Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH 3-SCR

FeVO4 and Fe0.5Er0.5VO4 were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO2-WO3-SiO2 (TWS) and redox active supports like CeO2 and CeZrO2 with the aim of finding a suitable formulation for simultaneous soot abatement and NH3-SCR and to understand the level of interaction between the two reactions. A suitable bi-functional material was identified in the composition FeVO4/CeZrO2 where an SCR active component is added over a redox active support, to increase carbon oxidation properties. The influence of the presence of ammonia in soot oxidation and the effect of the presence of soot on SCR reaction have been addressed. It is found that the addition of NO and NO/NH3 mixtures decreases at different levels the oxidation temperature of carbon soot, while the presence of carbon adversely affects the NH3-SCR reaction by increasing the oxidation of NH3 to NO, thus lowering the NO removal efficiency.


Introduction
The study of Diesel exhaust after-treatment technologies is focusing on one side in finding novel formulations for active soot oxidation [1] and de-NO x catalysts [2][3][4] and on the other side in looking for suitable strategies to limit the number of different process units and combine more functionalities in one single step [5].Nowadays, the mobile exhaust gas after-treatment is comprised of a series of stand-alone devices, starting from an oxidation catalyst (DOC), a diesel particulate filter (DPF) and a de-NO x reactor which includes a NO x storage/reduction system or, alternatively, a NH 3 -SCR (Selective Catalytic Reduction) unit.Among the NO x removal technologies, Selective Catalytic Reduction with NH 3 (NH 3 -SCR) has been successfully employed both in stationary and heavy duty mobile applications [6].
Increasingly restrictive limitations concerning emissions of nitrogen oxides and soot particulates from vehicle engines will demand the simultaneous application of a particulate filter and a SCR de-NO x system.The motivation for the integration of the two reactions is to obtain a reduction of cost and volume of the engine after-treatment system via inclusion of SCR and DPF functionalities into a single entity.Different bi-functional configurations are possible with DPF and SCR catalyst placed in the same housing [7], or with a DPF filter coated with an SCR catalyst formulation [8][9][10].
The aim of this work is to study the behaviour of a suitable catalyst with acceptable performances both in soot oxidation and in the NH 3 -SCR reaction conducted simultaneously.For this purpose, an active SCR catalyst formulation has been loaded over supports showing different soot oxidation functionalities.SCR catalyst materials were selected among metal/rare earth vanadates that have been shown to act as efficient catalyst precursors for NH 3 -SCR reaction [11][12][13][14][15][16], while among the different supports, standard TiO 2 -WO 3 -SiO 2 (TWS) was used and compared with more efficient carbon oxidation carriers like CeO 2 and Ce 0.75 Zr 0.25 O 2 [17].In particular, this work investigates FeVO 4 and Fe 0.5 Er 0.5 VO 4 supported on TWS, CeO 2 , Ce 0.75 Zr 0.25 O 2 (CeZrO 2 ), and Al 2 O 3 in the simultaneous soot oxidation and NH 3 -SCR reactions.Specific attention is given to the influence of all the components of the complex atmosphere under which these catalysts operate and to the study of the interactions between the two reactions.A promising catalytic system is proposed as a suitable candidate for both reactions.

Catalysts Characterization
All the samples were characterized by B.E.T. (Brunauer-Emmett-Teller) surface area measurements (reported in Table 1 and Table S1) and powder XRD analysis.As it can be observed, the specific surface area of bare supports is negatively affected by the loading of iron vanadate (B.E.T. = 4 m 2 /g) and iron erbium vanadate (13 m 2 /g).XRD patterns of samples made with FeVO 4 are reported in Figure 1A, whereas XRD diffraction patterns of supported Fe 0.5 Er 0.5 VO 4 are reported in Figure 1B.In the diffraction profile of 8.4 wt % FeVO 4 /TWS only diffraction lines due to anatase-TiO 2 and Fe 2 O 3 were observed.This is due to partial decomposition of FeVO 4 on TiO 2 -based supports following thermal treatments [14,18].This decomposition generates Fe 2 O 3 plus VO x species which at low coverage are not detected by XRD, while the remaining FeVO 4 could not be clearly identified because of superposition of its main diffraction line to the anatase main diffraction peak.In the XRD pattern of 8.4 wt % FeVO 4 /CeO 2 instead, diffraction lines due to CeO 2 , Fe 2 O 3 , and CeVO 4 are identified.In this case, the precursor FeVO 4 partially decomposes releasing Fe 2 O 3 and VO x species, which then react with CeO 2 already at 650 • C, resulting in the formation of CeVO 4 [19].A very similar situation was detected for the 8.4 wt % FeVO 4 /Ce 0.75 Zr 0.25 O 2 catalyst.The formation of surface VO x species was confirmed by Raman spectroscopy on a representative 8.4 wt % FeVO 4 /TWS sample calcined at 650 • C (Figure 2).We observed Raman shifts at ca. 1000 cm −1 that have been attributed to monomeric or dimeric species formed upon decomposition of FeVO 4 [20][21][22].By carefully looking at different spots of the sample, also on the remaining FeVO 4 , that were not observed by XRD, was easily detected by Raman as highlighted in Figure 2. FeVO 4 decomposition takes place also on alumina as revealed by Fe 2 O 3 peaks in 8.4 wt % FeVO 4 /Al 2 O 3 diffraction pattern.Also in this case this is accompanied by the release of non-detectable VO x species.Residual FeVO 4 species, not detectable by XRD, could be identified by Raman spectroscopy also on 8.4 wt % FeVO 4 /Al 2 O 3 , as shown in Figure S1.
XRD spectra of supported Fe 0.5 Er 0.5 VO 4 (Figure 1B) are characterized by the presence of ErVO 4 and Fe 2 O 3 .It was previously highlighted that Fe 0.5 Er 0.5 VO 4 does not form a solid solution and the two vanadates (FeVO 4 and ErVO 4 ) are present as an intimate physical mixture [13].The FeVO 4 fraction of the mixed vanadate partially decomposes releasing Fe 2 O 3 and VO x , while ErVO 4 , which is more thermally stable than FeVO 4 [23], can still be detected on the various supports.
For a better understanding of the effect of the vanadate-support interaction on catalytic activity, some additional investigations were conducted also on a family of catalysts made by loading 50 wt % of vanadate on the support.Their XRD diffraction profiles are reported in Figure S2 of the supplementary material; as already noticed for 8.4 wt % FeVO 4 loading, the presence of Fe 2 O 3 in the XRD patterns and of VO x in Raman spectrum (Figure S3) indicates that part of FeVO 4 is decomposed.Catalyst reducibility was measured by temperature-programmed reduction under H 2 atmosphere (TPR).Since many reducible species are involved, complex reduction profiles were obtained, as shown in Figure 3. From XRD results it is clear that FeVO 4 undergoes decomposition over all supports, with the formation of surface Fe 2 O 3 , VO x and, on ceria-containing supports, CeVO 4 .On Al 2 O 3 , which is a non-reducible support, all contributions to reduction profile are related to Fe 2 O 3 , VO x , and FeVO 4 species.The attribution of the single TPR peaks is not straightforward, but similarly to what reported for FeVO 4 supported on TWS [24], the low temperature feature can be related mostly to the reduction of Fe 2 O 3 and VO x species, whereas at increasing temperature H 2 consumption due to FeVO 4 reduction is detected.At higher loading, an increase in hydrogen consumption is observed, which has been tentatively attributed to the residual part of FeVO 4 , based on quantitative analysis obtained also from XRD spectra.The onset reduction temperature is independent from FeVO 4 initial loading (Table 1).TWS reduction profile (Figure 3A) is characterized by three reduction steps of WO 3 with the main hydrogen consumption taking place in the 800-950 • C range [25].This feature is maintained also in the supported catalyst.Hydrogen consumption at lower temperature for 8.4 wt % FeVO 4 /TWS (400-700 • C) is due to reduction of the supported species VO x , Fe 2 O 3 , and FeVO 4 .As for Al 2 O 3 samples, it is noteworthy that the onset temperature of reduction is not related to the vanadate loading (Table 1).TPR profile of CeO 2 shows a low-T reduction feature due to surface species and a higher-T peak due to bulk reduction, as expected for pure ceria [26].For Ce 0.75 Zr 0.25 O 2 one single hydrogen consumption peak is detected in the medium temperature range, in agreement with reported TPR profiles of ceria-zirconia solid solutions [27].In the case of CeO 2 -containing supports, a difference in the onset of the reduction can be detected at increasing FeVO 4 loading, in contrast to what observed for TWS and Al 2 O 3 -supported vanadates, indicating a strong influence of vanadate loading on sample reducibility.The temperatures of the onset of reduction are reported in Table 1 together with the overall hydrogen consumption and the H/V atomic ratio.As it can be observed from Table 1 and Figure 3, when increasing the vanadate loading up to 50 wt % the reduction peaks become more intense, the overall H 2 consumption increases but with a lower H/V ratio, indicating a better reducibility of the low-loaded samples.

Soot Oxidation Activity
Table 2 shows soot oxidation efficiency of the samples investigated under air atmosphere.For 8.4 wt % loaded catalysts activity under NO/N 2 /O 2 and NO/N 2 /O 2 /NH 3 mixtures is also reported.
Soot oxidation values (T50) of the vanadates supported on TWS indicate the low efficiency of TiO 2 -based materials in this reaction, as reported in the literature [17].Compared to the oxidation potential of pure vanadates (FeVO 4 and Fe 0.5 Er 0.5 VO 4 ) supported catalysts show an increase of T50.These formulations were compared with those obtained by loading vanadates on supports that are known to be more active for soot oxidation like CeO 2 and Ce 0.75 Zr 0.25 O 2 [28].
As expected, CeO 2 -based materials show lower values of T50.This can be explained through the so called "active oxygen mechanism" where, thanks to the redox ability of ceria, oxygen can be activated over a vacancy and spill over the carbon soot for oxidation [17,29,30].Conversely, the use of redox inactive supports like Al 2 O 3 , results in catalyst with the highest T50.A comparison of the TPR profiles reported in Figure 3 with the corresponding onset temperatures of reduction (Table 1) evidences the correlation between sample reducibility and soot oxidation behavior.Bare CeO 2 or Ce 0.75 Zr 0.25 O 2 are the most active materials thanks to their low-temperature surface reducibility.Even with 8.4 wt % FeVO 4 a change in the onset temperature of reducibility of ceria is observed and, consequently, soot oxidation activity is lowered.For 50 wt % FeVO 4 /CeO 2 , the reduction is further shifted towards higher temperatures resulting in a higher soot oxidation temperature (Table 2).The opposite is obtained for TWS materials, for which an increase in FeVO 4 loading favours activity as no detrimental effect is displayed on reducibility in the temperature range of soot oxidation.These results clearly show that the mechanisms involved in soot oxidation on ceria and ceria-zirconia are different than those observed over TWS and alumina.This is better understood by looking at Figure 4 which shows the correlation between soot oxidation activity of pure and supported vanadates against loading.Similar results were obtained with FeErVO 4 (Supplementary material Figure S4).For FeVO 4 supported on either Al 2 O 3 or TWS the addition of FeVO 4 progressively increases activity.The effect is much more pronounced on TWS, where a strong influence is already observed at low loading.On Al 2 O 3 , a simple dilution effect seems to prevail, with a linear decrease in T50 going towards pure FeVO 4 .From XRD analyses of these compounds (Figure 1 and Figure S2) it can be observed that both in Al 2 O 3 and TWS samples the decomposition of FeVO 4 is confirmed by the presence of Fe 2 O 3 diffraction lines (corresponding VO x were detected by Raman spectroscopy on TWS support-Figure 2 and Figure S3 in supplementary material).If on TWS the role of VO x formed is essential for soot oxidation enhancement, FeVO 4 decomposition on Al 2 O 3 does not have the same beneficial effect and activity is governed simply by the dilution of the catalysts components.An opposite trend is observed with CeO 2 and Ce 0.75 Zr 0.25 O 2 -based materials, where the highest activity is obtained with the two bare supports; the activity then decreases reaching a minimum for the 50 wt % mixtures to increase again in correspondence of the pure vanadates.This catalytic behaviour is due to formation of CeVO 4 which is less active than either CeO 2 or FeVO 4 (Table 2).For the catalyst with a higher vanadate loading, the higher amount of CeVO 4 formed (Figure S2A in supplementary material), contributes to a further decrease in activity.
The effect of addition of NO and NO/NH 3 to the gas feed stream for soot oxidation was also evaluated (Table 2).In comparison to O 2 /N 2 atmosphere, the presence of NO enhances soot oxidation performances of the catalysts by lowering the peak temperature due to the formation of NO 2 with its better oxidation properties compared to O 2 [31].In a subsequent step, 500 ppm of ammonia were added to the feed gas mixture with the overall effect of slightly lowering Tp temperature for almost all catalysts (Table 2).The positive effect of the presence of NH 3 on soot combustion efficiency using NO 2 was observed by Tronconi et al. for Cu-Zeolite catalysts [32].

NH 3 -SCR Activity
NO conversion (defined as {[NO in ] − [NO out ]/[NO in ]}) in the NH 3 -SCR reaction was investigated for the vanadates on the different supports.Figure 5 compares their activity in the range of temperature 200-500 • C. The NO reduction profile shows a typical volcano-type shape with NO conversion increasing with temperature up to a maximum value which is reached at ca. 300-450 • C depending on the catalyst composition.At this point, the activity starts to decrease due to the ammonia oxidation reaction which is prevailing over NO reduction to N 2 .The activity of supported FeVO 4 is higher than that of Fe 0.5 Er 0.5 VO 4 irrespective of the support used, in agreement with our earlier findings [13].Among the different carriers, the highest activity is found with TWS, for which maximum conversions in the range 80-100% are reported.The best performing de-soot catalysts show lower activity in the standard NH 3 -SCR reaction with NO conversion values in the range 45-60% at medium SCR temperatures.Al 2 O 3 -based catalysts are almost inactive up to 250 • C. Overall, the NO x conversion values coupled with the better efficiency in carbon soot oxidation at lower temperature makes vanadates supported on CeO 2 and Ce 0.75 Zr 0.25 O 2 as promising catalysts to investigate the interaction between the two reactions occurring simultaneously.

Simultaneous NH 3 -SCR and Soot Oxidation Activity
To study the influence of soot oxidation on SCR reaction, a different set up configuration was used employing 20 mg of powder catalyst mixed in tight contact with soot.Under these conditions, the SCR reaction that is carried out at a GHSV of ca.900,000 h −1 results in a lower NO x conversion than that observed previously.This downscale of the catalytic bed was necessary to reduce pressure drop issues originating by mixing a higher amount of catalyst with soot in powder form.Figure 6 shows that for 8.4 wt % catalysts, the comparison of NO conversion obtained under the conditions described above in SCR and SCR/de-soot reaction.In addition, the CO 2 concentration profile due to soot combustion is also reported.In agreement with the results obtained with lower space velocity (Figure 5), SCR only reaction (blue curve in Figure 6), shows a typical volcano shape with a maximum conversion in the range 350-400 • C. Iron vanadates over TWS support are the best performing catalytic materials with a maximum NO conversion in the range 40-60% while a drop to lower conversion values is observed using CeO 2 and CeZrO 2 as supports (16-18%).In correspondence of CO 2 evolution peak, a decrease of NO conversion is observed, which is much more evident for CZ based supports.Similar results are obtained with CeO 2 (supplementary material Figure S5).NH 3 evolution profiles (not shown) reveal a decrease in NH 3 concentration in correspondence to soot oxidation that indicates a large consumption of ammonia to form NO. On pure FeVO 4 and Ce 0.75 Zr 0.25 O 2 , negative NO conversion values are obtained (Figure 7).This indicates that NO can be generated through ammonia oxidation, and this occurs in correspondence to carbon soot oxidation.Monitoring catalyst temperature during heating ramp allowed to exclude that a local increase of temperature during carbon oxidation might affect reaction mechanism (Figure S6, Supplementary).A similar result, that better highlights the decrease of NO conversion in SCR, is found when running the fast-SCR with NO 2 present in the feed gas on bare Ce 0.75 Zr 0.25 O 2 mixed with soot.In this case, the high NO conversion observed already at 150 • C, drops in correspondence of soot oxidation and CO 2 release (Figure 7D).Interestingly, a small drop in NO conversion in correspondence to soot oxidation is observed also on pure FeVO 4 and TWS (Figure 7A,B) which indicates that soot oxidation slightly affects NH 3 -SCR also on these compounds.For this reason, ammonia oxidation reaction was studied for the single catalyst components.In Figure 8, NH 3 oxidation results over FeVO 4 , TWS, CeO 2 , Ce 0.75 Zr 0.25 O 2 are shown.The four different profiles compare reaction carried out with empty reactor, and with reactor filled with soot, catalyst and soot/catalyst mixtures.Compared to the empty reactor, soot alone has a minimal effect towards ammonia oxidation, as already observed by Mehring et al. [33].FeVO 4 is the most active in the oxidation of NH 3 , followed by ceria and ceria-zirconia.For FeVO 4 , there is no large difference in NH 3 oxidation activity with or without the presence of soot.For CeO 2 and Ce 0.75 Zr 0.25 O 2 instead, the tight contact with soot (Figure 8C,D-red lines) leads to an additional NH 3 consumption in correspondence of CO 2 release due to soot combustion.This consumption is higher than the sum of contributions of catalyst and soot alone, showing a synergistic effect of the two components in NH 3 oxidation reaction and indicating that the presence of carbon soot on CeO 2 and CeZrO 2 produces a synergic effect increasing NH 3 oxidation to NO.No significant effect is displayed in NH 3 oxidation reaction by CeVO 4 which is formed on these catalysts when FeVO 4 is supported on CeO 2 as highlighted in Figure S7 in supplementary material.This effect is the responsible of the large decrease in NO conversion observed over ceria-containing materials in NH 3 -SCR reaction.

Catalyst Preparation
FeVO 4 and Fe 0.5 Er 0.5 VO 4 were prepared by co-precipitation of metal nitrates (Fe(NO 3 ) 3 •9H 2 O and Er(NO 3 ) 3 •6H 2 O, Treibacher Industrie AG, Althofen, Austria)) and ammonium metavanadate (99+%, Sigma-Aldrich, St. Louis, MO, USA).Aqueous solutions of the precursors were separately prepared at 80 • C.After unification, the pH was adjusted by means of ammonia (28% aqueous solution, Sigma-Aldrich) to obtain the respective precipitate which was filtered, washed and dried at 120 • C overnight.These vanadates were subsequently used to make the supported catalysts.All support used in this study were commercial materials (CeO 2 from Treibacher Industrie AG, CeZrO 2 from W.R. Grace (Columbia, MD, USA), TWS from Cristal (Hong Kong, China), Al 2 O 3 from Sasol Germany GmbH (Hamburg, Germany)).Supported catalysts were prepared by mixing two separate aqueous slurries containing, respectively, the vanadate and the support.Vanadate/support weight ratio was 8.4/91.6 or 50/50.Combined slurries were evaporated to dryness.The resulting solids were dried at 120 • C overnight followed by calcination at 650 • C/2 h in a muffle furnace to obtain the final catalyst.

Catalytic Tests
Soot combustion efficiency under air was measured by means of thermogravimetry using soot (Printex U-Degussa)/catalyst mixtures under tight contact conditions obtained by mixing the two components in an agate mortar for 10 min.The soot/catalyst weight ratio was 1:20.The samples were placed on Pt crucibles licked by air flow (60 mL/min) and heated at a constant rate of 10 • C/min from RT up to 800 • C. T50 values, corresponding to the temperature at which 50 wt % of carbon is lost, was used as a measure of soot oxidation activity.Soot oxidation under NO/O 2 /N 2 and NO/O 2 /N 2 /NH 3 was carried out in a laboratory set-up equipped with a quartz microreactor for powder testing.In these experiments 20 mg of sample in powder form (soot/catalyst ratio of 20:1, mixed in tight contact) were exposed to a 300 mL/min feed stream of composition 500 ppm NO, 500 ppm NH 3 (when present), 10% O 2 , 5% H 2 O, balance N 2 with a GHSV of 900,000 h −1 .
NH 3 -SCR activity was measured in the same laboratory set-up described above on 100 mg of catalyst pressed and sieved (350 < Ø < 425 µm) under a 300 mL/min feed stream of composition 500 ppm NO, 500 ppm NH 3 , 10% O 2 , 5% H 2 O, balance N 2 with a GHSV of 180,000 h −1 .
NH 3 oxidation experiments were conducted on 20 mg catalytic beds under a reactive atmosphere of composition 500 ppm NH 3 , 10% O 2 , balance N 2 with a GHSV of 900,000 h −1 .Ammonia concentration was monitored during a temperature ramp from 150 • C up to 650 • C. When soot was present, also CO 2 release due to carbon oxidation was monitored.
For all experiment conducted in the gas bench, the composition of the feed stream (reagents and products) was analyzed with an on line MKS 2030 MultiGas Analyzer FT-IR instrument.

Characterization of the Catalysts
Specific surface areas of catalysts were measured by nitrogen adsorption at -196 • C according to the B.E.T. method on a Tristar 3000 gas analyzer (Micromeritics, Norcross, GA, USA).Prior to the measurement all samples were outgassed at 150 • C for 1.5 h.Powder X-ray diffraction patterns were collected on a Philips X'Pert diffractometer (PANalytical B.V., Almelo, The Netherlands) operated at 40 kV and 40 mA using Ni filtered Cu Kα radiation.Data were recorded from 10 to 100 • 2θ using a step size of 0.02 • and a counting time of 40 s per angular abscissa.Phase identification was conducted with the Philips X'Pert Highscore software (PANalytical B.V., Almelo, The Netherlands, 2002).Reducibility of the samples was measured by temperature programmed reduction (TPR) runs; approximately 50 mg of samples were heated at 10 • C/min in a U-shaped quartz reactor from room temperature up to 960 • C under a 4.5 vol % H 2 /N 2 flow (35 mL/min).The samples were pretreated at 500 • C for 1 h under air flow.Hydrogen consumption was monitored with a thermal conductivity detector (TCD) in an Autochem II 2920 instrument (Autochem II 2920, Micromeritics, Norcross, GA, USA).Raman spectra were collected with a Xplora Plus Micro-Raman system (Horiba, Kyoto, Japan) equipped with a cooled CCD detector (−60 • C) and Edge filter.The samples were excited with the 512 nm radiation in a Linkam CR1000 in situ cell at 200 • C under flowing air.The spectral resolution was 1 cm −1 and the spectra acquisition was of 5 accumulations of 10 or 20 s with a 50× LWD objective.The optical images were collected with an integrated microscope Olympus BX43 (Olympus, Tokyo, Japan) with a 10× objective.

Conclusions
A systematic screening to evaluate the interaction between soot oxidation and NH 3 -SCR has been carried out investigating the behavior of FeVO 4 and Fe 0. Al 2 O 3 -based materials are almost inactive either in SCR and soot oxidation while, as expected, TiO 2 -based materials are highly active in NH 3 -SCR and CeO 2 /CeZrO 2 are active in carbon soot oxidation.The addition of ammonia is found to slightly influence soot oxidation by reducing its combustion temperature by a few degrees while the presence of soot is found to affect SCR reaction, especially in the presence of CeO 2 and CeZrO 2 .This is due to the combined effect of the catalyst and carbon soot that results in an enhancement of NH 3 oxidation reaction.

Figure 2 .
Figure 2. Raman spectra of 8.4 wt % FeVO 4 /TWS (TiO 2 -WO 3 -SiO 2 ).The blue line represents Raman spectrum of a light spot on the sample (blue circle in the optical image) where anatase and surface VO x (blue arrows) were detected; the red line is the spectrum of a red spot (red arrows in the optical image) showing mainly FeVO 4 and a band belonging to Fe 2 O 3 (green arrow in the Raman spectrum).

Figure 4 .
Figure 4. Effect of vanadate loading on soot oxidation activity.

Figure 7 .
Figure 7. SCR runs on single components of the catalysts.Blue lines represent SCR of the bare samples, red lines represent SCR activity of the samples in tight contact with soot, black lines represent CO 2 production during soot combustion.(A) FeVO 4 ; (B) TWS; (C) Ce 0.75 Zr 0.25 O 2 standard SCR; (D) Ce 0.75 Zr 0.25 O 2 fast SCR.

5
Er 0.5 VO 4 loaded on standard SCR supports like TiO 2 -WO 3 -SiO 2 , redox active carriers like CeO 2 or Ce 0.75 Zr 0.25 O 2 and Al 2 O 3 .It is shown by combined XRD, TPR, and Raman spectroscopy that vanadates partially decompose over TiO 2 -based materials and Al 2 O 3 with formation of Fe 2 O 3 and surface VO x species.In the presence of CeO 2 /CeZrO 2 , formation of crystalline CeVO 4 along with Fe 2 O 3 is reported.

Supplementary Materials:
The following are available online at http://www.mdpi.com/2073-4344/8/4/130/s 1, Figure S1: Raman spectra of 8.4 wt % FeVO 4 /Al 2 O 3 .In the blue line (grating 1800 L/mm with 5 s per accumulation) only Fe 2 O 3 and Al 2 O 3 Raman shifts are visible.Surface VO x could not be detected.In the red line Raman shifts mainly attributable to FeVO 4 and Fe 2 O 3 are shown, Figure S2: XRD patterns of (A) 50 wt % FeVO 4 and (B) 50 wt % FeErVO 4 on different supports.Figure S3: Raman spectra of 50 wt % FeVO 4 /TWS.The optical image of the sample shows that the dark spots of FeVO 4 and Fe 2 O 3 are uniformly distributed and all Raman spectra show the Raman shifts of FeVO 4 .Figure S4: Effect of FeErVO 4 loading on soot oxidation activity, Figure S5: Comparison of SCR catalytic activity of 20 mg catalytic beds of bare catalysts and with soot oxidation conducted simultaneously, Figure S6: Comparison between theoretical heating ramp and temperature measured in the catalyst bed during soot oxidation reaction on CeO 2 sample (tight contact, soot/catalyst weight ratio of 1:20), Figure S7: NH 3 oxidation carried out on single catalyst components under the following conditions: catalyst 20 mg, NH 3 500 ppm, O 2 10%, N 2 balance, GHSV 900,000 h −1 , Table S1: B.E.T. surface areas of Fe 0.5 Er 0.5 VO 4 catalysts.

Table 1 .
B.E.T. surface areas, hydrogen consumption in TPR, H/V atomic ratio and onset temperature of reduction for each sample.
1Calculated on the basis of H 2 consumption from TPR profiles and total vanadium content of the catalyst.

Table 2 .
Soot oxidation characteristic temperatures of investigated catalysts.
1Temperature of 50% weight loss measured in thermogravimetric temperature programmed ramps from RT up to 800 • C on catalyst samples mixed in tight contact with soot.2Peaktemperaturecalculated from CO 2 profiles during TPO (Temperature Programmed Oxidation) runs in a flow-trough microreactor under 500 ppm NO, 10% O 2 , (balance N 2 ) atmosphere.3Peak temperature calculated from CO 2 profiles during TPO runs in a flow-trough microreactor under 500 ppm NO, 500 ppm NH 3 , 10% O 2 , 5% H 2 O, (balance N 2 ) atmosphere.