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Though Metal Organic Frameworks (MOF's) and MOF-derived solids have been employed in various applications, especially catalysis, there is still a constant search for better performing MOF-based hybrid catalysts. In this work, we employed sacrificial template method in synthesizing MIL-53(Al) type - porous Alumina (MA) composites that exhibit different physico-chemical and catalytic properties compared to parent solids (MIL-53 and mesoporous Al2O3). Structural investigations demonstrated that composites possess combined structure of both the parent solids. Novel composites possess hierarchical (meso- & micro-) pores, with average pore width in the range of ~14–16 nm. NH3 adsorption calorimetry and isopropanol test enabled deducing the possible nature and strength of acid-basic sites in composites. ‘MA’ composites show intermediate chemical properties and synergistic multifunctional catalytic behaviour compared to parent solids. This work reveals, for the first time, extensively tunable physico-chemical properties of a novel class of solids: “the MIL-53(Al) type - porous alumina composites” that can have a huge potential as multifunctional catalysts.

A commercial activated carbon (AC) was characterized by physicochemical methods. The AC adsorption/desorption properties and the adsorbent regenerability were evaluated for the removal of octamethylcyclotetrasiloxane (D4), a common siloxane impurity in biogases. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) was employed to investigate the adsorption of D4 on AC at room temperature and its thermodesorption up to 300 °C. The AC was activated in N2 at varying temperatures within the 25–300 °C interval. The striking feature is the polymerization of D4 observed during the desorption experiment followed by the release of PolyDimethylSiloxane (PDMS) in the gas phase. The thermal treatment before adsorption is proposed to influence the D4–AC interaction.

The influence of the B type cation from the ABO3 perovskite formulation La0.75Sr0.25XO3 (LSX, where X is Fe, Mn or Cr) on the C and H2S tolerance and its catalytic activity for the methane/water reaction has been studied. The samples were prepared by a simple and cost-efficient citrate method. The exhaustive characterization of the bulk and surface properties of the catalysts has been accomplished by means of complementary methods: nitrogen adsorption–desorption isotherm measurements, XRD, TPR and XPS. Their catalytic properties in CH4/H2O reactions (CH4/H2O molar ratios of 10 and 1) were studied in the presence and absence of H2S in order to evaluate their potential use as anode materials in solid oxide fuel cells operated on natural gas. Before addition and upon suppression of H2S, the activity varied in the following order: LSF > LSM ≫ LSC. This correlates with the oxygen mobility determined by TPR. A strong promoting effect of H2S on the catalytic activity is observed for LSC, which makes this sample the most active of the series, while H2S has a weak influence on the other perovskites. The oxygen vacancies and the presence of S2− were identified as being responsible for the enhanced catalytic activity upon H2S addition.

Two commercial activated carbons, namely STIX and AP4, were selected to investigate their ability for siloxane adsorption and further thermal regeneration in relation with their different physico-chemical properties. In the frame of biogas purification, the studied siloxanes were L2, L3, L4 (linear molecules) and D4, D5 (cyclic molecules). The maximum capacity of adsorption was estimated by gas chromatography and gravimetric methods. AP4 presents better adsorptive properties comparing with STIX irrespective of the type of siloxane. Thermal regeneration after siloxanes adsorption was followed up to 400 °C by both gas chromatography and in situ DRIFTS. Except L2, the siloxane polymerization proceeds on the AC containing alkali metals (K, Na) as revealed by the observed release of their decomposition products during the thermodesorption treatment. The same sites are responsible for the cleavage of Si O bonds in linear molecules and formation of L2 as primary product above 100 °C. The presence of such sites, possibly strong basic sites, is detrimental to the regenerability of the spent adsorbent and to the adsorption which could be limited by partial blockage of the AC porosity. Interestingly the regenerability of the alkali-free AC depends only on the volatility of the siloxane.

SSCI-VIDE+ATARI+PGE; International audience; Stoichiometric and sub-stoichiometric lanthanum barium titanates (LBT) of perovskite structure type, substituted or not with Mn and/or Ce at the Ti-site, were prepared by sol–gel route with heat treatment in air. All the compounds display a cubic Pm-3m symmetry, which remains stable in reducing atmosphere. Whereas Mn substitution highly promotes the reducibility of the material, the electrical and electrochemical performance of Mn-doped compounds is decreased with respect to non-doped sub-stoichiometric LBT. In contrast, the electrical conductivity and resistance polarization of Ce-substituted LBT are close to those of non-doped LBT and Ce-substituted LBT appears especially efficient in improving the catalytic properties for methane steam reforming and avoiding carbon formation.

The reactivity of methane on pure- and doped (Gd, Pr)-ceria catalysts has been investigated under highly deficient steam conditions (CH 4 /H 2 O = 10) at 750 °C. The physico-chemical properties of the prepared samples were studied by XRD, adsorption-desorption isotherms of N 2 at −196 °C, and temperature programmed reduction in H 2 . The doping process led to an increase in the surface area and changes in the surface properties. Thus, doping by Pr enhanced the redox and, consequently, the catalytic properties while doping by Gd improved the catalysts stability against deactivation processes.

This work reports on the study of steam reforming of methane under water deficient conditions over Ir/Ce0.9Gd0.1O2-x (Ir/CGO) catalyst with very low Ir loading (0.1 wt% Ir). The catalyst surface was studied before and after testing by X-ray photoelectron spectrometry (XPS) and aberration-corrected high-resolution transmission electron microscopy (HRTEM) with 1 A best resolution. Ir/CGO was pretreated at 1173 K in He flow with less than 0.5 ppm O2 prior to catalytic testing. This led to the formation of Ir metal nanoparticles (NPs) with narrow-size distribution (2.5–6 nm, mean size of 4 nm in diameter). Ir/CGO slowly activated during reaction until reaching a steady state with tenfold increase of CH4 conversion rate. The initial catalytic activity was consistent with surface metal sites being the main active sites and the CGO support having no effect on the CH4 conversion rate except the inhibiting influence on the thermodynamically favoured carbon accumulation. After completion of the activation during reaction, Ir was present in the form of metallic NPs with smaller mean size (ca. 1.7 nm) than before testing, and oxidized Ir in 3+/4 + states. Metal support interactions were thought to be responsible for Ir oxidation and redispersion at the CGO surface during reaction. It is proposed that the improved catalytic activity is due to a synergy between highly dispersed Ir species and the CGO substrate through delocalization of the catalytic reactions in the vicinity of the Ir metal particles.

Ceria materials doped by Gd and/or Pr were prepared by a precipitation route and calcined in air at 500 and 900 °C. The effects of doping and thermal treatment on the materials' surfaces were studied by X-ray photoelectron and Raman spectroscopies. The redox properties were investigated using temperature-programmed reduction experiments in H2 and CH4 followed by temperature-programmed oxidation in O2. The catalytic properties of these materials in CH4/H2O reaction in the absence/presence of H2S were evaluated at 750 °C in a large excess of CH4 with respect to H2O. The materials were classified by order of reactivity as follows: CPO > CGPO > CeO2 > CGO, which can be primarily related to the surface area variation. Comparing the activity per m2 of various samples indicates that the catalytic activity is correlated with the Ce3+ concentration at the surface as measured by XPS. Gd-doped and undoped samples exhibit the highest surface Ce3+ concentration as well as the highest activity in SMR per m2, while Pr-doped samples are the least active (activity per m2) with the lowest surface Ce3+ concentrations. H2S has a sharp promoting effect on the catalytic behavior of ceria-based materials, improving the production of H2 by almost one order of magnitude.

SSCI-VIDE+ATARI+KGR:PGE; International audience; Methane appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems because it can be directly converted into hydrogen by Internal Reforming within the SOFC anode. To cope with carbon formation, a new SOFC cell configuration combining a catalyst layer with a classical anode was developed. The rate of the CH4 consumption in the catalyst layer (Ir-CGO) was determined experimentally for small values of steam to carbon ratios. This paper proposes a modelling and a simulation, using the CFD-Ace software package, of the behaviour of a SOFC operated in Gradual Internal Reforming (GIR) conditions. This model of SOFC takes into account the kinetics of the steam reforming reaction in the catalyst layer in order to assess the influence of the steam to carbon ratio and the cell polarization. Because the risk of carbon formation is greater under GIR operation, a detailed thermodynamic analysis was carried out. Thermodynamic equilibrium calculations allowed us to predict the conditions of carbon formation occurrence.

International audience

ENERGIE+PGE; An electrolyte supported solid oxide fuel cell (SOFC) was continuously operated with hydrogen, methane, and bioethanol for nearly 400 hours without adding water, O-2, or CO2, and delivering a rather stable power output. Such a fuel-flexible SOFC was achieved by using both an anodic catalytic layer, which efficiently converts the primary fuel into hydrogen, and by the operation in gradual internal reforming conditions, which prevented degradation due to carbon formation. (C) 2014 The Electrochemical Society. All rights reserved.

Electrolyte-supported single fuel cells based on yttria-stabilized zirconia components with a ceria-based catalytic layer added to the anode were operated with three different fuels: hydrogen, methane, and ethanol. Methane and ethanol were directly fed to the fuel cells without water or any oxidizing agent. Fuels were interchanged during continuous polarization and fuel cell accumulated ~160 hours of operation delivering comparable current densities for each fuel. Such result was supported by stability curves, impedance spectroscopy, and energy-dispersive X-ray spectroscopy analyses, which showed that deleterious carbon deposits are absent in the anode of tested fuel cells.

ENERGIE+AKD:SBA:BBE:PGE; A sol-gel route to synthesize nanocrystalline praseodymium-, samarium- and gadolinium-doped ceria powders for solid oxides fuel Cells SOFCs is presented. The method involves metal nitrates with propionic acid (both as chelating ligand and solvent), gel formation, liquid nitrogen quenching, drying at 150 A degrees C/24 h, and finally decomposition at 450 A degrees C in nitrogen followed by calcination at 650 A degrees C in air. TG-DTA, BET, XRD, FTIR, UV-vis and catalytic tests were used to characterize the samples. Ce0.8Pr0.2O2-delta sample exhibited the best catalytic performance in methane steam reforming under water deficient conditions, closely followed by Ce0.9Gd0.1O2-delta, Ce0.8Sm0.2O2-delta and Ce0.8Gd0.2O2-delta catalysts. The superior catalytic performance of Ce0.8Pr0.2O2-delta sample was attributed to the existence of praseodymium species (Pr4+/Pr3+) strongly interacting with ceria. The two systems act synergistically in the catalytic steam reforming of methane.

The CO oxidation reaction on carbon-supported Pt nanoparticles (average size of 2.8 to 7.7 nm) was studied under flowing conditions at atmospheric pressure and temperatures between 300 and 353 K by coupling quadrupole mass spectrometry (QMS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The Pt loading was varied between 20 and 60 wt%. Gases diluted in He (0.5 mol%) were used together with Ar as a tracer. Reactions with CO and O2 introduced separately onto the samples were studied by QMS, applying successive step changes of the reaction mixtures. Variations in the rate of the reactions were observed and correlated with changes of the calculated coverage of the Pt surface by CO and/or O adspecies at varying steps of the experiment. The transient reaction of CO(g) with adsorbed O (Oad) was fast and mass transport-limited while that of O2(g) with adsorbed CO (COad) was sluggish. Following the same experimental procedures, FTIR spectra of adsorbed CO after varying steps were recorded, confirming the variations of COad and Oad as determined by QMS and indicating changes in the CO distribution over varying types of Pt surface sites. The influence of the adlayer composition (co-adsorption of COad and Oad), the particle size/structure and some possible surface reconstruction effects on the CO oxidation rate were evidenced and discussed. The structure of the Pt nanoparticles supported on carbon appears as an important factor for the efficiency of the so-called O2 bleeding as a CO mitigation strategy in polymer electrolyte membrane fuel cells.

Electrolyte (yttria-stabilised zirconia, YSZ) supported solid oxide fuel cells (SOFCs) were fabricated using spin coating of standard LSM cathode and Ni-YSZ cermet anode. A ceria-based catalytic layer was deposited onto the anode with a special current collector design. Such a single cell configuration allows operation by gradual internal reforming of direct carbon-containing fuels. First, the fabricated single cells were operated with hydrogen to determine the optimised conditions of fuel concentration and flow rate regarding faradaic efficiency. Then, the fuel was switched to dry ethanol and the cells were operated for several hours (100 h) with good stability. Post-operation electron microcopy analyses revealed no carbon formation in the anode layer. The results indicate that the gradual internal reforming mechanism is effective, opening up the way to multi-fuel SOFCs, provided that a suitable catalyst layer and cell design are available.

6 Perillat-Merceroz, Cedric Gauthier, Gilles Roussel, Pascal Huve, Marielle Gelin, Patrick Vannier, Rose-Noelle; The possibility to introduce cerium in the perovskite-type titanate with formula La0.33Sr0.67TiO3+delta (LST) was investigated. Pure-phased La0.23Ce0.1Sr0.67TiO3+delta (LCST) was only obtained by synthesis at high temperature in reducing (diluted hydrogen) atmosphere. The material exhibits the same orthorhombic symmetry with Immm space group as LST and nearly the same cell volume. When exposed to oxidizing atmosphere at 1200 degrees C, Ti3+ and Ce3+ oxidation leads to the decomposition of LCST and the growth of several nanoscaled Ce-rich phases, as highlighted by backscattered electron microscopy. Shifting the gas back to a reducing atmosphere, but at lower temperature, only involves partial reversibility, ensuring the presence of nanoparticles of (electro)catalytically active phase within an electronically conducting n-type network. The catalytic tests in methane steam reforming at 900 degrees C (CH4/H2O = 10/1) show that the properties of the partially decomposed phase are greatly improved, what could make it a promising anode material for SOFC operating on slightly wet methane.

In this paper, based on a multiscale modelling framework, we focus on understanding the impact of CO adsorption on the intrinsic stability properties of PtxCoy nanoparticles under PEMFC anode operating conditions. First, CO adsorption effect on PtxCoy has been studied by using Monte Carlo (MC) simulation. Then, the MC results are coupled with an ab initio based kinetic model to simulate the effect of CO poisoning on the activity and durability of the PtxCoy nanoparticles as HOR catalysts. The results are compared with simulations carried out with pure Pt, where potential self-oscillatory behaviour is detected and experimentally confirmed. The PtxCoy HOR activity and stability reveals to be strongly dependent on the nanoparticle size and composition. For some nanoparticle sizes, simulations show that PtCo nanoparticles provide better CO tolerance than Pt3Co. CO adsorption on PtCo slows down Co dissolution in short-term operation. However, this effect is overcome by the increase of the anode potential due to CO adsorption. Thus, CO adsorption enhances Co dissolution in long-term operation. Due to this Co dissolution, the HOR activity of PtCo degrades faster than Pt3Co in long-term operation.

Mosqueda, Bertha Toyir, Jamil Kaddouri, Akim Gelin, Patrick; The catalytic properties of gadolinium-doped ceria (CGO) in methane steam reforming were studied. Catalytic tests were carried out between 750 and 900 degrees C, for H2O/CH4 ratios varying between 0.1 and 1, pretreated in H2O/N-2, N-2 and H-2/N-2. Above 800 degrees C, slight deactivation with time on stream was observed except for the H-2-pretreated sample. Surface area measurements, O-2 adsorption at room temperature and O-2-temperature programmed oxidation experiments were performed after catalytic testing. Changes in both surface area and redox properties of CGO were observed and related to catalytic deactivation. Hydrogen is thought to play a key role in catalytic activity and deactivation process. (C) 2008 Elsevier B.V. All rights reserved.

SSCI-VIDE+ATARI+GPO:PGE; International audience; Cerium oxide powder catalyst was prepared by microwave-assisted hydrothermal synthesis, characterized by physicochemical techniques andtested in catalytic dry reforming of methane in view of a potential useas anode material of Solid Oxide Fuel Cells operated on biogas. Theconventional hydrothermal method was also used for comparison toevaluate the benefits of the non conventional preparation route.Microstructure and reduction-reoxidation properties of samples preparedby both routes were studied by XRD, adsorption-desorption isotherms ofN-2 at -196 degrees C, Raman spectroscopy and temperature programmedreduction in H-2. Repeated cycles consisting of temperature programmedreduction in CH4 (TPR-CH4) followed by temperature programmed oxidationin O-2 (TPO) were also performed. The catalytic properties of CeO2samples were investigated in dry reforming of methane between 750 and900 degrees C under stoichiometric (0.5% CH4 and 0.5% CO2 in He carrier)and oxidizing (0.25% CH4-0.75% CO2 in He) conditions. The preparationunder microwave irradiation allows: i) obtaining crystallites withsmaller size, ii) enhancing the stability towards redox treatments, iii)improving the surface and bulk reducibility by H-2 and CH4, iv)favoring the creation of defects. These improved properties correlatewell with better catalytic performances in dry reforming of methane withrespect to the conventionally prepared ceria sample. Copyright (C)2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. Allrights reserved.

A study on the synthesis of La 1− x Ag x MnO 3+ δ ( x = 0, 0.2) using a microwave process (MWhyd) has been carried out by comparing the heating time and reaction temperature with the same factor under conventional thermal process (CHhyd). Experiments have been conducted using the hydrothermal method at medium pressure ( T = 200 °C, P = 20 atm) followed by a thermal treatment of the precursor at 700 °C (10 h). Structural and physico-chemical properties of the catalysts were investigated using X-ray diffraction (XRD), BET sorption, temperature-programmed reduction or desorption, mass spectrometry (TPR-MS and TPD-MS), and X-ray photoelectron spectroscopy (XPS). While CHhyd and MWhyd powder catalysts exhibited the same XRD patterns indexed as pure perovskite structure, their surface physico-chemical properties were found to be strongly influenced by the preparation method. The effect of the nature of oxygen species, their amount and mobility, evidenced by temperature programmed experiments, on the catalytic properties in methane combustion in the presence and in the absence of hydrogen sulphide has been studied. MWhyd-La 0.8 Ag 0.2 MnO 3+ δ catalysts were found to exhibit a much better performance in methane combustion together with higher resistance to sulphur poisoning than CHhyd catalysts.

International audience; A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO3–(14%) La2CrO6 or 94%LaCrO3–6%La2O3 were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m2 g−1. Highly crystalline, pure phase of LaCrO3 and La2CrO6 powders were also prepared, with BET area of 4 and 3 m2 g−1, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O2-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO3, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO3 and La2O3 samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO3 exhibited significant catalytic activity which was sensitively affected by the modifier La2CrO6 or La2O3.

We report here on the activity and stability of LaMnO3.15 for the methane combustion, in the absence and presence of H2S, in a temperature interval of 250–750 °C. Two powders with different specific surface area were prepared by coprecipitation method using ammonia. Precursors calcined at high temperature, in air, for 10 h have led to LaMn-C solid with SBET = 11 m2/g, while those previously aged in solution (hydrothermal treatment at 200 °C under 20 atm. for 24 h) then calcined at high temperature led to LaMn-HydC with SBET = 31 m2/g. Temperature programmed reduction (TPR) profile of both samples showed two main peaks; surface and weakly bound oxygen named α-oxygen species and lattice oxygen β-oxygen species. While for LaMn-C the maximum reduction temperature peak corresponding to α-oxygen species was found to be ca. 600 °C, for LaMn-HydC samples this peak was shifted to lower temperature ca. 430 °C. Indeed, LaMn-HydC samples showed higher depletion of surface and weakly bound oxygen species compared to LaMn-C. The superior catalytic performance of LaMn-HydC in methane combustion was attributed to its high BET surface area and to both the high amount of α-oxygen species and their mobility. In the presence of 100 ppm H2S in the feed this catalyst showed a higher propensity to poisoning by sulphur compounds than LaMn-C. This was attributed to the rapid formation of stable sulphate/sulphite species, the decomposition of which occurs above 800 °C.

International audience; Bimetallic Pd–Pt catalysts with constant 2 wt% metal loading and varying Pt/Pd ratios were prepared, characterized and studied in the catalytic combustion of methane at low temperature under lean conditions in view of their use for CH4 abatement from lean-burn NGV heavy duty vehicles exhausts. The influence of mild steam ageing featuring long-term use of the catalysts was also addressed together with their tolerance to H2S. Catalysts were characterised by Transmission Electron Microscopy and Temperature Programmed Oxidation experiments. Experimental data agreed to suggest an interaction between Pd and Pt in Pdrich catalysts, thus explaining their improved catalytic activity, even after mild ageing, compared to reference Pd/Al2O3. This interaction has no effect on the sulfur tolerance.

International audience; The preparation of binary materials based on Ta2O5-ZrO2 by a sol-gel method and with a wide range of compositions is reported (Ta2O5 nominal content from 4 to 74% w/w). Materials were characterized by X-ray diffraction, and infrared and Raman spectroscopy. Their acidic characteristics were evaluated from the model reaction of 2-propanol dehydration and the adsorption of CO at 77 K and 2,6-dimethylpyridine at 373 K, both followed by infrared spectroscopy. Increasing tantalum content brings about a development of a surface TaOx phase followed by a progressive formation of aggregates of amorphous Ta2O5. Increased stabilization of tetragonal zirconia was also observed with increasing Ta loading. The surface area, number and strength of Bro¨nsted acid sites, and the catalytic activity in the 2-propanol dehydration increase with the increase in tantalum content up to ca. 50% w/w Ta2O5. A surface area of 103 m2 g-1 was obtained for a solid with a Ta2O5 content of 53% w/w after calcination at 873 K. The abundance of Bro¨nsted acid sites, determined by lutidine adsorption, and their strength, determined by CO adsorption at 77 K, correlated with the catalytic activity in the 2-propanol dehydration.

Well crystallised aluminium borate Al 18 B 4 O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2 /g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18 B 4 O 33 was prepared by conventional impregnation of Pd(NO 3 ) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18 B 4 O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2 O 3 . Pd/Al 18 B 4 O 33 exhibited a much lower activity than Pd/Al 2 O 3 when treated in hydrogen at 500 °C or aged in O 2 /H 2 O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18 B 4 O 33 which became as active as Pd/Al 2 O 3 . Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2 O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18 B 4 O 33 . The existence of two distinct types of PdO species formed on Al 18 B 4 O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2 .

The catalytic combustion of methane at low temperature under lean conditions was investigated over bimetallic palladium-platinum catalysts supported on alumina. Pd-Pt catalysts with constant 2 wt.% metal loading and varying compositions in Pt and Pd were prepared by successive impregnations of the metal salts. The catalysts were characterised by powder X-ray diffraction, transmission electron microscopy/electron dispersion X-ray spectroscopy (TEM/EDX), volumetry of H2 chemisorption, FTIR study of CO adsorption and temperature-programmed oxidation (TPO). In the absence of water added to the feed, the methane conversion over Pd-rich bimetallic catalysts (Pt/Pt + Pd molar ratios less than 0.3) was found to be the same as that of the reference Pd/Al2O3 catalyst. Interestingly, under wet conditions, these bimetallic catalysts exhibited an improved performance with respect to Pd/Al2O3. This effect was found to be maintained upon mild steam ageing. An interaction between both metals was suggested to explain the enhanced activity of bimetallic catalysts. This was confirmed by TPO experiments indicating that formation and decomposition of PdO is affected upon Pt addition even for very low amounts of Pt. The adsorption of CO on reduced catalysts studied by FTIR revealed new types of adsorbed CO species, suggesting again an interaction between two metals.

A series of Pd/Al 2 O 3 catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H 2 PdCl 4 , Pd(NO 3 ) 2 and Pd(AcAc) 2 ) and pre-treatments. The mean particle size of reduced samples was determined by H 2 chemisorption. The catalytic activity in methane oxidation under lean burn conditions was measured. The oxidation of reduced samples was studied at 300 °C. The extent of oxidation was found to decrease with increasing mean particle size. While small particles ( 15 nm) proceeded via a two-step process, being first fast and then slow. The decomposition of oxide species was studied by temperature-programmed experiments under vacuum. Two distinct oxidised species with different stability were evidenced depending on the particle size. Oxidised species in larger particles were found of lower stability than in smaller ones. A correlation between the existence of distinct types of oxide species and catalytic properties in methane oxidation was discussed.

A commercial NOx-storage catalyst for gasoline applications containing platinum, palladium and rhodium together with Ba/CeO2/Al2O3 has been sulfated on the engine bench at 390 and 510 °C with nominal exposures of 0.3 and 1.3 g sulphur/l catalyst. Exposures of 0.3 g/l are too low to have a notable impact on the catalytic performance. At 390 °C, the sulphur is quantitatively adsorbed as opposed to 510 °C. Sulphur is mainly adsorbed at the inlet side of the catalyst thereby shielding the downstream region. Desulfation on synthetic gas bench at 700 °C leads to a removal of 50% of the sulphur. The residual sulphur is more evenly distributed along the length of the catalyst compared to the sulphur profile in the sulfated catalyst. This leads to an improvement of the NOx-activity at the inlet side and a drop in NOx-performance at the outlet side after desulfation. Results from SEM–EDX, TPD, TPR and IR suggest that the barium component is selectively poisoned by the sulphur while alumina and ceria are not affected significantly. The insufficient desulfation of the catalyst is almost entirely due to the incomplete sulphur removal from the barium sites. In the desulfated state the IR and TPD-data suggest the presence of barium carbonate species of low thermal stability together with bulk carbonate. After sulfation the IR data indicate the presence of different sulphate species, both bulk and surface phases. Thermal ageing and sulphur poisoning affect different parts of the operational temperature window of the NOx-storage catalyst. While thermal stress alone mainly affects low temperature NOx-performance, sulphur poisoning mainly reduces high temperature activity. The results of this work help to identify strategies to improve both the sulfur resistance of the catalyst and the operational conditions for a better management of the NOx-trap system.

The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H2S (100 vol. ppm). Their catalytic properties were compared to those of Pd/Al2O3 and Pt/Al2O3. In the absence of H2S in the feed, Pt/SnO2 appears as a very promising catalyst for CH4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al2O3. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO2 is slightly less resistant than Pd/Al2O3. In the presence of H2S, Pt/SnO2 catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3, and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2 sites active in CH4 oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2.

The selective catalytic reduction (SCR) of nitric oxide by propene under lean-burn conditions over Ir/Al 2 O 3 and Ir/SiO 2 was studied. Irrespective of the support, Ir supported catalysts were found to be active in the reduction of NO above 673 K, Ir/SiO 2 being the most active. For both catalysts, the activity in the reduction of NO into N 2 was shown to be strongly enhanced after their exposure at 873 K under the reaction mixture. In spite of varying initial Ir dispersions depending on the metal content and the support, Ir sintered after activation in the reaction mixture, which led to the same final Ir dispersion. An in situ FTIR study of both catalysts at various temperatures under the reaction mixture and under CO or NO used separately was carried out. It was shown that, under the reaction mixture, the surface of initially fully oxidised Ir particles progressively reduced with increasing temperatures into partially reduced Ir δ + surface species allowing the adsorption of both CO and NO ( ν CO at 2070–2050 cm −1 and ν NO at 1870 cm −1 ). Additional species (formate, acetate, nitrate) formed only on the Al 2 O 3 support surface but these species are thought not to participate into the NO reduction.

The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH 4 traces under lean-burn conditions was studied in the presence or the absence of water or H 2 S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H 2 S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H 2 S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H 2 S-poisoned Pd/Al 2 O 3 catalyst was studied by TPD in O 2 /He. Poisoning species decompose above 873 K as SO 2 and O 2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O 2 /He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H 2 S-poisoned Pd/Al 2 O 3 . A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested.

The interactions of CO with a high specific surface area tin dioxide was investigated by FTIR spectroscopy and thermogravimetric analysis. FTIR study of CO interactions have shown that CO can adsorb on cus (coordinatively unsaturated sites) Sn4+ cation sites (band at 2201 cm-1). In addition, CO reacts with surface oxygen atoms. This leads to the partial reduction of SnO2 surface and to the formation of ionised oxygen vacancies together with the release of free electrons, which are responsible for the loss of transmission. Formed CO2 can chemisorb on specific surface sites: on basic sites to form carbonates species and on acidic sites (Sn4+-CO2 species) which is in competition with the formation of Sn4+-CO species. TG experiment have shown that the reduction of SnO2 by CO at 400°C occurs in two steps. First, the reduction of SnO2 surface, which is a quick phenomenon. This has allowed to evaluate that more than 12% of reducible surface oxygens can react with CO, essentially because of the presence of a large amount of surface hydroxyl groups. The second step of the reduction of SnO2 would be the progressive reduction of SnO2 bulk by the slow diffusion of oxygen atoms from the bulk to the surface.

SSCI-VIDE+ATARI+PGE; International audience; Pure and 5% Mn doped layered perovskites La4SrTi5O17, members of the La4Srn-4(Ti,Mn)(n)O3n+2 series with n = 5, have been synthesized and investigated as anode materials for Solid Oxide Fuel Cells. The use of XRD, neutron and electron diffraction techniques allows clarifying some divergences concerning the structural characterization within the family, not only in air but also in anodic-like N-2/H-2(97/3) atmosphere. The electrical conductivity of both compounds is very low in air but those values increase by two orders of magnitude in diluted hydrogen. The study of catalytic properties for methane steam reforming as well as in-depth analysis of the SOFC anodic behaviour of both materials are described, for which a microstructure optimization of the electrode allows to demonstrate the potential interest of the lamellar materials upon the classical three-dimensional cubic-like LSTs. (C) 2014 Elsevier B.V. All rights reserved.

MICROSCOPIE:XPS+ATARI:ECI2D+GPO:MAO:PGE:LCS:LPI; International audience; This study reports on the investigations performed on an Ir-CeO2 (0.1 wt% Ir) catalyst, prepared for the first time by one-step solution combustion synthesis (SCS) and submitted to a number of analyses: N-2 volumetry, elemental analysis, X-ray diffraction, scanning electron microscopy, aberration-corrected high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed methods. The catalyst was studied in the steam reforming of methane (SRM) at 750 degrees C, under water-deficient conditions (CH4/H2O ratio of 10) and in the presence of 220 ppm H2S. The obtained catalytic performances were compared with those of an Ir/CeO2 catalyst prepared by incipient wetness impregnation (IWI). The influence of the support and the metal was investigated through testing of Ir/SiO2-Al2O3-IWI and Rh-CeO2-SCS catalysts, respectively. Using CeO2 as carrier, Ir-based catalysts are highly efficient in SRM and resistant to carbon and irreversible sulfur poisoning. The catalytic activity of Ir-CeO2-SCS is superior to that of Ir/CeO2-IWI. Unlike the Ir-CeO2 catalyst, Ir/SiO2-Al2O3 is completely deactivated in presence of sulfur, while Rh-CeO2-SCS does not recover its initial activity after exposure to an H2S-containing feed. (C) 2014 Elsevier B.V. All rights reserved.

SSCI-VIDE+ATARI+GPO:PGE; International audience; Cerium oxide catalysts for fuel cells application were synthesized via precipitation and modified precipitation routes where the effect of H2O2 and/or cetyltrimethylammonium bromide (CTAB) addition in the precipitation step has been investigated. Microstructure and reduction-reoxidation properties of the oxides were analyzed by XRD, adsorption-desorption isotherms of N-2 at -196 degrees C, TG-DTA, Raman, SEM, TPR-H-2, TPR-CH4 and TPO. The catalytic properties of CeO2 samples were investigated in dry reforming of methane (DRM) between 750 and 900 degrees C under both stoichiometric (CH4 and CO2 in equal amounts) and oxidizing (excess of CO2 with respect to CH4) conditions. A material exploitable for applications in catalysis and solid oxide fuel cells (SOFCs) was obtained by modifying the precipitation route via the addition of H2O2 (CeO2_H2O2). Compared to materials synthesized conventionally or by using CTAB, CeO2_H2O2 exhibited the best thermal stability, least surface loss under high temperatures operation (e.g. 900 degrees C), superior stability with respect to bulk redox properties when alternating between oxidizing and reducing treatments,,and highest catalytic activity and resistance to deposition of graphitic carbon. (C) 2015 Elsevier B.V. All rights reserved.

This review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature. The abatement of natural gas vehicle (NGV) methane emissions is taken as one example among possible applications. The review develops current ideas about the properties of palladium and platinum catalysts supported on silica and alumina supports in the complete oxidation of methane under oxidising conditions, focusing on low-temperature reaction conditions. The influence of residual chloride ions on the catalytic activity, the kinetic aspects of the oxidation of methane over these catalysts, the nature of the active sites, the influence of metal particle size and reaction products on the activity, the observed changes in catalytic activity with reaction time and the effect of sulphur containing compounds are examined. The latest studies concerned with improved palladium and platinum supported catalysts which would exhibit enhanced and stable catalytic activity at low temperature in the presence of water and sulphur containing compounds are reported. Possible routes for preparing catalysts able to meet future regulations concerning methane emissions from lean-burn NGV vehicles are discussed.

The selective catalytic reduction (SCR) of nitric oxide by propene over Ir/Al 2 O 3 under lean-burn conditions (1000 vpm NO, 2000 vpm C 3 H 6 , 500 vpm CO, 10 vol.% O 2 ) was studied. The activity was shown to be strongly enhanced after exposure of the catalyst at 600°C under the reaction mixture, irrespective of the oxidising or reducing pre-treatment. Simultaneously, the Ir dispersion decreased from 78 to 10%. The influence of each component of the reaction mixture on the activation process was examined. The presence of both CO and O 2 was found to be necessary to activate Ir/Al 2 O 3 while NO would not be. In situ FT-IR results revealed that initially fully oxidised Ir particles partially reduced in the feed to form Ir 0 reduced surface sites ( ν CO at 2060 cm −1 ) which adsorbed CO up to 350–400°C. The activation under reactants was related to the formation of these sites. The presence of reduced (or partially reduced) Ir sites, possibly siting at the surface of IrO 2 particles and stabilised by CO adsorption, was proposed to be responsible for the SCR activity.

The surface composition of alumina-supported Pd, Rh, and Pd–Rh catalysts fresh or after high temperature treatments under oxidizing (O2 in N2) or reducing (H2 in N2) mixture has been characterized using various complementary techniques: chemisorption and titration of H2 and O2 probe molecules, 18O2/16O2 isotopic equilibration (OIE), FTIR spectroscopy of adsorbed CO and NO, and electron microscopy with X analysis. From both techniques it is concluded that the surface composition is close to the bulk composition for all the fresh bimetallics, whatever the Rh content. The surface state of the bimetallics treated at 1173 K is strongly dependent on the nature of the gas mixture. There is a relative increase in surface Pd after treatment in an oxidative medium, because of a Rh3+ migration into alumina, and in surface Rh after treatment in a reducing medium. The specific role of alumina can explain these results, in contradiction with thermodynamic models predicting the reverse situation (enrichment in Rh in O2 and in Pd in H2). Activity for propane oxidation at 573 K and for propane steam reforming at 673 K was also determined over fresh and sintered catalysts. Because Pd is more active than Rh in oxidation and Rh is more active than Pd in steam reforming, activity changes with the Rh content, before and after sintering, may reflect modifications of surface composition. The results obtained with the series of Pd–Rh catalysts are in agreement with the measurements made by OIE and FTIR spectroscopy. The hypothesis and the conditions of applications of the methods are discussed.

Pd and Pt catalysts supported on alumina, tin(IV) oxide and tin(IV) oxide grafted on alumina were prepared, characterised and tested with respect to the low-temperature combustion of methane after reduction in H2 and ageing under reactants at 600°C. In the case of Pd, the use of SnO2 or SnO2-based supports led to catalysts slightly less active than Pd/Al2O3. In contrast, SnO2 was found to strongly promote the oxidation of methane over Pt catalysts with respect to Pt/Al2O3, even after ageing under reactants. When Pt was supported on SnO2 grafted on Al2O3, the activity was found at most similar to or, after ageing, lower than Pt/Al2O3. This negative effect was discussed, being partly related to the sintering of SnO2 under reactants observed by FTIR and XRD.

The adsorption of NO on Pd-exchanged H-ZSM-5 containing from 0.18 up to 1.56 wt.% Pd was studied by in situ FTIR spectroscopy and dynamic volumetric experiments. At room temperature, NO adsorbs as two distinct NO-containing species (ν(NO) at 2136 and 1881 cm−1). These species exhibit different thermal stability: the 2136 cm−1 species easily decomposes in acuo below 473 K while the 1881 cm−1 species is stable up to 673 K. At 523 K in flowing NO, only the 1881 cm−1 species forms and NO2 is released. The striking feature is that the release of NO2 is delayed with respect to the NO consumption and that, after being formed, NO2 is reversibly adsorbed with NO in a 1:1 ratio inside the channels of the zeolite. By combining mass spectrometry, IR spectroscopy and volumetric data, the transient species were unambiguously associated with the 2136 cm−1 species and attributed to NO+ occupying exchange sites. All these data were consistent with the reduction of Pd(II) into Pd(I) ions dispersed in the zeolite channels and the subsequent formation of Pd(I) mononitrosyl complexes responsible for the 1881 cm−1 feature. The Pd(I) nitrosyl complexes are monovalent and strongly anchored to the zeolite framework, as indicated by the appearance of a sharp IR band at 975 cm−1 attributed to distorted T–O (T = Si, Al) vibrations. The dispersion of Pd as isolated complexes at exchange sites in the zeolite channels was found to depend strongly on both Pd loading and activation conditions.

Pd/Al2O3 catalysts prepared by the impregnation of alumina free of chlorine with H2PdCl4 and Pd(NO3)2 precursors were characterised and their catalytic activity in methane oxidation was measured under oxygen-rich conditions. The presence of residual chlorine ions either originating from the precursor or from impregnation with HCl was shown to strongly inhibit the conversion of methane. Residual chlorine ions could be slowly removed under reaction conditions in the form of HCl. This was observed by in situ measurement of HCl departure and catalytic activity. Experimental data were explained by a simple model in which residual chlorine would block PdO surface active sites during the reaction. The resulting catalyst, free of chlorine ions, was similar to the one prepared from the nitrate precursor in terms of dispersion and activity. Chlorine-free catalysts exhibited slow deactivation with time on stream, which was tentatively attributed to the slow conversion of the active PdO phase into a less active Pd(OH)2 phase. This interpretation was supported by the poisoning effect of water vapour observed upon addition of water to the feed while CO2 had no influence. Regeneration of the catalyst could be achieved by purging in dry carrier above 500°C, which could be ascribed to the decomposition of Pd(OH)2 into PdO.

International audience; SnO2-based sensors present strong interactions with NOx-containing atmospheres. For this reason, it is fundamental to identify the nature of the adsorbed species resulting from the interaction of NO and NO2 with the tin oxide surface. This aspect has been studied in literature by Temperature Programmed Desorption (TPD). To state more precisely structures of adsorbed species, we link TPD with Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). Concerning NO2 adsorption, DRIFTS experiments indicate the formation of monodentate nitrato species at room temperature. By increasing the temperature, a conversion of adsorbed species is observed. The nature of surface groups is discussed. In the presence of hydroxyl groups (two different OH groups are evidenced), the formation of hydrogeno nitrates is detected.

The influence of various hydrothermal treatments on the physicochemical properties of pure H-mordenites and matrix-embedded H-mordenites was investigated. It was found that the crystallinity and the chemical composition of pure mordenite were strongly dependent on the ageing conditions. Embedding of mordenite had no influence on the extent of dealumination and prevented the mordenite structure from collapsing. This protecting effect of the matrix on the zeolite structure was not observed for a physical mixture MOR/matrix, thus suggesting that intimate contact between the zeolite and the matrix is necessary for such an effect to take place. This intimate contact MOR/matrix was confirmed by the formation of new chemical bonds between hydroxyl groups on the outer surfaces of the zeolite crystals and those on the surface of the embedding matrix.

SSCI-VIDE+ATARI:CARE+CDS:PGE; International audience; Pd was introduced by exchange in non-dealuminated and dealuminated mordenites. After activation under oxygen at 500 degrees C, NO adsorption revealed the presence of isolated Pd2+ ions and Pd/PdO particles. Two types of Pd ions were shown: the first one would be located in the small cavities and leads to the formation of dinitrosyl complexes, whereas the second one, probably sitting in the main channels, is responsible for the obtainment of mononitrosyl complexes. Pd/PdO particles are active in the direct combustion of CH4 by oxygen and poorly active in the selective reduction (SCR) of NO. Pd ions are active for the NO SCR; the ions in the main channels are thought to be more active than the ions in the small cavities for accessibility reasons. In the case of the non-dealuminated mordenite catalyst, an activation under reactants is observed. Moreover, the activity is increased by the addition of 10 vol% water which is the opposite of the classical behavior of metal-loaded zeolites. Both phenomena are attributed to a migration of Pd ions from hidden to accessible sites. For the dealuminated sample, the observed deactivation seems to be due to a migration of isolated Pd ions into PdO particles located outside the zeolite matrix. (C) 1998 Academic Press.

ENERGIE:MATERIAUX:SURFACES+GPO:FBS:GBR:NSP:PGE; In order to understand the exceptional tolerance of ceria to high sulfur levels in the fuel for further SOFC applications, the interaction of sulfur with a commercial Ce0.9Gd0.1O2-x (CGO, from Praxair) and its influence on H-2 production from CH4/H2O mixture was studied. The activity tests were performed at 750 C, in the presence of H2S and under gradual internal reforming conditions (large excess of CH4 with respect to water vapor, 10:1). The presence of H2S in the reactant mixture promoted the catalytic activity of CGO. The nature of various species formed by sulfur-ceria interaction is discussed based on CH4-TPR, XRD, XPS, and in situ FTIR results. H2S reacts with ceria fraction in CGO and generates new catalytic sites with improved reactivity toward CH4. The formation and stabilization of oxygen vacancies by S-insertion in ceria lattice are evidenced and directly related to the improved activity. The detrimental effect of Ce2O2S phase, when formed, on the catalytic activity of doped ceria is confirmed. (C) 2014 Elsevier Inc. All rights reserved.

MICROSCOPIE:RX:XPS+ATARI:ECI2D:ING+GPO:SLO:FBS:LBU:MAO:LMA:PGE:FMO:LPI; International audience; Mesoporous ceria loaded with 0.06-0.93 wt% iridium was synthesized in one step by the ambient air combustion of an aqueous solution of ceric ammonium nitrate, ammonium hexachloroiridate, and glycine fuel. The structural properties of the powders, and the influence of such parameters as Ir loading and thermochemical post-treatments, were investigated combining aberration-corrected HRTEM, SEM, in situ XRD, XPS, DRIFTS, and Raman spectroscopy. The materials, which appeared spongy at the micrometer scale, exhibited ca. 30 nm-sized ceria crystallites with a layered structure at the nanoscale. After reducing treatments, Ir nanoparticles anchored at the surface of ceria grains were identified, and their size (ca. 2 nm) did not evolve upon further heating at up to 900 degrees C. A detailed picture of the Ir-CeO2 interface could be established, with the presence of Irx(+)-O2--Ce3+ entities along with oxygen vacancies. The powders loaded with only 0.1 wt% Ir were successfully employed as catalysts for the production of hydrogen from methane and water in low-steam conditions at 750 degrees C. Due to their higher Ir dispersion and stronger Ir-CeO2 interaction, the combustion-synthesized materials outperformed their conventionally prepared counterparts in terms of activity and stability, making them promising as active catalytic layers for solid-oxide fuel cells integrating the gradual internal reforming concept.

SSCI-VIDE+ATARI:CARE+CDS:PGE; International audience; Pd-exchanged MFI-type zeolites containing 3.7 and 0.7 framework aluminium atoms per unit cell (corresponding to Si/Al ratios of 25 and 131) were found active in the selective reduction of nitrogen monoxide in the presence of excess oxygen. Upon steaming at 800 degrees C, both catalysts exhibited the total loss of their catalytic activity in the reduction of NO. Such a behaviour was ascribed to the complete aggregation of Pd ions into large metal particles on the external surface of the zeolite crystals. Both supports, although maintaining their crystallinity, are shown to experience extended dealumination upon steaming. Although the loss of Pd exchange capacity could partially explain the Pd migration and sintering, a mechanism involving the formation of mobile Pd hydroxyl entities condensing into PdO particles outside the zeolite crystallites is preferred. (C) 1997 Elsevier Science B.V.

In a previous paper the preparation and the characterization of PtNaY and PtInNaY were reported. Here, complementary characterization results obtained by studying the TPD of CO by mass spectrometry coupled with IR studies of the adsorbed CO phases indicated no apparent change in the electronic properties of Pt. Comparison of catalytic properties for n -butane hydrogenolysis between PtNaY and PtInNaY indicated that the hydrogenolysis is deeply affected by the addition of In to Pt; the kinetic parameters (apparent activation energy, relative order for butane and for hydrogen) are modified by In addition. These results are explained considering that In is acting more like a diluent of Pt atoms than as an electronic modifier of Pt.

The formation of pyridinium ions upon pyridine sorption on HY samples of varying Al composition has been studied by IR spectroscopy. It is demonstrated that HY supercages cannot accommodate more than four pyridinium ions. This property is shown to affect the ability of LF protons to migrate towards positions accessible to pyridine and form pyridinium ions. The mode of interaction of LF hydroxyls with pyridine is discussed in the light of both steric and electrostatic parameters.

ENERGIE+KIC:VBE:PGE; CO adsorption on carbon-supported Pt nano-particles under operando conditions was studied by quadru-pole mass spectrometry and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). The Pt catalyst was also studied by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). It was shown by HRTEM and XPS that Pt nanoparticles can be fully reduced by H-2 at room temperature instead of by conventional high-temperature treatment. The Pt dispersion was determined by XRD, HRTEM, and CO chemisorption techniques with an excellent agreement among them. The room-temperature H-2/O-2 titration method was also used, but if assuming H/Pt-s = O/Pt-s = 1, it led to the underestimation of the dispersion compared to the other techniques. The existence of adsorption sites inaccessible to H-2 (or O-2) but accessible to CO because of a stronger interaction with Pt was proposed to explain the results. It was also concluded that H/Pt-s was lower than unity (H/Pt-s = 0.72) and, as a major consequence, that Pt nanoparticles with 2.7 nm diameter still have a bulk-like behavior in contrast with what was reported in the literature for 1 nm Pt particles. CO adsorption on Pt/C at 298 K after H-2 treatment was studied by operando DRIFTS. The C-O stretching vibration (nu CO) bands were ascribed to CO adsorbed on Pt surface at (111)-terrace, (100)-terrace, edge, and kink sites in linear and bridge forms. An unexpected nu CO band at 1703 cm(-1) was observed upon CO adsorption and tentatively attributed to CO on surface Pt sites interacting through its oxygen end with the carbon support. It was also shown that the adsorption of CO and H-2 in successive repeated steps was necessary to reach a stable state of the adsorbed CO phase. Possible reconstruction of Pt nanoparticles at room temperature during this process is discussed.