Fe/Fe cycling promoted by Ta3N5 under visible irradiation in Fenton degradation of organic pollutants

Ta₃N₅ was synthesized by nitridation of Ta₂O₅ under NH₃ flow at 700 °C. The catalyst was pure Ta₃N₅ according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m²/g. When Ta₃N₅ was added to Fe³⁺/H₂O₂ solution (known as Fenton-like system), most Fe³⁺ were adsorbed on the Ta₃N₅ surface and could not react with H₂O₂ in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe³⁺ ions were reduced to Fe²⁺ rapidly and Fe²⁺ were reoxidized by H₂O₂ on the Ta₃N₅ surface, thus a fast Fe³⁺/Fe²⁺ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta₃N₅/Fe³⁺/H₂O₂ system could efficiently decompose H₂O₂ to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N,N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results.     

Characterization and catalytic investigation of Fe-ZSM5 for urea-SCR

Fe-ZSM5 was prepared with high iron content by solid-state ion exchange and characterized by ICP-AES, BET surface measurements, TEM, UV–vis, EPR and DRIFT spectroscopy as well as supplementing catalytic tests in order to clear up its functionality in urea-SCR. Due to the over-exchange with iron small Fe₂O₃ particles were formed, identified by UV–vis, EPR and TEM measurements, which were proved to be not active for the SCR reaction. However, the oxidation of NO to NO₂ over Fe³⁺ ions in the catalyst was realized to be a pre-requisite for the SCR reaction and the rate-determining step. DRIFT investigations under SCR conditions showed adsorbates on Fe²⁺ up to 300 °C. The high SCR activity above 300 °C can be explained by the faster reoxidation of Fe²⁺ to Fe³⁺ sites at high temperatures. The observed inhibition of the SCR reaction by excess ammonia at low and intermediate temperatures can be explained in this context by the reducing properties of ammonia converting Fe³⁺ to Fe²⁺ or by preventing the reoxidation of Fe²⁺.     

Absence of E. coli regrowth after Fe and TiO2 solar photoassisted disinfection of water in CPC solar photoreactor

Field disinfection of water in a large solar compound parabolic collector (CPC) photoreactor (35–70 l) was conducted at 35 °C by different photocatalytic processes: sunlight/TiO₂, sunlight/TiO₂/Fe³⁺, sunlight/Fe³⁺/H₂O₂ and compared to the control experiment of direct sunlight alone. Experiments were carried out using a CPC and natural water spiked with E. coli K 12. Under these conditions, total disinfection by bare sunlight irradiation was not reached after 5 h of treatment; and bacterial recovery was observed during the subsequent 24 h in the dark.

The addition of TiO₂, TiO₂/Fe³⁺ or Fe³⁺/H₂O₂ to the water accelerates the bactericidal action of sunlight, leading to total disinfection by solar-photocatalysis. No bacterial regrowth was observed during 24 h after stopping sunlight exposure. For some samples, the decrease of bacteria continues in the dark. A “residual disinfection effect” was observed for these samples before reaching the total inactivation. The effective disinfection time (EDT₂₄), defined as the treatment time required to prevent any bacterial regrowth during the subsequent 24 h in the dark, after stopping the phototreatment, was reached in the presence but not in the absence of different photocatalytic systems. EDT₂₄ was 2 h 30 min, 2 h and 1 h 30 min for sunlight/TiO₂, sunlight/TiO₂/Fe³⁺ and sunlight/Fe³⁺/H₂O₂ systems, respectively. The post irradiation events observed when the phototreated water is poured into an optimal growth medium are also discussed.     

Influence of isovalent and aliovalent substitutions at Ti site on bismuth sodium titanate-based compositions on piezoelectric properties

The effect of isovalent and aliovalent substitutions in Bi_0.5Na_0.485La_0.005TiO₃ (BNLT) compounds were studied within the additive ranges of 0–2.5 at%. The Zr⁴⁺, Nb⁵⁺ and Fe³⁺ ions were selected as the substituents. The modified BNLT compounds were prepared by conventionally mixed-oxide method. The calcination and sintering were performed at the temperatures of 750–850 °C and 1050–1150 °C, respectively. An increase in the substituents contents affected the physical and piezoelectric properties. The BNLT compositions with the addition of 1 at% Zr⁴⁺, Nb⁵⁺ and Fe³⁺ ions exhibited high relative permittivities (_r) at 730, 735 and 660, respectively. The modified-BNLT with an addition of 1.0 at% Fe provided a piezoelectric coefficient (d₃₃) of 155 pC/N, Curie temperature (T_c) of 320 °C and electromechanical coupling factors in planar (k_p) and thickness (k_t) modes of 15 and 45%, respectively.     

Effective Au-Au-Clx/Fe(OH)y catalysts containing Cl for selective CO oxidations at lower temperatures

Supported Au catalysts Au-Au⁺-Cl_x/Fe(OH)_y (x < 4, y ≤ 3) and Au-Cl_x/Fe₂O₃ prepared with co-precipitation without any washing to remove Cl⁻ and without calcining or calcined at 400 °C were studied. It was found that the presence of Cl⁻ had little impact on the activity over the unwashed and uncalcined catalysts; however, the activity for CO oxidation would be greatly reduced only after Au-Au⁺-Cl_x/Fe(OH)_y was further calcined at elevated temperatures, such as 400 °C. XPS investigation showed that Au in catalyst without calcining was composed of Au and Au⁺, while after calcined at 400 °C it reduced to Au⁰ completely. It also showed that catalysts precipitated at 70 °C could form more Au⁺ species than that precipitated at room temperatures. Results of XRD and TEM characterizations indicated that without calcining not only the Au nano-particles but also the supports were highly dispersed, while calcined at 400 °C, the Au nano-particles aggregated and the supports changed to lump sinter. Results of UV–vis observation showed that the Fe(NO₃)₃ and HAuCl₄ hydrolyzed partially to form Fe(OH)₃ and [AuCl_x(OH)_4−x]⁻ (x = 1–3), respectively, at 70 °C, and such pre-partially hydrolyzed iron and gold species and the possible interaction between them during the hydrolysis may be favorable for the formation of more active precursor and to avoid the formation of Au–Cl bonds. Results of computer simulation showed that the reaction molecular of CO or O₂ were more easily adsorbed on Au⁺ and Au⁰, but was very difficultly absorbed on Au⁻. It also indicated that when Cl⁻ was adsorbed on Au⁰, the Au atom would mostly take a negative electric charge, which would restrain the adsorption of the reaction molecular severely and restrain the subsequent reactions while when Cl⁻ was adsorbed on Au⁺ there only a little of the Au atom take negative electric charge, which resulting a little impact on the activity.     

Changes in states of substituted iron in microporous (MFI analogue) and mesoporous (MCM-41) hosts exposed to redox conditions

Iron was incorporated into microporous MFI analogue (ZSM-5, Si/Fe  200 and FER, Si/Fe = 16) and mesoporous MCM-41 hosts of different preparations (Si/Fe  100 and 20, respectively). Samples were characterized by in situ Mössbauer spectroscopy under various conditions. Framework (FW) and extra-framework (EFW) sites can be distinguished in relation with strict three-dimensional (3D) crystallinity of the structure. In addition, in the microporous ZSM-5 system occurrence of Fe⁴⁺ oxidation state is hypothesized and reversible Fe⁴⁺ ↔ Fe³⁺ transformation is presumed for a minor portion of iron. Spectra of Fe-FER are interpreted in terms of dynamic formation and decomposition of Fe_FW–O–Fe_EFW dinuclear centres. In the mesoporous systems, the partly amorphous character of the pore wall is correlated with the redox behaviour and coordination of incorporated iron; larger portion of iron may take part in Fe³⁺ ↔ Fe²⁺ reversible processes and Fe²⁺ may be stabilized in distorted coordination (not appearing in microporous structures).     

Preparation of supported Pt-M catalysts (M = Mo and W) from anion-exchanged hydrotalcites and their catalytic activity for low temperature NO-H2-O2 reaction

The NO-H₂-O₂ reaction was studied over supported bimetallic catalysts, Pt-Mo and Pt-W, which were prepared by coexchange of hydrotalcite-like Mg-Al double layered hydroxides by Pt(NO₂)₄²⁻, MoO₄²⁻, and/or WO₄²⁻ and subsequent heating at 600 °C in H₂. The Pt–Mo interaction could obviously be seen when the catalyst after reduction treatment was exposed to a mixture of NO and H₂ in the absence of O₂. The Pt-HT catalyst showed the almost complete NO conversion at 70 °C, whereas the Pt-Mo-HT showed a negligible conversion. Upon exposure to O₂, however, Pt-Mo-HT exhibited the NO conversion at the lowest temperature of ≥30 °C, compared to ≥60 °C required for Pt-HT. EXAFS/XANES, XPS and IR results suggested that the role of Mo is very sensitive to the oxidation state, i.e., oxidized Mo species residing in Pt particles are postulated to retard the oxidative adsorption of NO as NO₃ and promote the catalytic conversion of NO to N₂O at low temperatures.     

Role of iron surface oxidation layers in decomposition of azo-dye water pollutants in weak acidic solutions

While decomposition of water pollutants in the presence of metallic iron can be strongly influenced by the nature and structure of the iron surface layer, the composition and structure of the layer produced and transformed in the decomposition process, have been meagerly investigated. The studies presented here establish strong relationships between the composition and structure of the iron oxidized surface layer and the kinetics and reaction pathways of orange II decomposition. The most striking observation is a dramatic difference between dye decomposition at pH 3 and 4. Orange decomposition at pH 2 and 3 is a very fast process with pseudo-first-order kinetics, with a surface normalized rate constant k_SA = 0.18 L/m² min at pH 3 and 30 °C. Whereas at pH 4 and 5 the rate is lower with pseudo-zero-order kinetics, with normalized rate constant k_SA = 1.4 × 10⁻⁵ mol/m² min at pH 5 and 30 °C. At pH 3 the iron surface is covered by a polymeric Fe(OH)₂ mixed with FeO very thin layer whose thickness remains almost constant with reaction time. There is a slow formation of an additional surface product with akaganeite-like structure. At pH 3 almost all oxidized iron is detected in solution, whereas at pH 5 almost total oxidized iron is cumulated on iron surface in the form of a lepidocrocite, γ-FeOOH, layer. The thickness of the layer increases continuously with time. The quantitative evaluation of the produced surface lepidocrocite and its surface distribution were performed by means of infrared reflection spectroscopy and spectral simulation methods. At higher temperature 40–50 °C, other surface products such as goethite, -FeOOH, and feroxyhite, β-FeOOH, are also observed. Decomposition of orange is a multi-step process, at pH 3 the orange molecule is at first adsorbed on the very thin iron oxidized layers through SO₃ group and then undergoes reduction. Discoloration of orange II in aerobic solution takes place by reduction of the NN bond at the iron surface. The major intermediate is 1-amino-2-naphtol, which undergoes further decomposition without forming any aromatic species. The previously suggested sulfanilic acid as intermediate was not detected in solution. At pH 3 orange reduction and reduction of intermediates are governed by the combination of an electron transfer reaction, with the thin oxide surface layer as a mediator, and the catalytic hydrogenation reaction. At pH 4 and 5 continuous growing of lepidocrocite surface layer demonstrates the importance of the layer as a mediator in the electron transfer reaction. The layer shows a good conductivity, which results from adsorption and absorption of iron ions in the surface structure. It is observed that the decomposition reaction becomes significant at open circuit potential (OCP) below −120 mV (SHE). At pH 3 this condition is fulfilled almost immediately after introduction of iron to aqueous solution, whereas at pH 4 and 5 the OCP of iron decreases very slowly. Iron surface layer composition and structure can be modified by an addition of Fe²⁺ to solution, which increases the dye decomposition rate. The performed observations make the treatment of waste water in the presence of metallic iron a promising environmental solution.     

Deactivation of a Fe-ZSM-5 catalyst during the selective catalytic reduction of NO by n-decane: An operando DRIFT study

The selective catalytic reduction (SCR) of NO by n-decane was investigated on a Fe-ZSM-5 prepared by the FeCl₃ sublimation method. NO conversion profiles versus temperature were followed in both temperature programmed surface reaction (TPSR, 10 °C min⁻¹) and steady state experiments. A higher NO conversion with a maximum of ca. 80% at 400 °C is observed in the course of the TPSR tests. This phenomenon has been attributed to strong adsorption of n-decane which protects the active sites against the poisoning. Indeed, in steady state experiments at 390 °C the strong decrease of activity as a function of time on stream is due to the polymerisation of conjugated nitriles. This study indicates that long chain alkanes are not the most adequate reductants of NO for high temperature SCR applications. Moreover, due to an easier polymerization of conjugated nitriles on iron zeolites (stronger Fe Lewis sites), this type of catalyst seems less attractive than Cu-zeolite catalysts for the SCR of NO by hydrocarbons in this respect.     

Microwave-hydrothermally aged Zn,Al hydrotalcite-like compounds: Influence of the composition and the irradiation conditions

Zn,Al–CO₃ compounds with the hydrotalcite-like (layered double hydroxide, LDH) structure were prepared by a co-precipitation method followed by hydrothermal treatment under microwave irradiation. The influence of the ageing treatment was studied in two series of samples with different Zn²⁺/Al³⁺ ratios, namely, 3/1 and 2/1. Moreover, the effects of the heating temperature and of the irradiation time were studied in order to select the optimum preparation conditions. The solids were fully characterised by powder X-ray diffraction (PXRD), ²⁷Al MAS-NMR, FT-IR spectroscopy, thermal analyses (DTA and TG), N₂ adsorption/desorption at −196 °C and TEM. The results showed that whatever the chemical composition of the starting mixture, HTlcs with Zn²⁺/Al³⁺ ratio equal to 2 were obtained, and it was impossible to overcome the ZnO segregation when the molar ratio was >2. These compounds were stable and their crystallinity could be quickly enhanced when the temperature treatment was 100 °C, whereas at 125 °C the ZnO segregation was not prevented.     

Novel route of synthesis of Mn---Mg---ferrites using stabilised MnO

Stoichiometric polycrystalline samples of Mn_xMg_1−xFe₂O₄ (0·5 ≤ x ≤ 0·66) have been synthesized by following a novel route using stabilized MnO and Fe₂O₃ at high temperatures. This route precludes the formation of large amounts of Mn³⁺ and Fe²⁺ and precipitation of MgO and -Fe₂O₃ which are generally observed during the usual route of preparation by conventional ceramic techniques. These samples have been characterized for their structural and magnetic properties using X-ray diffraction, Fe⁵⁷ Mössbauer spectroscopy and bulk magnetic properties such as initial permeability, loss factor, ferromagnetic transition temperature, remanance and coercivity. For X = 0·62, these ferrites exhibit the highest remanance ratio 0·96, suitable for square loop applications.     

Removal of hydrogen sulfide by clinoptilolite in a fixed bed adsorber

Due to its toxic and corrosive nature, H₂S should be safely removed from the gases produced in gasification or combustion processes. In this study, adsorption of hydrogen sulfide was investigated on a natural zeolite, namely clinoptilolite. H₂S adsorption characteristics of Western Anatolian clinoptilolite was studied in a fixed-bed system at different temperatures between 100 and 600 °C at atmospheric pressure. H₂S adsorption capacity of clinoptilolite was found to be about 0.03 g S/g clinoptilolite at 600 °C. A deactivation model considering concentration dependence of activity term was applied to experimental results and adsorption rate constant and activation energy values were evaluated. Good agreement of the experimental breakthrough curves with the model predictions was observed.     

Kinetics and mass transfer effects in the oxidation of ferrous sulfate over doped active carbon catalysts

Ferric sulfate is used in water purification. The oxidation of ferrous sulfate, FeSO₄, to ferric sulfate in acidic aqueous solutions of H₂SO₄ over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and two kinds of catalysts were utilized: active carbon, doped active carbon. Both active carbon and doped active carbon catalysts enhanced the oxidation rate considerably.

Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60–100°C and 4–10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe²⁺ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe²⁺ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe²⁺ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe²⁺ over pure active carbon and doped active carbon catalysts.     

Phenol hydroxylation using Fe-MCM-41 catalysts

Highly ordered iron-containing mesoporous material, Fe-MCM-41, with 0.5–4 Fe/Si mol% loading was prepared and characterization was performed using XRD, SEM/TEM, EDS, N₂-sorption, and FT-IR and UV–vis spectroscopies. Fe-MCM-41 exhibited high catalytic activity in phenol hydroxylation using H₂O₂ as oxidant, giving phenol conversion of ca. 60% at 50 °C [phenol:H₂O₂ = 1:1, water solvent]. Effects of Fe contents in Fe-MCM-41 and catalyst concentration, temperature, solvent used, phenol/H₂O₂ mole ratios and H₂O₂ feeding method, and catalyst calcination temperature on conversion profiles were examined. Catalyst recycling was performed to investigate the extent of potential metal leaching. Comparisons in performance were also made using nano-sized Fe₂O₃ particles and Fe-salt impregnated MCM-41 as catalyst. Catechol to hydroquinone in product ratio was close to 2:1 in accordance with a free radical reaction scheme involving Fe²⁺/Fe³⁺ redox pair and the larger amount of Fe species always achieved the given phenol conversion at a shorter reaction time. As the calcination temperature increases from 400 to 800 °C increasing amount of Fe species came out from the MCM-41 framework. Both tetrahedral Fe and extra-framework Fe species were found catalytically active, but high dispersion of Fe species achieved in Fe-MCM-41 was an advantage.     

Hallspannungsmessungen in wässrigen elektrolyten

In measuring the Hall effect in aqueous solutions some aspects of electrochemistry and electrode kinetics have to be considered. The described apparatus is based on a constant magnetic field and an alternating electrical field of variable frequency and on three Hall electrodes. The hall mobility in 0·1 N HNO₃, 0·01 N AgNO₃ at 20°C is 2·58 × 10⁻³ cm/Vs.

Résumé

Quelques aspects électrochimiques et électrocinétiques des mesures de l'effet Hall dans les solutions aqueuses sont discutés. L'apparaillage décrit en détail fonctionne au moyen d'un champ magnétique continu, d'un champ électrique alternatif de fréquence variable et avec trois sondes d'Hall. La mobilité d'Hall trouvée dans un électrolyte de 1/10 n HNO₃, 1/100 n AgNO₃ est = 2,58 · 10⁻³ cm²/Vs à 20°C.     

Microemulsion synthesis of MgO-supported LaMnO3 for catalytic combustion of methane

Catalysts with 20% LaMnO₃ supported on MgO have been prepared via CTAB-1-butanol-iso-octane-nitrate salt microemulsion. The preparation method was successfully varied in order to obtain different degrees of interaction between LaMnO₃ and MgO as shown by TPR and activity tests after calcination at 900 °C. Activity was tested on structured catalysts with 1.5% CH₄ in air as test gas giving a GHSV of 100,000 h⁻¹. The activity was greatly enhanced by supporting LaMnO₃ on MgO compared with the bulk LaMnO₃. After calcination at 1100 °C both the surface area and TPR profiles were similar, indicating that the preparation method is of little importance at this high temperature due to interaction between the phases. Pure LaMnO₃ and MgO were prepared using the same microemulsion method for comparison purposes. Pure MgO showed an impressive thermal stability with a BET surface area exceeding 30 m²/g after calcination at 1300 °C. The method used to prepare pure LaMnO₃ appeared not to be suitable since the surface area dropped to 1.1 m²/g already after calcination in 900 °C.     

In situ FTIR characterization of the adsorption of CO and its reaction with NO on Pd-based FCC low NOx combustion promoters

The adsorption of CO and its reaction with NO in the 400–600 °C temperature range on Ceⁿ⁺/Na⁺/γ-Al₂O₃ and Pdⁿ⁺/Ceⁿ⁺/Na⁺/γ-Al₂O₃ type materials used commercially as FCC additives were monitored by FTIR spectroscopy. Exposure of both types of samples to CO leads to the formation of carboxylates and carbonates. The concentration of these species was higher in samples containing Pd, indicating that palladium catalyzes their formation. The Pdⁿ⁺ cations initially present in these samples undergo partial reduction to form metallic Pd in the presence of CO even at room temperature. More complete reduction of Pd, along with some aggregation, was observed after exposure to CO at elevated temperatures. Exposure of both types of samples to NO/CO mixtures in the 400–600 °C temperature range leads to the formation of surface isocyanate species. Both Na⁺ and Ceⁿ⁺ promote the formation of such NCO species. However, surface isocyanate species were formed with substantially higher rates in the presence of palladium. The formation of the isocyanate species strongly correlates with changes observed in the ν_OH region, indicating that hydroxyls actively participate in the surface chemistry involved and are capable of protonating the NCO species. The isocyanates are also reactive towards O₂ and NO yielding CO₂ and N₂. These results suggest that isocyanates are possibly involved as intermediates in the CO–NO reaction over the materials examined.     

Physicochemical surface and catalytic properties of CuO–ZnO/Al2O3 system

A series of CuO–ZnO/Al₂O₃ solids were prepared by wet impregnation using Al(OH)₃ solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O₂ at temperatures ranged between 125°C and 200°C.

The results showed that CuO interacts with Al₂O₃ to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl₂O₄ at 600°C while stimulates its production at 800°C. The treatment of CuO/Al₂O₃ solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol⁻¹ in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature.     

Regeneration of NOx trap catalysts

We have investigated the regeneration of a nitrated or sulphated model Pt/Ba-based NO_x trap catalyst using different reductants. H₂ was found to be more effective at regenerating the NO_x storage activity especially at lower temperature, but more importantly over the entire temperature window after catalyst ageing. When the model NO_x storage catalyst is sulphated in SO₂ under lean conditions at 650 °C almost complete deactivation can be seen. Complete regeneration was not achieved, even under rich conditions at 800 °C in 10% H₂/He. Barium sulphate formed after the high temperature ageing was partly converted to barium sulphide on reduction. However, if the H₂ reduced sample was exposed to a rich condition in a gas mixture containing CO₂ at 650 °C, the storage activity can be recovered. Under these rich conditions the S²⁻ species becomes less stable than the CO₃²⁻, which is active for storing NO_x. Samples which were lean aged in air containing 60 ppm SO₂ at <600 °C, after regeneration at λ=0.95 at 650 °C, have a similar activity window to a fresh catalyst. It is, therefore, important that CO₂ is present during the rich regenerations of the sulphated model samples (as of course it would be under real conditions), as suppression of carbonate formation can lead to sulphide formation which is inactive for NO_x storage.     

Combined CO/CH4 oxidation tests over Pd/Co3O4 monolithic catalyst: Effects of high reaction temperature and SO2 exposure on the deactivation process

CO and CH₄ combined oxidation tests were performed over a Pd (70 g/ft³)/Co₃O₄ monolithic catalyst in conditions of GHSV = 100,000 h⁻¹ and feed composition close to that of emission from bi-fuel vehicles. The effect of SO₂ (5 ppm) on CO and CH₄ oxidation activity under lean condition (λ = 2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co₃O₄ catalytic sites via chemisorbed SO₃ and/or sulphates occurred upon exposure to SO₂. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900 °C in oxidizing atmosphere. Decomposition of PdO and Co₃O₄ phases at high temperature, above 750 °C, was observed. Moreover, sintering of Pd⁰ and PdO particles along with of CoO crystallites takes place.