectroscopy (EDX), performed in an Energy DispersiveX-Ray analyzer (EDX mod. INCA Energy 350, Oxford Instruments,Witney, UK): the results are shown in Figs. 5 and 6.

The comparison between a frontal channel of an uncatalyzedfilter and a 30%wt of Copper Ferrite loaded DPF (Fig. 5), shows thevery homogeneous distribution of the active species on the filtersurface. In Fig. 6 is shown the comparison among the channel wallsof the uncatalyzed filter and the catalyst loaded filter with 15%,20%, 25% and 30%wt of Copper Ferrite: besides the homogenousdistribution of the active species, is clear that their increasing loadresults in the decrease of the pore diameter We can also see that theactive species cover all the SiC granules surface and that increas-ing their load, they deposit on another layer of Copper Ferrite. InFigs. 7 and 8 are reported the SEM images and the elements dis-tribution as obtained by EDX element mapping, for the uncatalyticand for the 15%wt of active species loaded filter, respectively.

Figs. 7 and 8 reveal that while on the uncatalytic filter theencountered elements are only C, O and Si (the structural elementsof the filter), on the catalytic filter the encountered elements arealso Cu and Fe, the catalyst active species: these results confirmthat with our catalytic filter preparation procedure, we can obtainthe deposition of the active species on the support without anywashcoat.

3.5. Hg porosimetry tests

In order to evaluate the decrease in the median pore diameter,revealed by the SEM images in Fig. 6, the porosimetric charac-teristics of the filters have been measured by the Hg penetrationtechnique using the “PASCAL 140” and “PASCAL 240” Thermo

Fig. 4. comparison of CuFe2O4 XRD spectra.

188 V. Palma et al. / Catalysis Today 216 (2013) 185– 193

cataly

Fm

itttToas

Fig. 5. Frontal channels SEM images of an un

innigan instruments: the results are reported in Fig. 9 and sum-arized in Table 3.From the data above showed, it is evident that the increase

n the CuFe2O4 load results in the median pores diameter andotal pore volume decrease. In particular, the main changes ofhese values are observed up to 20%wt of active species, whilehe further increase from 20% to 30%wt gives only little decreases.

hese results indicate that the highest pore diameter reductionccurs at the lower catalyst load, while for the two highest cat-lyst loads the reduction in the pores diameter seems to be verymall.

Fig. 6. SEM images of the uncatalyzed (a) and the catalyzed

zed and a 30%wt of CuFe2O4 catalyzed DPF.

3.6. TG-DTA analysis

The catalytic activity of powder catalyst and catalyzed DPF, wasevaluated by simultaneous TG-DTA analysis (SDT Q600 TA Instru-ments) of soot alone and of soot mixed in a mortar with milledcatalyst loaded DPF samples at different catalyst load (15, 20, 25and 30%wt of Copper Ferrite) and with the powder catalyst. Sam-

ples were heated in air (flow rate = 100 Ncm3 min−1) from 293 to973 K with a heating rate of 10 K min−1. The results are reported inFig. 10, as derivative weight (in %/min), referred to the total amountof soot in the sample, as function of Temperature. The TG curve

DPF with 15% (b), 20% (c) and 30%wt (d) of CuFe2O4.

V. Palma et al. / Catalysis Today 216 (2013) 185– 193 189

taine

ot6

pt4tCiaai

TP

Fig. 7. SEM image and distribution of elements, as ob

f soot alone shows the typical behavior of this material (ignitionemperature of about 550 ◦C and maximum reaction rate at about20 ◦C).

The results relevant to the TG of soot mixed with the CuFe2O4owder show that the ignition temperature is lowered to 380 ◦C andhe maximum combustion rate temperature is lowered to about50 ◦C, confirming its very good activity toward the soot oxida-ion. The comparison of the results relevant to the soot mixed withuFe2O4 catalyzed DPF at different catalyst load, show that increas-

ng the load of active species on the filter the ignition temperaturend the maximum combustion rate temperature are both lowered

nd, more important, the rate of the catalytic combustion reactionncreases.

able 3orosimetric characteristics of the catalyzed and uncatalyzed filters.

Medium porediameter (�m)

Total porevolume(mm3/g)

Uncatalytic SiC DPF 17.0 329Catalytic DPF with 15%wt of CuFe2O4 14.7 264Catalytic DPF with 20%wt of CuFe2O4 13.3 247Catalytic DPF with 25%wt of CuFe2O4 12.3 143Catalytic DPF with 30%wt of CuFe2O4 12.0 134

d by EDX element mapping, for the uncatalytic filter.

3.7. H2-TPR analysis

The H2-TPR measurements were carried out using a SiC mono-lith loaded with 15%wt of CuFe2O4 from room temperature to900 ◦C at a heating rate of 5 ◦C/min in 5% H2/N2 flow. The reac-tion parameters (temperature and concentrations) have beenmonitored by the mean of an HIDEN Analytical system, able to dis-continuously sample up to 20 gas streams, subsequently sent to amass spectrometer.

Fig. 11 shows the H2-TPR profile: two pronounced reductionpeaks were observed at about 300 ◦C and 610 ◦C; these peaks areattributed to the reduction of CuFe2O4 to Cu and Fe3O4, and subse-quently of Fe3O4 to Fe [17]. The two reactions are

3CuFe2O4 + 4H2 → 3Cu + 2Fe3O4 + 4H2O (2)

Fe3O4 + 4H2 → 3Fe + 4H2O (3)

The total amount of H2 consumed for Cu mole (H2/Cu ratio) was 4.4,which is consistent with that for the complete reduction of CuFe2O4to Cu and Fe according to the following reaction:

CuFe O + 4H → Cu + 2Fe + 4H O (4)

2 4 2 2

The value of 4.4 above reported corresponds to about 17%wt ofCuFe2O4, that is in a quite good agreement with the estimated15%wt of CuFe2O4 on the monolith.

190 V. Palma et al. / Catalysis Today 216 (2013) 185– 193

by ED

mhtlo

3

pa

rogp

TB

Fig. 8. SEM image and distribution of elements, as obtained

Furthermore, as shown in literature [18], after the reduction,ixture of Cu and Fe is favorable for the formation of CuFe2O4 at

igh temperature (about 800 ◦C in air). The TPR profile showed thathe catalyst loaded monolith is able to act as a redox oxidation cata-yst active in the temperature range 300–800 ◦C due to the presencef a very good and homogeneous Copper Ferrite dispersion.

.8. Bending strength tests

In Table 4 are shown the results of the bending strength testserformed in the Pirelli Ecotechnology laboratory on the catalyzednd uncatalyzed SiC samples.

As evident from these data, the increase in the catalyst load

esults in a higher DPF bending strength, even if the main gain isbserved up to 15%wt of CuFe2O4, while the further increase to 30%ives an almost unappreciable rise. These results are in line with theorosimetric results, indicating that at the lower catalyst loads the

able 4ending strength of catalyzed and uncatalyzed SiC samples.

Wall thickness(mm)

Uncatalytic SiC DPF 0.58

15%wt of CuFe2O4 Catalytic DPF 0.58

30%wt of CuFe2O4 Catalytic DPF 0.55

X element mapping, for the 15%wt CuFe2O4 catalyzed filter.

active species deposition occurs simultaneously inside the poresand on the walls of the DPF, while at the higher catalyst loads theCopper Ferrite seems to mainly deposit on the external surface.

3.9. Catalytic activity tests

3.9.1. Diesel soot filtration efficiencyOne of the main characteristics of a DPF system is its filtration

efficiency. Known the soot concentration in the exhaust streambefore and after the filter, is possible to obtain the filtration effi-ciency using the following equation:

�f = Cbefore − Cafter × 100 (5)

Cbefore

with Cbefore is the soot concentration in the exhaust stream beforethe filter; Cafter is the soot concentration in the exhaust stream afterthe filter.

Channel (mm) Bendingstrength (MPa)

1.56 301.53 501.56 52

V. Palma et al. / Catalysis Today 216 (2013) 185– 193 191

Fig. 9. Pore size distribution at various catalyst loads.

Fig. 10. TG test performed on soot alone, soot and CuFe2O4, soot and SiC WFF with15%wt, 20%wt, 25%wt and 30%wt of CuFe2O4.

Fig. 11. H2-TPR profile of a SiC monolith catalyzed with 15%wt of CuFe2O4.

Fig. 12. DP profile during a soot deposition test on a catalytic DPF.

All the soot concentrations are obtained correlating the opac-ity and the soot load in the exhaust stream at different operatingconditions of the diesel engine in terms of rpm and oil pressure.

In Table 5 the filtration efficiency of the Pirelli SiC WFF arereported for different engine operative conditions:

Results of Table 5 shows that the filter filtration efficiency isalways higher than 99% in all the different engine operating con-ditions, so confirming the efficiency and effectiveness of thesesystems as soot filters.

3.9.2. Deposition and on-line MW assisted regeneration testsSome deposition and MW assisted regeneration tests have been

performed on catalytic DPFs with different CuFe2O4 loads, applieddirectly at the exhaust of a little bi-cylindrical diesel engine avail-able in our laboratory plant. The typical behavior of the pressuredrop through the filter (DP) during the deposition phase at the oper-ating engine conditions of 1500 rpm and Poil = 30 bar, with a fixedflow rate into the filter of about 100 l/min, is reported in Fig. 12.

The data show the stages involved in the soot loading in the DPF:depth filtration, in which soot disperse deep inside the filter-wallpores and form pore bridges thus causing a significant decreasein filter wall porosity and a further increase in the pressure dropvalues, and cake filtration, in which the soot layer reaches an appre-ciable thickness on the DPF surface, and starts to act itself as a filter.When the valued soot load is about 5 g/l, we started the MW assistedregeneration phase.

In Fig. 13 are reported the pressure drop through the filter (DP)and the outlet gas temperature as function of time during the regen-eration phase of two catalytic DPFs, with 15% and 20%wt load ofactive species. In all the tests, as showed in our previous works[12], we heat the DPF with a lower gas flow rate (30 l/min), withthe MW generator set at 50% of its maximum power. In all the tests

the DPF average filtration efficiency is about 99.5%.

As evident from Fig. 13, simultaneously to the MW application,the outlet gas temperature and the slope of DP-time curve both

Table 5Pirelli SiC WFF filtration efficiency.

Rpm Opacityin (%) Cin (mg/m3) Opacityout (%) Cafter (mg/m3) Eff (%)

600 58.9 143.1 0.3 0.5 99.71100 24.9 58.2 0.2 0.4 99.41500 29.5 69.3 0.1 0.1 99.81900 13.8 31.2 0.1 0.2 99.7

192 V. Palma et al. / Catalysis Today 216 (2013) 185– 193

Table 6Comparison of the energy required in DPF regeneration.

Regeneration technology Regeneration energy required (kJ)/DPF liters

MW assisted regeneration of 15% CuFe2O4 catalyzed SiC DPF 5700MW assisted regeneration of 20% CuFe2O4 catalyzed SiC DPF 3300Fuel post-injections [19]

iwvsT(2cdnt

etihTDn(5t7tpsr

t

ihic

[

[

[1001–1006.

Fig. 13. DP and temperature profiles during the regeneration phase.

ncrease; by looking more deeply, it is possible to emphasize thathen the temperature reaches the catalyst threshold temperature

alue, the DP curves show a plateau indicating that the catalyticoot combustion rate is comparable to the soot deposition rate.he increase in the catalyst load results in a decrease of this value350 ◦C vs 400 ◦C) and in a faster regeneration phase (25 min vs0 min). Besides it is important to note that, as consequence of theatalyst load increase from 15%wt to 20%wt, also the initial pressurerops across the filter increase, growing from 30 to 50 mbar (hereot reported, while in Fig. 13 we reported only the data relevant tohe regeneration phase).

The comparison of the MW energy supplied during the regen-ration of the two different DPFs (about 2000 kJ and 1185 kJ forhe 15% and 20%wt CuFe2O4 catalyst loaded filters, respectively),ndicates that the increase of the active species load results in aigher catalytic activity and a further lower energy consumption.he comparison of the energy required in MW assisted catalyticPF regeneration and in the actually employed regeneration tech-ologies, summarized in Table 6 as Regeneration Energy requiredkJ) for DPF liters, performed with a soot load on the filter of about

g/l, shows that the simultaneous use of the MW technology andhe 20% CuFe2O4 catalyzed DPF allows an energy saving of about7% with respect to the traditional fuel post-injection regenerationechnology [19], performed adding the fuel added via in-cylinderost-injection event to heat exhaust (DOC exotherm) and held untiloot oxidation is complete (typically about 430 g of extra fuel areequired in a 1.9 l 4 cylinder diesel engine).

The data above reported confirm the palatability of the MWechnology in the DPF regeneration phase.

Anyway, it is important to note that the optimal catalyst loads represented by the maximum load at which the activity is the

ighest, with a simultaneous still acceptable pressure drop value,

n order to avoid too high pressure drops across the DPF and aonsequently abnormal engine’s operation.

[

[

14,640

4. Conclusions

The objectives of our work were to optimize the preparationprocedure of the catalytic DPF and the load of the active species onthe filter, and to verify the feasibility of this technology by assessingthe energy balance of the entire process, in order to compare it tothe above described actually employed regeneration technologies.The new preparation procedure (drying step at a lower tempera-ture, 60 ◦C instead of 120 ◦C, and for a longer time, and differentcalcination step) assures a more homogeneous distribution of theactive species on the DPF. The XRD analysis of the prepared CuFe2O4confirmed the presence of the characteristic peaks of the CopperFerrite in its tetragonal and cubic form, so indicating that with ourpreparation procedure we can obtain the desired catalyst. The anal-ysis performed on the DPFs showed that the increase in the load ofactive species up to 30%wt resulted in:

- lower soot oxidation temperature and increased reaction rate;- decrease of the median pore diameter and total pore volume;- higher bending strength.

The deposition and on-line regeneration tests performed usinga catalytic DPF with 15% and 20%wt catalyst load showed thatthe increase in the active species load resulted in higher initialpressure drops across the filter, in a lower maximum combustiontemperature and in a faster regeneration phase, so confirming theTG-DTA results, and, more important, in a further lower energy con-sumption. The comparison of the energy required in MW assistedcatalytic DPF regeneration and in the actually employed regener-ation technologies, shows that the simultaneous use of the MWtechnology and the CuFe2O4 catalyzed DPF allows an energy sav-ing of about 77% with respect to the traditional fuel post-injectionsregeneration technology.

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