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The structural evolution of two Pt/ceria–zirconia catalysts, characterized by different amounts of supported Pt, was monitored by in situ X-ray diffraction during the anaerobic oxidation of CO at different temperatures. In a first phase, oxygen coming from the surface layers of the ceria–zirconia mixed oxide is consumed and no structural variation of the support is observed. After this induction time, bulk reduction of Pt/ceria–zirconia takes place as a step-like process, while the CO2 production continues at a nearly constant rate. This behavior is totally different from that of the metal-free support in similar reaction conditions, that show a gradual bulk reduction. In repeated oxidation–reduction cycles, it was observed that the induction time in Pt/ceria–zirconia is a function of the thermal history, of the amount of supported Pt and of the structural evolution of the samples. r 2003 Elsevier Inc. All rights reserved.

Liotta, L. F. Ousmane, M. Di Carlo, G. Pantaleo, G. Deganello, G. Marci, G. Retailleau, L. Giroir-Fendler, A.; Co3O4, CeO2 and Co3O4-CeO2 mixed oxides with Co/Ce nominal atomic ratio 0.1:5, prepared by co-precipitation method with sodium carbonate, were tested in the oxidation of propene under lean condition and the catalyst stability was checked by performing three consecutive heating-cooling cycles. Characterization of the textural properties were performed by surface area measurement BET, X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. Among the Co3O4-CeO2 mixed oxides, Co3O4 (30 Wt%)-CeO2 (70 wt%) gives the best activity attaining full propene conversion at 250 degrees C. This sample is characterized by the presence of Co3O4 particles well dispersed and in good contact with ceria according to BET and XRD data and as evidenced by SEM micrographs. Oxygen temperature-programmed desorption (O-2-TPD) and C3H6-temperature-programmed reduction (C3H6-TPR) experiments were carried out in order to study the surface and bulk oxygen mobility and to correlate it to the activity. At temperature around 200 degrees C, O-2-TPD experiments showed the desorption of mobile surface oxygen species for the most active samples, Co3O4 and Co3O4 (30 wt%)-CeO2 (70 wt%). C3H6-TPR experiments for both of the oxides also evidenced a high reactivity at low temperature, especially, for Co3O4 (30 wt%)-CeO2 (70 wt%) giving at 345 degrees C an intense peak of CO2 formation. Conversely, the ceria sample showed by C3H6-TPR much less pronounced oxygen bulk mobility, starting to react with propene above 500 degrees C and forming only CO. In this case, the catalytic activity of ceria was explained in terms of formation of surface oxygen vacancies which are relevant to the propene oxidation in presence of gaseous oxygen. (c) 2008 Elsevier B.V. All rights reserved.

Palladium and gold–palladium catalysts supported on mesoporous silica were prepared by incipient wetness impregnation. They were characterized by XPS, XRD, BET, and FTIR acidity measurements. The activity was tested in the oxidation of methane under lean conditions. The effect of adding SO 2 to the reactant mixture was investigated. Test reactions were consecutively performed to evaluate the thermal stability and poisoning reversibility. The palladium catalyst performed quite well in terms of the light-off temperature ( T 50 300 °C) and SO 2 tolerance. Moreover, the activity, which decreased after a night treatment in SO 2 at 350 °C, was completely recovered in subsequent cycles. The presence of gold decreased the activity slightly without altering the SO 2 tolerance. Evidence of a dynamic reduction–oxidation process occurring at the palladium surface was obtained from the gold-promoted sample in which the reduction of palladium on SO 2 treatment was ascertained.

A catalyst with 0.7 wt% Pd load supported over Co3O4 oxide was investigated in the methane oxidation by operating under CH4/O2 stoichiometric conditions. The effect of the noble metal addition on the activity of bare Co3O4 was evaluated. Samples were characterized by BET, XRD, TPR and XPS analyses. The SO2 poisoning of Pd catalyst and Co3O4 was studied by performing CH4 oxidation tests under stoichiometric conditions in SO2 (1 ppm or 10 ppm). Experiments evidenced that in our conditions the low amount of SO2 doesn’t influence the Pd behaviour, whereas in presence of 10 ppm of SO2 some deactivation occurs that becomes more evident above 450 °C at which the catalyst doesn’t reach 100% of methane conversion. Catalytic tests performed over Co3O4 and the Pd supported catalyst, after a treatment at 350 °C for 15 h in 10 ppm SO2/He, suggest that Co3O4 is a sulphating support, as confirmed by XPS analysis. Therefore, an important role in lowering the sulphur poisoning of Pd may be played by Co3O4.

Co3O4/CeO2 and Co3O4/CeO2–ZrO2 composite catalysts have been prepared by two different techniques, co-precipitation by citrate method and impregnation with cobalt nitrate of pre-formed ceria and ceria–zirconia oxides. The materials, as prepared and after ageing at 750 °C 7 h, were tested for methane combustion and the catalytic performances were compared with those of a commercial Co3O4, used as reference. A significant improvement of the activity was observed in the composite oxide Co3O4(30 wt%)/CeO2(70 wt%), prepared by citrate method, which exhibits the lowest light-off temperature of methane (T50 = 400 °C) and does not suffer deactivation after calcination at 750 °C 7 h.

Temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) have been used to study the various cobalt species formed in a cobalt catalyst (Co 1 wt.%) supported on alumina-baria, with composition Al2O3(80 wt.%)–BaO (20 wt.%). The catalyst was synthesized by incipient-wetness impregnation of the support with a water solution of cobalt acetylacetonate and calcined at 550 °C for 5 h. In order to investigate the structure and morphology of the sample, XRD, BET and SEM analyses were performed. Depending on the temperature and nature of pre-treatment (reductive or oxidative) different Co species (Co3O4, Co3+, surface Co2+, CoAl2O4) were formed. Activity tests in the reduction of NO by CO were carried out in order to investigate the effectiveness of the catalyst depending on the redox pre-treatment. Highly dispersed Co3O4 particles, formed after a TPR up to 1100 °C and successive TPO up to 550 °C are active for the NO reduction at low temperature, N2O being the major product at 250 °C, while N2 formation was favored at temperature higher than 400 °C. The as prepared sample, calcined at 550 °C for 5 h, exhibits significant activity only at temperature > 400 °C, giving selective formation of N2. The nature of the active species in the supported catalyst was confirmed by studying the CO + NO reaction and NO decomposition over Co3O4 and CoO oxides as reference materials. On Co3O4 the NO reduction occurs with different selectivity to N2O/N2, depending on the reaction temperature: at low temperature only N2O was detected, whereas at temperature >350 °C also N2 formation was observed. Then at temperature ≥450 °C only the reaction NO→N2 takes place. Over CoO the reaction starts at ∼400 °C and N2 is the only nitrogen product detected in the whole range of temperature investigated. Hundred percent of NO conversion into N2 is reached at 600 °C.

The structural properties and the hydrodesulfurization (HDS) activity of sodium doped and sodium free CoMo catalysts supported on amorphous aluminosilicates (ASA) were investigated as a function of different SiO2:Al2O3 ratios. The support yielding the most active catalyst, (66% alumina) doped with different amounts of sodium, was used for a series of similar catalysts in order to study the effect of the alkali ion on the catalytic performance. The supports were prepared by sol–gel method and the catalysts were prepared by incipient wet impregnation method. The structure and the surface of the various samples were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic behaviour was tested in the hydrodesulfurization of thiophene carried out in a continuous flow system at atmospheric pressure, in a range of temperature between 603 and 633 K. Changes of activity with the support composition were observed. The presence of sodium, modifying the Bronsted acidity of the supports, enhances such effect. Moreover, the increase of the activity with increasing amount of sodium was a clear indication of the promoting effect of the alkali ion.

Silver–palladium bimetallic catalysts were supported on pumice following different procedures, based on mild treatments of organometallic precursors. The experiments for the structural characterization of the synthesized samples, wide angle X-ray diffraction (XRD) and X-ray absorption spectroscopy, were carried out at the beamline GILDA of the European Synchrotron Radiation Facility. The analysis of the data demonstrated that alloying took place with a degree of homogeneity depending on the different preparation routes.

The reaction of [(eta(5)-C7H7)Fe(CO)(3)](-) with [(eta(4)-C8H12)(eta(5)-C5H5)Pt](+) leads to the formation of syn-[(mu-eta(3);eta(2)-C7H7)Fe(CO)(3)Pt(eta(2),sigma(1)-C8H12-H-12-C5H5)] (1), a bridged cycloheptatrienyl complex with an Fe-Pt bond. In solution two structural isomers of 1 are present in roughly the same concentration, whereas in the solid only one isomer is detected. Both isomers are fluxional and undergo ring whizzing of the C7H7 ring. The slow-exchange limiting NMR spectrum of the cycloheptatrienyl unit cannot be reached even at low temperature (similar to 173 K). The C7H7 ring has an uncoordinated double bond and the cyclopentadienyl unit is linked to the C8H12 ring through an sp2 carbon; the resulting cyclooctenyl unit is coordinated eta(2),sigma(1) to platinum. The C5H5 transfer, mediated by platinum, can be of interest in the synthesis of the skeleton of natural occurring products. Crystal data for syn-[(mu-eta(3);eta(2)-C7H7)Fe(CO)(3)Pt(eta(2),sigma(1)-C8H12-C5H5)]: monoclinic, space group C2/c (No.15), a=45.197(6),b=13.306(1), c=7.509(1) Angstrom, beta=92.95(1)degrees, V=4509.8(9) Angstrom(3), Z=8 R=0.033, R(w)=0.080.

Ceria nanosized oxides with high surface area were synthesized by means of a templating approach, using a porous silica xerogel with surface area as high as 718 m2/g. After impregnation of the silica template with the cerium salt solution and further calcination at 600 °C, the final ceria oxide was recovered by dissolving the silica framework in NaOH solution. The effect of cerium counteranion, nitrate or chloride, on the textural and reduction properties of the ceria oxide was examined. Characterizations by BET and pore size distribution, XRD, TPR and SEM/EDX techniques were performed. The silica xerogel templated approach resulted in the preparation of ceria with surface area of 205 m2/g and very small particle size (∼5 nm), when cerium chloride precursor was used. An enhanced reducibility, at temperature

Four series of cobalt-based catalysts, such as bare Co3O4 and CoO, CoOx-CeO2 mixed oxides, CoOx supported over alumina and alumina-baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV-visible diffuse reflectance spectroscopy and TG/DT were performed. The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al2O3-BaO and CoMgAl. The samples Co(1 wt%)/Al2O3-BaO and Co(1 and 3 wt%)/Al2O3 show a comparable medium activity, while the oxidation properties of bare oxides Co3O4, CoO and CoOx-CeO2 are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina-baria look much more stable. The recycle of CoOx/Al2O3 and CoOx/Al2O3-BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated. On the basis of TPR and UV-visible results it appears that highly dispersed Co2+ ions especially present over Co(3 wt%)/Al2O3-BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone.

Two structured composite oxides, Co3O4(30wt%)-CeO2(70wt%), have been prepared by washcoating commercial cordierite monoliths with a CeO2-γAl2O3 layer, on which the active phase Co3O4-CeO2 was added through two different methods: dip-coating from a suspension containing the preformed active oxide or impregnation with a solution of the cobalt and cerium precursors. Morphological characterizations of the monoliths have been performed by BET, and SEM-EDAX analyses. Electronic and reduction properties have been evaluated by XPS and H2-TPR, respectively. The effect of the preparation method has been investigated in the catalytic oxidation of CO, whereas the promotion by a low content of Pd-Pt has been evaluated in combined CO-CH4 oxidation tests. Four successive CO oxidation cycles performed over the structured Co3O4-CeO2 indicate that the best performing sample is the monolith prepared by dip-coating, whereas that one obtained by impregnation method manifests a certain deactivation upon two consecutive cycles. Accordingly, XPS spectra are consistent with the presence of the active phase CO3O4 in the former, while Co2+ has been identified as the main species in the latter sample.

Several compositions of palladium-loaded calcium hydroxyapatite Pd(x)/CaHAp were prepared and characterized by XRD, IR, and UV–visible spectroscopy and temperature-programmed reduction (TPR). The acid–base properties of the samples were studied with the use of butan-2-ol conversion and IR spectroscopy coupled with lutidine adsorption/desorption. Calcium hydroxyapatite bears Lewis acid sites of moderate strength and a limited number of Bronsted acid sites, which produce butenes by dehydration. The selectivity of the dehydrogenation reaction (formation of methyl ethyl ketone) is very limited in the absence of oxygen but indicates the existence on the surface of phosphate of basic sites that are as essential as the acid sites in the direct synthesis of methyl isobutyl ketone (MIBK) from acetone and H2. Dispersion of Pd on the hydroxyapatite introduces redox properties and the bifunctionality needed in the hydrogenation of mesityl oxide (MO). Temperature-programmed reduction (TPR) of Pd(x)/CaHAp catalysts shows a sharp peak of H2 consumption between 268 and 276 K, depending on palladium loading, followed by a negative peak at about 338 K, which is associated with the decomposition of β-PdH. Hydrogen chemisorption measurements carried out at 353 K allowed the determination of the size of palladium particles, which varies between 8 and 28 nm. The Pd(x)/CaHAp catalysts showed good performance in the low-pressure one-step synthesis of MIBK. They are stable under the experimental conditions, and they exhibit a MIBK and MIBC selectivity that reaches 92% for a conversion of 22% and an optimal Pd loading of 2 wt%. Other parameters of the reaction (such as temperature of reaction, residence time, H2/acetone ratio) were studied. They all play an important role in acetone conversion and product distribution. However, the reaction temperature has the most significant influence, since a maximum of the global conversion was observed at 423 K.

Chromium oxide samples supported over silica and zirconia were prepared by wet impregnation of the supports with aqueous solution of CrO3. In order to investigate the influence of the preparation method on the chromium dispersion and oxidation state, one sample was prepared by sol-gel technique. The materials were structurally characterized by XRD analysis. The oxidation states of chromium species were investigated by XPS, DRS and TPR/TPO techniques. EPR analyses were also carried out for the sample Cr/SiO2, that due to the low crystalline state exhibits broad XPS signals. In this case, particular attention was paid to the presence of Cr(V) and Cr (III) species and their concentration. The oxidizing performances of the chromia supported reagents have been evaluated for the liquid phase oxidation of benzyl alcohol to benzaldeyde, in absence of molecular oxygen. With the aim to investigate the redox behaviour of anchored Cr and to evaluate the amount of regenerable Cr species (upon TPR/TPO process), oxidation tests were carried out on fresh and aged samples (i.e. after 7 redox cycles up to 600degreesC). A correlation was found between the benzyl alcohol conversion and the amount of chromium reduced by TPR of used samples (i.e. after 22 h of reaction). (C) 2004 Elsevier B.V. All rights reserved.

The steady-state activity of NO reduction by C3H6, in lean conditions, was studied on a Pt(1%)/Ce0.6Zr0.4O2 catalyst, in a plug-flow reactor, in the temperature range 100–500 °C. The influence of reductive pre-treatments on the catalytic performance at low temperature (250 °C) was investigated. Enhancement of the activity was found for the catalyst pre-treated in hydrogen at 350 °C as compared to the sample pre-treated in H2 at 800 and 1050 °C. Moreover, transient reactivity tests of NO reduction by hydrogen were also carried out. As previously observed, the sample reduced at 350 °C was the most active catalyst. In both types of reactions the temperature and the nature of pre-treatments had no effect on the selectivity to N2 at the temperature of maximum NO conversion. Analyses by temperature programmed reduction (TPR), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) supported the occurrence of a strong metal–support interaction (SMSI) effect between platinum and ceria and the important role of the platinum in promoting the ceria-zirconia structural reorganization. Such type of interaction determined a decrease of the platinum and ceria reduction temperature and a stabilization of the platinum oxide even in reducing atmosphere at high temperature. The catalytic behavior of the Pt/ceria-zirconia catalyst was discussed in terms of the structural and electronic modifications induced by the SMSI effect.

Two Al 2 O 3 (24 wt%)–La 2 O 3 (76 wt%) supported Co–La oxides with Co loading 4 wt% and different La content (1 and 9 wt%) were prepared by co-impregnation of the support, the aluminum–lanthanum oxide, with cobalt and lanthanum nitrates in aqueous solution and successive calcination at 800 °C for 4 h. The alumina–lanthana was synthesized by the sol–gel method. The samples were characterized by X-ray diffraction (XRD) and Rietveld refinement in order to identify the crystalline phases and their relative weight. H 2 -TPR (Temperature Programmed Reduction) experiments were recorded with the aim to identify the different Co phases present. Co 3 O 4 and LaCoO 3 were formed for La loading of 1%, whereas at higher La loading (9%) LaCoO 3 and La 2 O 3 oxide prevailed. In both catalysts LaAlO 3 phase was also detected. As observed by BET and SEM characterizations, the morphology of the two catalysts was somewhat affected by La:Co atomic ratio and differed dramatically from those of the reference bulk oxides, Co 3 O 4 and the mixed phase LaCoO 3 /La 2 O 3 . Activity tests in C 3 H 6 and CH 4 combustion were carried out in order to discriminate the catalytic properties of different phases formed (Co 3 O 4 , LaCoO 3 , La 2 O 3 , LaAlO 3 ).