The NOx storage reduction (NSR) process is commonly envisaged for the NOx treatment of exhaust gas from lean-burn engine vehicles. NOx are firstly stored on the catalyst, which is periodically submitted to a reducing mixture for few seconds in order to reduce the stored NOx into N-2. The on-board reducer is coming from the gasoline/diesel fuel and, in fact, the NSR catalyst is submitted to a mixture of hydrocarbons, CO and H-2 with various compositions depending on the lean/rich step. In this study, the influence of each reducer (C3H6, CO and H-2) is evaluated separately, with a special consideration to the N2O selectivity. It is demonstrated that the N2O can be emitted during both lean and rich periods, with varying ratio depending on the considered reducer and the temperature of gas. For instance, at 300 degrees C, a high N2O selectivity is observed when C3H6 is used, and near half of the N2O emission occurs during the storage phase in lean condition. (C) 2012 Elsevier B. V. All rights reserved.

The Selective Catalytic Reduction of NOx with ethanol (EtOH-SCR) was studied over Ag/Al2O3 catalysts. A special attention was given to the ammonia emission and its possible relationship with the support acidic properties. For this purpose, five aluminas were selected, three provided by manufacturers and two synthesized in our laboratory by sol–gel or precipitation route. The supports were impregnated with 2wt.% Ag, and tested in EtOH-SCR. The results showed that the catalytic activity of Ag/Al2O3 greatly depends on the used alumina. An unexpected ammonia production is evidenced, varying between 6 and 27% at 450°C, while NOx are fully converted. A correlation was established between the NH3 yield and the Lewis acid sites (LAS) density measured by pyridine adsorption for each catalyst.

During citral hydrogenation, the products distribution obtained on Rh/TiO2 and Pt/TiO2 catalysts depends on their preparation and activation protocols: (i) the unsaturated alcohols (the intended products) are formed in higher quantity on samples reduced at 500°C and more notably with Pt/TiO2 catalyst; (ii) samples prepared by impregnation of the metallic precursor salt in HCl medium and activated at 300°C are the only ones to lead to the formation of isopulegol as by-product. On the catalysts activated at 500°C, these results can be explained by the presence of the SMSI effect beneficial to hydrogenate selectively the CO bond of citral towards unsaturated alcohols.

Methane abatement from rich gas mixture was performed in a plasma-catalyst reactor. The inlet concentration of CH4 varied from 0.15 to 1vol.% of the total flow rate. Influences of different parameters such as temperature, gas composition and catalyst were investigated. The catalyst was an alumina wash-coated monolith made of cordierite containing 0.15wt% of palladium and 15wt% of Al2O3. The plasma was generated by means of a high voltage monopolar excitation. The higher the energy density, the higher the methane conversion. For plasma experiments carried out without catalyst, the CH4 conversion reached a maximum of 33% for 1vol.% CH4 and 49% for 0.3vol.% CH4 in a N2/O2/CO2/H2O gas mixture (75/18.7/4/2vol.%) at 200°C and 1823JL−1. Carbon monoxide (CO) was observed to be the main product. The CO yield reached 29% and 49% for 1 and 0.3vol.% CH4, respectively. Moreover, experiments performed with a hybrid plasma-catalytic reactor showed two different behaviours depending on the catalyst location. In POST-plasma position, the presence of the catalyst did not modify the methane conversion but oxidized CO into CO2. In IN-plasma position, the catalyst inhibited the methane conversion by decreasing the plasma volume between electrodes but oxidized CO into CO2.

The effect of Sn addition to Pd on the selective liquid-phase hydrogenation of citral to α,β-unsaturated alcohols (UA: nerol and geraniol) was examined. Pd–Sn/SiO2 bimetallic catalysts were prepared by successive impregnation method and were characterized by transmission electronic microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX), temperature-programmed reduction (TPR), Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS). Sn addition to Pd/SiO2 catalysts significantly modifies their properties for citral hydrogenation performed at 130°C, under 7MPa and in isopropanol solvent, inducing a promoting effect on the UA selectivity. This promoting effect is related to the existence of a Pd–Sn interaction highlighted by EDX analysis, TPR under hydrogen and FTIR of adsorbed CO. The latter technique suggested the presence of a geometric effect on catalytic activity. Maximum UA selectivities (>75% at 30% citral conversion) were obtained when an alloy of the Pd3Sn type is formed in the bimetallic particles, as confirmed by TPR and XPS. Moreover, FTIR measurements of the adsorbed CO singleton frequency as well as XPS binding energy shifts strongly imply an electron transfer from Sn to Pd, which is proposed to be responsible for enhanced adsorption of citral CO bond on the surface of Pd–Sn/SiO2 bimetallic catalysts. To our knowledge, it is the first time that modified Pd catalysts lead to such important UA selectivity values during α,β-unsaturated aldehyde hydrogenation.

A simple and efficient route to prepare supported nanocrystalline oxides is presented. The synthesis procedure, i.e. in situ autocombustion of a glycine complex, allows the production of nanocrystals in a porous matrix presenting larger pore size. An example of successful formation of 2-5 nm nanocrystals is given for a single oxide (Fe(2)O(3)), a mixed-oxide structure (LaCoO(3) perovskite-type) and a nickel-doped oxide.

Reduction of Pd° and decomposition of palladium oxide supported on γ-alumina were studied at atmospheric pressure under different atmospheres (H(2), CH(4), He) over a 4 wt% Pd/Al(2)O(3) catalyst (mean palladium particle size: 5 nm with 50% of small particles of size below 5 nm). During temperature programmed tests (reduction, decomposition and oxidation) the crystal domain behaviour of the PdO/Pd° phase was evaluated by in situ Raman spectroscopy and in situ XRD analysis. Under H(2)/N(2), the reduction of small PdO particles (<5 nm) occurs at room temperature, whereas reduction of larger particles (>5 nm) starts at 100 °C and is achieved at 150 °C. Subsequent oxidation in O(2)/N(2) leads to reoxidation of small crystal domain at ambient temperature while oxidation of large particles starts at 300 °C. Under CH(4)/N(2), the small particle reduction occurs between 240 and 250 °C while large particle reduction is fast and occurs between 280 and 290 °C. Subsequent reoxidation of the catalyst reduced in CH(4)/N(2) shows that small and large particle oxidation of Pd° starts also at 300 °C. Under He, no small particle decomposition is observed probably due to strong interactions between particles and support whereas large particle reduction occurs between 700 and 750 °C. After thermal decomposition under He, the oxidation starts at 300 °C. Thus, the reduction phenomenon (small and large crystal domain) depends on the nature of the reducing agent (H(2), CH(4), He). However, whatever the reduction or decomposition treatment or the crystal domain, Pd° oxidation starts at 300 °C and is completed only at temperatures higher than 550 °C. Under lean conditions, with or without water, the palladium consists of reduced sites of palladium (Pd°, Pd(δ+) with δ < 2 or PdO(x) with x < 1) randomly distributed on palladium particles.

In this work the effect of palladium load (1–4%, w/w) and particle size (2–6 nm) on the catalytic activity in CH4 combustion and on the reduction/reformation behaviour of PdO during alternate CH4-reducing/CH4-lean combustion pulses was investigated over Al2O3 supported catalysts. PdO-reduction/reformation cycles occurring during the tests were confirmed to be beneficial with respect to deactivation phenomena observed during prolonged exposure to lean combustion atmosphere. The results showed that the catalyst with lower Pd load and higher metal dispersion exhibits a lower specific catalytic activity in CH4 combustion, which is likely associated with a lower reducibility of smaller PdO particles as evidenced by CH4-TPR experiments. The more dispersed system also showed a slower reactivation dynamics upon exposure to lean combustion atmosphere. Such behaviour has been tentatively associated with the presence of ultradispersed species that during oxidation form poorly active aluminate complexes first, which are then slowly transformed into reducible PdO.

Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO2/SiO2 nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400°C), nanocomposites having titania nanodomains (∼2–3nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800°C does not allow to detect the anatase to rutile transition. Even at 800°C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ∼10nm, a size close to that of the silica host support porosity (8.4nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO2/SiO2 solids are promising in term of thermal stability.

TiO2/SiO2 nanocomposites are synthesized and fully characterized after thermal stabilization at temperatures between 400 degrees C and 800 degrees C. The control of the impregnation media is crucial to obtain nanocomposites of satisfactory quality, i.e. presenting no segregation of titania particles outside the silica pore structure. Characterization shows that pore size and pore volume decrease linearly with an increase in titania loading, and remain close to the theoretical values calculated assuming the formation of a non-porous coating. Surface area remains unchanged whatever the titania loading (always comprised between 450 and 480 m(2) g(-1)), and micropore volume evolution suggests the formation of nanometric particles within the silica pores. While X-ray diffraction is inefficient to identify the titania phase, Raman spectroscopy showed the formation of anatase particles, with crystal sizes in the nanometric range (<4.5 nm, when stabilized at 400 degrees C). Satisfying thermal stability is obtained on the low titania loading nanocomposites (20 wt% TiO2), with only minor anatase crystal growth up to 800 degrees C. Further characterization by FT-IR of the surface chemical properties of the nanocomposites showed properties similar to that of conventional titania, while improved oxygen mobilities (as evaluated by the O-18/O-16 exchange reaction) are reported on the low titania loading, thermally stable, composites.

Four sets of Rh-Ge/TiO2 bimetallic catalysts were prepared by surface redox reaction (i.e., catalytic reduction method) between hydrogen activated on a Rh parent catalyst and a Ge salt dissolved in aqueous solution. The four sets of catalysts differ depending on the presence or absence of chloride ions in the Rh and Ge precursor salts used (i.e., RhCl3 vs. Rh(NO3)(3), GeCl4 vs. GeO2). Samples were reduced either at a lower temperature (300 degrees C) or at a temperature chosen to induce a strong metal-support interaction (SMSI) effect (500 degrees C). Catalysts were characterized by elemental analysis, transmission electronic microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy of adsorbed CO and evaluated for their activity for the gas phase dehydrogenation of cyclohexane and selective hydrogenation of citral. Regardless of the nature of the Rh and Ge precursor salts, the catalytic reduction method causes the Ge to be in intimate contact with the Rh particles, favoring the citral hydrogenation toward unsaturated alcohols (UA: nerol and geraniol). For low Ge loadings, the bimetallic effect can be combined with the SMSI effect. It was observed that the UA selectivity is directly correlated to the ratio R (R = Sigma A(COads on oxidized Rh >= 1+ species)/Sigma A(COads on total exposed Rh species)) determined by FTIR. A better UA selectivity is obtained when bimetallic catalysts possess a surface in a predominantly oxidized state, a situation that is enhanced when chlorinated rhodium and germanium precursors are used. (C) 2010 Elsevier Inc. All rights reserved.

The deactivation and regeneration of naphtha reforming PtReGe/Al2O3 and PtReSn/Al2O3 catalysts prepared by catalytic reduction were studied. The extent and nature of coke deposition as determined by TPO were related to catalyst properties such as dispersion, acidity and Cl content. The PtReSn catalyst was the most resistant to coke deactivation.Regeneration was performed by calcination in oxygen at 450 degrees C or ozone at 125 degrees C at variable regeneration times. Regenerated catalysts were evaluated by cyclopentane hydrogenolysis, cyclohexane dehydrogenation and n-heptane reaction tests. Regeneration by oxygen burning-off was the most effective for decoking. However, oxygen combustion produced more segregation of the metal function than ozone regeneration. With the regeneration conditions used in this work, the original acidity of the catalysts cannot be recovered. (C) 2010 Elsevier B.V. All rights reserved.

Platinum based mesostructured SiO2 supported TiO2 nanoclusters (TiO2 content ranging from 10 to 50wt.%) were synthesized and characterized. Titania nanodomains (<4nm) dispersed in the silica porosity are obtained. Derived 1wt.% Pt/xTiO2-SiO2 nanocomposites were tested in the cyclohexane dehydrogenation reaction, a structure insensitive reaction to evaluate metal-support interaction. Pt/xTiO2-SiO2 nanocomposites display largely higher SMSI effect than measured over classical Pt/TiO2 P25 catalyst. While platinum particle size is found to be affected by the titania loading in the composite, similar SMSI effect is measured for all solids displaying similar TiO2 crystal size. Titania crystal size is evidenced as an important parameter allowing a control of the SMSI effect: the lower the crystal size, the stronger the metal-support interaction.

Ge was deposited by catalytic reduction on Pt-Re/Al2O3-Cl base catalysts prepared by coimpregnation. The nominal amounts of Ge incorporated from various impregnation media (H2O, HCl, or NH3) were 0.1, 0.3, 1.0, and 2.0 wt %. The catalysts were characterized by means of the test reactions of cyclohexane dehydrogenation and cyclopentane hydrogenolysis. The catalysts were further characterized by FTIR spectroscopy of adsorbed CO and adsorbed pyridine and by temperature-programmed desorption of pyridine. Blank treatments performed on the Pt-Re/Al2O3 base catalyst in the different media (without Ge addition) showed that the catalytic reduction method modified the properties of the parent catalyst depending on the pH of the solution. The Bronsted acidity decreased as the impregnation pH was increased, whereas the Lewis acidity of the catalyst was not substantially modified by any of the impregnation media. Catalysts with higher Pt-Re interactions were obtained after treatment in a solution of high pH (NH3 medium). The interaction between Ge and the active metal phase increased with increasing Ge content. This interaction resulted in a decrease of the metal activity in cyclohexane dehydrogenation and cyclopentane hydrogenolysis. Catalyst performances were evaluated in n-heptane (n-C-7) reforming under pressure. The n-C-7 tests showed that trimetallic catalysts obtained by impregnation of small quantities of Ge (<= 0.3 wt %) using a neutral aqueous solution are the most active and toluene-selective, especially compared to those prepared using HCl or NH3 solution. Nevertheless, the use of ammonia in the impregnation medium allows one to decrease the amount of cracking products. Thus, the catalytic properties might be improved by using a slightly basic medium for the impregnation of Ge.

The influence of Sn addition by catalytic reduction method on the Pt-Re/Al2O3 properties for the n-C-7 reforming reaction was studied. The Sn addition was performed in different media (HCl and H2O). It Was found that trimetallic Pt-Re-Sn/Al2O3-Cl Catalysts prepared in H2O or HCl medium present a good interaction between Sn and the catalytically active species (Pt-Re). This strong interaction of Sn with the active phase correlates with the lower hydrogenolytic and dehydrogenating activity of the trimetallic catalysts. Total acidity and Bronsted acidity decrease with the addition of Sn. The catalysts prepared in HCl have both higher Bronsted and total acidity in comparison to those prepared in H2O.In the case of catalysts prepared in HCl medium, the production of C-2-C-4 gases in the n-C-7 reforming reaction also decreases upon Sn addition confirming that the cracking activity decreases when the acidity is decreased. In both trimetallic catalysts series a decrease in the toluene yield can be seen at high Sn contents. The production of toluene depends on the activity in dehydrocyclization reaction. Dehydrocyclization requires sites of lower acid strength than those needed for cracking. The addition of small amounts of Sn (<= 0.2 wt%) would enable the step of sulfidation of Pt-Re/Al2O3 catalysts to be spared. (C) 2009 Elsevier B.V. All rights reserved.

Pt-Re-Ge/γAl2O3 catalysts were prepared by the catalytic reduction method using different impregnation media (H2O, HCl and NH3) and different Ge contents (0.0, 0.1, 0.3, 1.0 and 2.0%). The influence of these preparation parameters on the activity for n-heptane conversion and the selectivity to toluene at atmospheric pressure was assessed. The catalysts were also characterized by ICP-AES, temperature programmed reduction, pyridine temperature programmed desorption and CO pulse chemisorption. The results show that as the pH is increased the Ge content increases and the catalysts present a lower hydrogenolytic activity and a lower toluene selectivity. Ge addition modifies both metal and acid functions. The catalyst with minimum Ge content prepared using water as impregnation medium has the best performance.

Infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopy measurements were used to characterize the species formed after impregnation of Pt5Fe2(COD)(2)(CO)(12) onto silica, before and after removal of the organic ligands. The results indicate that the Pt5Fe2(COD)(2)(CO)(12) cluster adsorbs weakly on the SiO2 surface. Nevertheless, partial disintegration of the cluster was observed during aging even under He and at room temperature, related to the loss of CO ligands due to their interactions with silanol groups of the support. The organic ligands can be removed from a freshly impregnated cluster by thermal treatment in either He or H-2, but the surface species formed in each case have different structures. Treatment in He at 350 degrees C leads to a complete disintegration of the Pt-Fe bimetallic core and results in the formation of highly dispersed Pt clusters with a nuclearity of six, along with surface Fe oxide-like species. In contrast, bimetallic PtFe nanoparticles with an average size of approximately 1 nm were formed when a similar H-2 treatment was used. In this case, a greater degree of metal dispersion and a larger fraction of Pt-Fe interactions were observed compared to the PtFe/SiO2 samples prepared by co-impregnation of monometallic salt precursors. Electronic interactions between Pt and Fe atoms in such cluster-derived samples led to an increased electron density on platinum, as indicated by a red shift of the frequencies of FTIR bands for adsorbed NO and CO. These electronic interactions affect the strength of the CO adsorption on platinum. All bimetallic samples were found to be more active than Pt/SiO2 for the oxidation of CO in air; however, the activity depends strongly on the structure of the surface species, the fraction of Pt-Fe bimetallic contributions, the degree of electronic interactions between Pt and Fe, and the strength of the CO adsorption on platinum. (C) 2008 Elsevier Inc. All rights reserved.