Pd Metal Particles Research Articles

Light‐off Performance of Three‐Way Catalysts Before and After Accelerated Aging Test with an Engine‐Dynamometer

AbstractThis study demonstrates the reaction behavior during the purification of model automotive exhaust gases over Pd catalysts before and after thermal degradation. In particular, to investigate the relationship between the Pd state and the reaction behavior of Pd/Al2O3 and Pd/CeO2−ZrO2 (CZ), operando X‐ray absorption spectroscopy measurements were performed during purifying exhaust gases over real and model catalysts mimicking the degradation of Pd particles and CZ supports after accelerated aging tests. The NO reduction activity of the aggregated Pd metal species was as high as that of the highly dispersed Pd species, but hydrocarbon (HC) poisoning was significantly enhanced by the aggregation of Pd metal particles caused by thermal aging. The existence of a three‐phase boundary (TPB) between the CZ, the Pd particles, and the gas phase strongly affected the catalytic activity at low temperatures, and the presence of a sufficient TPB facilitated the combustion of unburned HCs owing to the oxygen storage performance of CZ. Thus, the TPB reduced the poisoning of the precious metal surface by HC species at low temperatures. Therefore, the findings of this study will facilitate the development of next‐generation gas purification catalysts with high activity and durability.

Enhanced electrocatalytic activity of palladium electrocatalysts supported on corncob biochar for ethanol oxidation reaction in alkaline medium

AbstractIn this study, palladium particles supported on carbon black (Vulcan XC‐72) (Pd/C) and corncob biochar (Pd/CB800, Pd/CB900, and Pd/CB1000) were successfully synthesized using borohydride reduction. The biochar support was obtained from corncob waste via pyrolysis from 800 to 1000°C. Scanning electron microscopy with energy dispersive x‐ray (SEM–EDX) revealed successful deposition of Pd metal particles on the carbon support materials. X‐ray diffraction (XRD) analysis confirmed the crystalline structures of Pd, and the crystallite size was found to be smallest in Pd/CB900. The electrocatalytic activity of the Pd electrocatalyst composites towards ethanol oxidation reaction (EOR) in an alkaline medium was investigated using cyclic voltammetry (CV). CV analysis has shown that Pd/CB900 gave the least positive onset potential (Eonset = −0.587 ± 0.0065 V), highest electrochemically active surface area (EASA = 31.51 ± 2.24 m2·g−1), and highest anodic peak current density (If = 20.77 mA·cm−2) compared with Pd/CB800, Pd/CB1000, and Pd/C. Furthermore, the Tafel plot and chronoamperometry have shown that Pd/CB900 exhibited faster kinetics (Tafel slope = 297.6 ± 4.62 mV·dec−1) and durability (% current retention = 50.64 ± 2.99%) than Pd/C towards EOR in an alkaline medium. This study highlights the simple and straightforward synthesis of the anode electrocatalyst material for direct ethanol fuel cell application.

Palladium Encapsulated by an Oxygen‐Saturated TiO2 Overlayer for Low‐Temperature SO2‐Tolerant Catalysis during CO Oxidation

AbstractThe development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real‐working conditions. Herein, we describe the design and synthesis of oxide‐metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO2, an oxide/metal inverse catalyst with non‐classical oxygen‐saturated TiO2 overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra‐small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O2 and 10 vol % H2O). In particular, the core (Pd)‐shell (TiO2) structured OMI catalyst exhibited excellent resistance to SO2 poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO2 and 10 vol % H2O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd−O−Ti sites (of oxygen‐saturated overlayers) serve as non‐metal active sites for low‐temperature CO oxidation, and change the SO2 adsorption from metal(d)‐to‐SO2(π*) back‐bonding to much weaker σ(Ti−S) bonding.

Palladium Encapsulated by an Oxygen-Saturated TiO2 Overlayer for Low-Temperature SO2 -Tolerant Catalysis during CO Oxidation.

The development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real-working conditions. Herein, we describe the design and synthesis of oxide-metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO2 , an oxide/metal inverse catalyst with non-classical oxygen-saturated TiO2 overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra-small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O2 and 10 vol % H2 O). In particular, the core (Pd)-shell (TiO2 ) structured OMI catalyst exhibited excellent resistance to SO2 poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO2 and 10 vol % H2 O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd-O-Ti sites (of oxygen-saturated overlayers) serve as non-metal active sites for low-temperature CO oxidation, and change the SO2 adsorption from metal(d)-to-SO2 (π*) back-bonding to much weaker σ(Ti-S) bonding.

Eco-friendly production of palladium-modified γ-cyclodextrin and its methyl cinnamate inclusion complex: Catalyst for reduction and antibacterial properties

Addressing the conversion of toxic substances into non-toxic was a significant challenge in our environmentally compromised world. This manuscript focuses on elucidating the synthesis, chemical composition, and structure of a cinnamic acid (CA) derivative named methyl cinnamate (MC) using analytical techniques such as 1H NMR and FT-IR spectroscopy. Furthermore, we implemented an adapted synthetic procedure to effectively produce a modified version of γ-cyclodextrin known as palladium (Pd)-modified γ-CD (Pd-γ-CD). The Pd metal particles were uniformly distributed throughout the structure. The resulting product underwent characterization through a range of techniques, encompassing XRD, SEM, FT-IR, EDAX, TGA, and UV–visible spectroscopy. The UV–visible spectroscopy results confirmed the formation of a 1:1 inclusion complex between MC and both native γ-CD and Pd-γ-CD. Using the Benesi-Hildebrand equation and the Gibbs free energy relation, we calculated the binding constant and free energy change for the complex formation, respectively. The molecular interaction between Pd-γ-CD and MC was elucidated by 1H NMR and 2D NMR (ROESY) spectroscopy. Additionally, we investigated the catalytic reduction properties of our novel complexes, as well as native γ-CD and Pd-γ-CD, against 2,4-dinitrophenol. Notably, the Pd-γ-CD complex exhibited exceptional catalytic reduction performance. Moreover, we also evaluated the antibacterial effects of γ-CD, Pd-γ-CD, and their complexes against S. aureus and E. coli. The results indicated that the Pd-γ-CD complex showed superior efficacy against S. aureus bacteria compared to the other samples.

Promotion of catalytic performance of Pd/Al2O3 for o-xylene oxidation by morphological control

Pd/Al2O3 catalysts with different support morphologies (nanoflake, nanorod, nanobeam) were prepared and tested for o-xylene oxidation, and characterized by BET, XRD, TEM, XPS, NMR, CO-TPR-MS, H2-TPR and in-situ DRIFTS. The results indicated that the morphology has a strong effect on the dispersion of Pd species and the oxidation capacity of the catalysts. Compared with nanorod and nanobeam, the nanoflake morphology provides more surface defect sites, penta-coordinated Al3+ and surface OH species. Such sites (defect sites, AlP sites and OH species) enabled the immobilization of Pd to form Pd metal particles of small size, resulting in high Pd dispersion with primary exposure of Pd(100) facets possessing more defect sites for the adsorption. The OH species were also the adsorption sites. Both of them are conducive to the reactivity of adsorbed o-xylene. Moreover, the OH species on Pd/Al2O3 represented activated oxygen, indicating that o-xylene can be oxidized by OH directly. It means that these small Pd particles with more active surface OH species are responsible for the excellent catalytic performance of Pd/Al2O3-NF. Its o-xylene oxidation activity is much better than that of other Pd-based catalyst previously reported. Consequently, morphology control can manipulate Pd particle size and surface OH species to effectively improve the catalytic performance of Pd/Al2O3.

Highly efficient conversion of phenol to cyclohexanone on Pd-based catalysts by cobalt doping

Efficient catalysts are still the key to practical industrial applications. In this work, Pd-based catalyst was modified by doping metal Co to obtain Pd-Co@mSiO2 bimetallic core–shell catalyst. The modified bimetallic core–shell catalyst was used in the hydrogenation of phenol, and the catalytic results showed that the Co modification effectively improved the catalytic performance of the Pd-based catalyst, especially, it reduced the activation energy of the reaction and greatly improve the conversion of phenol. Combined with characterization, it was found that Co doping reduced the particle size of Pd metal particles and affected the adsorption capacity of substrate phenol on the surface of Pd metal. The conversion of phenol was close to 99.9 % within 1 h at 80 °C, while the selectivity of cyclohexanone reached 95.4 %. In addition, the core–shell structure provided a stable environment for the catalyst, which still maintained high activity after being recycled for 5 times.

Low temperature green methanol synthesis by CO2 hydrogenation over Pd/SiO2 catalysts in slurry reactor

The utilization of the greenhouse gas of carbon dioxide (CO2) for fuel and value-added chemicals synthesis has become globally indispensable process for healthy environment. In this context, the hydrogenation of CO2 to methanol is an attractive avenue for achieving such goal. Thus, we prepared mesoporous silica-supported nanocrystalline palladium metal (Pd) for methanol synthesis by CO2 hydrogenation. To investigate the role of Pd metal, the synthesized mesoporous silica was loaded with 1, 2, 3 and 4 wt% of Pd. Physicochemical profile of synthesized mesoporous silica supported Pd catalysts were assessed by Inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), Nitrogen adsorption–desorption and Temperature Program Reduction (TPR) techniques. ICP-OES measurement confirmed the actual Pd metal loading on the mesoporous silica support. XRD confirmed amorphous and crystalline nature of mesoporous silica and Pd metal, respectively. FESEM images exhibited homogenous and well dispersed Pd metal particles on the surface of mesoporuse silica support. Nitrogen adsorption desorption studies displayed enlargement in BET surface area with Pd promotion. Reduction behaviour of PdO was revealed by TPR data over the studied temperature range. The structure–activity studies suggested the degree of Pd crystallinity and higher dispersions as amongst the main factors contributing to the performance of Pd/SiO2 catalysts for pure CO2 hydrogenation in slurry reactor.

Effects of Treatment Conditions on Pd Speciation in CHA and Beta Zeolites for Passive NO x Adsorption.

The structure and evolution of Pd species in Pd-exchanged zeolite materials intended for use as passive NOx adsorbers were examined under various pretreatment conditions. Using in situ CO-diffuse reflectance infrared spectroscopy, Pd structures were characterized after 500 °C pretreatments in inert (Ar), water (1–2% H2O in Ar), oxidizing (air), and reducing (H2, CO) atmospheres. Two zeolites of similar Si/Al ratios but different framework topologies (Beta, CHA) were found to show different distributions of Pd species, depending on the reducing agent used. Reduction in H2 (500 °C; 10% H2 in Ar) followed by re-oxidation (500 °C; air) led to higher amounts of single-site Pd ions on Pd-CHA than Pd-Beta, whereas high-temperature reduction in CO (500 °C; 1000 ppm CO in Ar) followed by re-oxidation (500 °C; air) led to significant loss of ionic Pd on both Pd-CHA and Pd-Beta, albeit H2 temperature-programmed reduction and XPS experiments suggest that this phenomena may be limited to surface Pd. High-temperature treatments with water (500 °C; 1–2% H2O in Ar) are shown to form either Pd metal or PdO particles, with Pd-Beta being more susceptible to these effects than Pd-CHA. This work suggests that the effects of CO are especially problematic with respect to the durability of these materials in passive NOx adsorption applications, especially in the case of Beta zeolite.

Size, nanostructure, and composition dependence of bimetallic Au–Pd supported on ceria–zirconia mixed oxide catalysts for selective oxidation of benzyl alcohol

A bimetallic Au–Pd catalyst supported on ceria–zirconia with Au:Pd molar ratio 0.8 has been synthesized using a simultaneous deposition–precipitation method and oxidized at 250, 450, and 700 °C in order to modify its particle size, nanostructure, and composition. Combined X-ray energy dispersive spectroscopy (XEDS) and X-ray photoelectron spectroscopy (XPS) analysis clearly evidence that the bimetallic Au–Pd catalyst oxidized at 250 °C is made up of a mixture of monometallic Au and Pd and bimetallic Au–Pd nanoparticles with Au:Pd ratios varying over a wide range. Increasing oxidation temperature leads to a stronger interaction between Au and Pd. Meanwhile, a slight increase of particle size and a narrowing of the Au:Pd ratio in the bimetallic nanoparticles take place. Compared with titania and activated carbon supports, the resistance against sintering at high temperatures of Au–Pd metal particles supported on ceria–zirconia is proven to be higher. A synergistic effect has been observed for selective oxidation of benzyl alcohol on these catalysts. The catalytic activity decreases only slightly after oxidation at 450 °C. However, oxidation at 700 °C results in much lower catalytic activity. Migration of Pd onto Au particles during oxidation of benzyl alcohol enhances the catalytic activity of a physical mixture of monometallic Au and Pd supported on ceria–zirconia catalysts. This fact, jointly with an analysis of the intrinsic activity, reveals the influence of the actual nature of Au–Pd interactions in the bimetallic particles, which points to higher activity of Au@Pd or AuPd@Pd nanostructures on ceria–zirconia supports.

The hydroisomerization of n-decane over Pd/SAPO-11 bifunctional catalysts: The effects of templates on characteristics and catalytic performances

Two series of pure SAPO-11 silicoaluminophosphates (S11-B(x) and S11-P(x)) with different SiO2/Al2O3 molar ratios are synthesized by employing Di-n-butylamine (DBA) and Di-n-propylamine (DPA) templates, respectively. The effects of templates on the physicochemical properties of SAPO-11 samples are investigated by XRD, N2-adsorption, SEM, XRF, 29Si MAS NMR and Py-IR measurements. The results demonstrate that S11-B(x) samples reveal different morphology and lower strong Brønsted acid density compared with S11-P(x) samples. In addition, the linear correlation between detected and calculated total Brønsted acid densities of all samples is established. The Pd/S11-B(x) and Pd/S11-P(x) bifunctional catalysts are prepared by depositing 0.5 wt% Pd on SAPO-11 samples via the incipient wetness impregnation and hydrogen reduction methods and the n-decane hydroisomerization over all catalysts are tested. The catalytic results suggest that, due to the larger CPd/CH+ ratios and fewer strong Brønsted acid sites, Pd/S11-B(x) catalysts show higher yield of i-decanes compared with Pd/S11-P(x) catalysts, while the Pd/S11-B(0.4) shows the highest i-decanes yield of 76.75% among all catalysts. The results of long-term tests of 120 h suggest that Pd/S11-B(0.4) catalyst also has better stability because of slighter aggregation of Pd metal particles and fewer blockages of micropore openings.

Aerobic oxidation of alkyl chain in alkylphenols over combination of Pt and Pd catalysts

Oxidation of benzylic position in alkylphenols with molecular oxygen in acidic conditions, which is very difficult because of the intense dimerization or polymerization, was investigated with various combinations of noble metal catalysts. The combination of Pt/C and Pd(CH3COO)2 catalysts showed activity in the formation of p-hydroxybenzaldehyde formation from p-cresol. The best p-hydroxybenzaldehyde yield was 35%, which was obtained in 50 wt% aqueous acetic acid, Pt on carbon : Pd(CH3COO)2 weight ratio = 1 : 2, at 353 K. From XRD, TEM-EDX and XAFS characterizations, the Pt and Pd species were totally reduced to Pt and Pd metal particles, respectively, in spite of the oxidative reaction conditions. Polymerized products (“tar”) of p-cresol formed with Pt/C catalyst and air can be the reductants for Pd(CH3COO)2 into Pd metal. The catalysts or catalyst combinations without Pd metal showed no activity in the formation of p-hydroxybenzaldehyde, suggesting that Pd° is the active species. The effects of the air pressure and presence of radical scavenger were very small, suggesting that non-free-radical mechanism was involved.

Improvement Effect of Ni to Pd-Ni/SBA-15 Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A series of Pd-Ni bimetallic catalysts supported on SBA-15 (0.2%Pd-x%Ni/SBA-15, x = 0.4, 0.7, and 1.2) were prepared through the impregnation method combined with the NaBH4 reduction method. X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoemission spectroscopy (XPS) and transmission electron microscope (TEM) were used to characterize the prepared catalysts. All the synthesized catalysts were evaluated for the liquid-phase hydrogenation of cinnamaldehyde (CAL). The addition of Ni obviously enhanced the CAL conversion and selectivity of C=C hydrogenation to hydrocinnamaldehyde (HALD) over the 0.2%Pd-x%Ni/SBA-15 catalysts. Meanwhile, 0.2%Pd-1.2%Ni/SBA-15 showed the best performance with 96.3% conversion and 87.8% selectivity toward HALD. This improvement was attributed to the synergistic effect between the Pd and Ni nanoparticles, enhancing the dispersion of Pd metal particles and increasing the content of surface Pd0 species. In addition, the influences of a few reaction factors including H2 pressure, reaction temperature, and reaction time were studied over 0.2%Pd-1.2%Ni/SBA-15.

Comparing the Reaction Rates of Plasmonic (Gold) and Non-Plasmonic (Palladium) Metal Particles in Photocatalytic Hydrogen Production

Both Pd and Au metal particles are used in photocatalytic hydrogen generation. Yet while both act as electron sink only gold is poised to respond to visible light due to its plasmonic response. In order to quantitatively gauge their relative contribution into the reaction, the photocatalytic H2 production, from Au/TiO2 and Pd/TiO2 catalysts was studied under UV and UV–Vis light. While under UV light excitation, a weak dependence on the work function of the metal is observed, under UV–Vis light, Au is found to be twice more active than Pd. Under identical UV–Vis light irradiation, the turn over frequency calculated from XPS at.% is found to be 2.8 and 1.8 s−1 for Au and Pd, respectively. The effect is far more pronounced when the rates are normalized to the number of particles of each metal. Both the semiconductor TiO2 (UV light) and the plasmonic metal (visible light) need to be excited for the enhancement to occur; visible light alone causes a negligible reaction rate. Photocurrent measurements further confirmed the difference in the photocatalytic activity under UV and UV–Vis light excitation. Moreover, because of the presence of Au particles responding to visible light the reaction rate is enhanced due to “light penetration depth” effect.Graphical

Synthesis and study of nanostructured Ce-Zr-La-RE-O (RE = Y, Nd and Pr) quaternary solid solutions and their supported three-way catalysts

In this work, a series of nanostructured Ce-Zr-La-RE-O (RE=Y, Nd and Pr) quaternary solid solutions (CZLY, CZLN and CZLP) were synthesized via simultaneous co-precipitation with the assistance of lauric acid. The corresponding supported Pd-only three-way catalysts (Pd/CZLY, Pd/CZLN and Pd/CZLP) were also prepared by wet-impregnation method. The effects of Y, Nd and Pr on CeO2-ZrO2-La2O3-RE2O3 system and corresponding supported Pd-only three-way catalysts were investigated by X-ray diffraction (XRD), Raman, hydrogen-temperature programmed reduction (H2-TPR), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) characterizations. The results show that all the fresh samples form single phase structure, however, after being thermal aged at 1000°C, CZLN-a exhibits the best thermal stability which presents a remarkably low reduction peak temperature of 395°C and a high surface area of 42.6m2/g. The study of the interactions between Pd metal particles and supports indicates that Pd could selectively adsorb onto the surface Ce sites of different supporting materials by forming different chemical bonds. Pd/CZLN also exhibits superior three-way catalytic activity with respect to others, particularly, the light-off temperatures (T50) of C3H8, CO and NO for Pd/CZLN-a are as low as 339, 175 and 198°C, respectively.

Localized Surface Plasmon Resonance Assisted Photothermal Catalysis of CO and Toluene Oxidation over Pd–CeO2 Catalyst under Visible Light Irradiation

The extinction peak of Pd particles generally locates at the ultraviolet light region, suggesting that only 4% of solar light can be absorbed. Furthermore, the efficiency of LSPR hot electrons converted to chemical energy of reaction is very low due to the fast relaxation of carriers. It is extremely valuable to design Pd-based catalysts which have strong response to the visible light irradiation and high efficiency in photon to chemical energy. The Pd–CeO2 catalyst was synthesized via the hexadecyltrimethylammonium bromide (CTAB) assisted liquid-phase reduction method to generate more active interfaces. The significant extinction of Pd–CeO2 in the visible to near-infrared region indicates the strong electron interaction between Pd and CeO2. LSPR hot electrons, transferring from the Pd metal particles to the conduction band of ceria, promote the dissociation of adsorbed oxygen. Therefore, the reaction temperature of CO and toluene oxidation can be significantly lowered by visible light irradiation. The ma...

Effect of metal particles on the rate of Si etching with N-fluoropyridinium salts

The effect of Cr, Mn, Fe, Ni, Cu, Zn, Pd, Ag, Pt, or Au metal particles on the rate of Si etching using N-fluoropyridinium salts was examined. The average etching depth increased when N-fluoropyridinium salts were mixed with Cu particles. The activation energy determined from the temperature dependence of the average etching rate for the Cu particles is lower than that without a metal. The Cu particles greatly improve the etching of Si with the salts compared with the other metals. The magnitude of the effect of the Cu particles on the rate of Si etching with the salts is larger than that of the Mn, Fe, Ni, or Zn particles. This can be explained by the order of the relative stabilities of the complexes formed by bivalent ions of transition metals. The etching method involves the application of easy-to-handle salts containing Cu particles as etchants on the Si surface and has the potential to be a simple and less expensive form of Si etching.

Reduction process of Pd-containing La-Fe perovskite-type oxides by in-situ Dispersive X-ray absorption spectroscopy

Reduction process of Pd-containing La-Fe perovskites was investigated by in-situ Pd K-edge dispersive X-ray absorption fine structure as well as mass spectroscopy. The prepared perovskite was characterized by a conventional X-ray absorption spectra to confirm the incorporation of cationic Pd into perovskite matrix. Under the reductive atmosphere (5 vol%H2/He), we found the presence of three reduction processes of Pd cations in perovskite structure. The segregation of Pd metal particles was observed from 200-400 oC although the cationic Pd species remained at 700 oC due to the strong metal-support interaction.

Enantioselective hydrogenation of α-phenylcinnamic acids over cinchonidine-modified Pd/C commercial catalysts

Enantioselective hydrogenation of α-phenylcinnamic acid (PCA) and p,p′-dimethoxyphenylcinnamic acid (DMPCA) was studied over a variety of commercial 5 % Pd/C catalysts to reveal catalyst properties suitable for obtaining high enantioselectivity. The catalysts were characterized by CO adsorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). It is confirmed that pretreatment at 353 K under atmospheric pressure of H2 before modification with cinchonidine is very effective for all the Pd/C catalysts used here to improve the selectivity and reaction rate. It is suggested that the distribution of Pd metal particles is crucial to attain high selectivity (ee% = 79 ± 1 for PCA, 89 ± 2 for DMPCA): a uniform or eggshell-type distribution of Pd is more suitable than an egg-white or egg-yolk-type distribution. It is also suggested that the dispersion of Pd metal particles controls the enantioselectivity over cinchonidine (CD)-modified Pd/C catalysts. XPS techniques are proposed to provide a convenient method to find desirable catalysts. The choice of such Pd/C catalysts could facilitate high-throughput guided study on highly enantioselective hydrogenation of α,β-unsaturated carboxylic acids.

Surface chemistry and reactivity of Pd/BaCeO3∙2ZrO2 catalyst upon sulphur hydrothermal treatment for the total oxidation of methane

Starting from metal nitrates and glycine, 2% Pd/BaCeO3∙2ZrO2 catalyst was prepared by solution combustion synthesis and tested towards the total oxidation of methane. The catalyst underwent heavy sulphur-hydrothermal treatment at 800°C up to 450h. The catalyst was fully characterized (XRD, BET, SEM, O2-TPD, FTIR analyses and catalytic activity via CH4-TPC) every 150h. With ageing, catalytic activity tests demonstrated that the catalyst was heavily poisoned after 150h; then it recovered the catalytic activity after 300h, with a resulting performance better than the one reached in the fresh status. At the end of the sulphur-hydrothermal treatment, after 450h, the catalyst resulted heavily poisoned again. On the fresh catalyst surface, IR analysis of CO adsorption evidenced the formation of highly dispersed Pd metal clusters and Pd ions. After 300h of sulphur hydrothermal ageing, the increased catalytic activity towards methane combustion was probably supported by the segregation of ZrO2 and CeO2. Moreover, subsurface and bulk sulphate formation was detected with ageing and Pd metal species were not anymore available for CO coordination, probably because hindered by sulphate deposits. Prevailing ageing mechanisms resulted in the oxidation of the surface Pd metal particles and surface-bulk sulphates formation, the latter destroying the starting crystallographic structure, leading thus to the final catalytic activity decay.