The Rh-Ge/TiO2 and Pt-Ge/TiO2 bimetallic catalysts are prepared and characterized by Fourier transform infrared (FT-IR) spectroscopy of adsorbed CO. The catalytic reduction procedure induces modifications of the intensity of the bands, indicating thus some changes on the surface of the Rh metallic phase. FTIR investigation of adsorbed CO reveals that the intensity of each peak associated to the different CO absorbed species falls when the germanium content of the catalyst increases. These different modifications show the existence of an interaction between the germanium and rhodium on the bimetallic Rh-GeTiO2 catalysts, and germanium and the platinum on the bimetallic Pt-Ge/TiO2 catalysts.

Pt, Ir and Rh were deposited on SiO2 or Al2O3 using chlorinated precursors and various amounts of HCl in the impregnation medium. The Bronsted and Lewis acidities increased with the chlorine content of the alumina supported catalysts. The silica-supported catalysts only presented Lewis acid sites. The catalysts were evaluated in methylcyclopentane (MCP) and methylcyclohexane (MCH) ring-opening (RO) under pressure (2.85 and 3.95 MPa, respectively), from 200 to 425 degrees C. For MCP conversion, the acidity of the alumina support had no sensitive effect on the activity and selectivity to RO products, and few effects on the distribution of RO products. No isomerization or hydrocracking products were observed, confirming that these reactions occurred mainly on the metal function, which was not modified by the presence of chlorine. The nature of the support, SiO2 or Al2O3, had a strong effect on both the activity (1.9 against 0.5 mol h(-1) g(-1) (metal) for Ir/Al2O3 and Ir/SiO2, respectively at 225 degrees C) and selectivity to RO products (99.6% against 97.5% for Ir/Al2O3 and Ir/SiO2, respectively, at 80% of MCP conversion) for Ir catalysts only. Interestingly, the Rh/SiO2 exhibited a high selectivity for converting MCP to RO products, similar to Ir/Al2O3, i.e. 99.6% at 80% of conversion. Depending on the metal and the supports, three types of behavior were observed for MCH ring-opening: (i) a direct ring-opening on the metal function whatever the support for Ir, (ii) a first step of isomerization, and then a need of a sufficiently acidic support, for Pt and (iii) an intermediate behavior for Rh, which was able to either directly convert MCH in absence of acidic support or favor a bifunctional mechanism on chlorinated alumina. (C) 2013 Elsevier B.V. All rights reserved.

A series of supported Pt-Rh bimetallic systems was prepared either (i) by the refilling method (a surface redox reaction), or (ii) by the classical coimpregnation or (ii) by mechanical mixture of supported monometallic Pt and Rh catalysts and acidic support (chlorinated alumina). Two oxide supports were used for these preparations, i.e. alumina and silica. All these systems, largely characterized in a previous work dedicated to methylcyclopentane (MCP) hydrogenolysis, were studied for the methylcyclohexane (MCH) ring opening (RO) performed under high pressure (39.5bar). During MCH transformation, synergetic performances were observed with some supported Pt-Rh bimetallic catalysts, since better performances in terms of activity and RO selectivity were obtained compared to those of monometallic Pt and Rh systems. The metallic particle size acts as a determining parameter modulating the catalytic properties, since the best RO performances were obtained on bimetallic catalysts presenting the largest particle sizes, for which a Pt surface enrichment and the presence of a Pt-Rh alloy were previously detected. On these bimetallic catalysts, the ring opening occurs mainly according to a bifunctional mechanism, the chlorinated alumina support bringing the required acidic function for the first isomerization step of C6 ring to alkylcyclopentanes further opened on the metallic function. The acidic function and the metal sites should not be necessarily in close vicinity since the mechanical mixture of non-acidic Pt-Rh/SiO2 catalyst with chlorinated alumina leads also to high RO selectivities. Finally, as for MCP ring opening, the refilling method allows synthesizing supported bimetallic Pt-Rh catalysts particularly efficient in terms of activity and RO selectivity.

It was previously demonstrated in the first part of this work that NOx storage-reduction process over Pt/BaO/Al2O3 model catalyst is limited by the reduction step, with ammonia emission since H2 is not fully consumed. The stored NOx reacts preferentially with the introduced H2 giving NH3, than with NH3 in order to produce N2. Mn addition favors the NOx reduction with ammonia leading to better conversion and selectivity, but only at 400 °C. In Part II, a special attention was focused on the role of Ce and Mn–Ce addition in regard to the NOx conversion and the ammonia emission in the 200–400 °C temperature range. With ceria modified Pt/20Ba/Al catalyst, significant improvements are obtained from 300 °C. In addition to the enhancement of the NOx + NH3 reaction, the ammonia selectivity is maintained at a lower level compared with Pt/Ba(Mn)/Al catalysts, even in the case of a large H2 excess. It is attributed to the ammonia oxidation into N2 via the available oxygen at the catalyst surface. A synergetic effect is observed between Mn and Ce when they are added simultaneously in Pt/Ba/Al catalyst.

The ammonia selectivity during the cycling NOx storage reduction process over a model Pt/Ba/Al2O3 catalyst was studied. Firstly, it was demonstrated that, whereas the presence of water or carbon dioxide in the gas mixture have a negative effect on the storage step, the effect of these components have different impacts on the NOx efficiency. Due to their involvement in the reverse water gas shift (RWGS) reaction, the absence of water in the gas mixture leads to a drop of the NOx removal whereas without CO2, an increase of the NOx conversion is observed. It was also showed that the reducer (H2) conversion during the short excursion in rich condition is directly correlated to the NH3 emission. NH3 is emitted since hydrogen is not fully converted, whatever the NOx conversion rate. The ammonia pathway is clearly demonstrated and it was claim that, when H2 remains in the reaction mixture, the ammonia production rate is higher than the ammonia reaction with the remaining NOx in order to form N2.

Catalyst supports composed of titania deposited on SBA15 were prepared with titanium oxide loadings varying between 10 and 40 wt.%. Up to 30 wt.% of TiO2, titania was present as highly dispersed anatase nanocrystals in the silica pores, while some segregated titania particles were detected outside the silica network at higher loading (e.g., 40 wt.%). For all the solids, characterization evidenced the preservation of the mesoporous structure after titania deposition, with open porosity, high surface area, large pore size and pore volume. Mo-based oxidic precursors with molybdenum oxide contents of 20 wt.% were then prepared and characterized. Raman spectroscopy evidenced well dispersed polymolybdate species on all the solids whereas bulk MoO3 was also observed on the low TiO2 loading supports. This suggested that high TiO2 loading is necessary to maintain high molybdenum dispersion. A cobalt-molybdenum catalyst deposited on the composite containing 20 wt.% of TiO2 was then tested in thiophene hydrodesulfurization; its performance was found to be superior to those of catalysts based on pure TiO2 and pure SiO2, highlighting the beneficial effect of titanium oxide deposited in the form of nanocrystals inside the mesopores of a SBA15 support

Bimetallic PtZn/CeO2 and PtZr/CeO2 catalysts prepared by impregnation were tested for the selective hydrogenation of citral. Samples with 5wt% Pt and atomic ratio Zn/Pt=Zr/Pt=5 were reduced at 450 degrees C. The monometallic Pt/CeO2 sample was also prepared and studied for comparisons. Samples were analysed by TPR, H-2-chemisorption and cyclohexane dehydrogenation. Their catalytic behaviour was evaluated in the citral hydrogenation reaction after reduction treatments in flowing hydrogen at 450 degrees C. Results obtained show that the presence of Zn clearly promotes the hydrogenation of the carbonyl bond. Large differences in reducibility between catalysts were determined from the TPR results. A modification of the catalytic properties of platinum has been achieved by modifying the Pt/CeO2 catalyst by addition of Zn and Zr.

Bimetallic Pt-Rh catalysts supported on alumina and silica were synthesized either by the refilling method or by coimpregnation They were characterized by transmission electron microscopy (TEM) H-2 chemisorption temperature-programmed reduction (TPR) Fourier transform infrared (FTIR) of adsorbed CO and the test reaction of cyclohexane dehydrogenation Varying the preparation procedure and the nature of the support leads to the formation of bimetallic Pt-Rh particles of different size in the range 1 2-2 7 nm A Pt surface enrichment and the presence of a Pt-Rh alloy were detected by FTIR of adsorbed CO on the largest particlesThe catalytic performances of the Pt-Rh systems were evaluated in methylcyclopentane (MCP) ring opening (RO) under pressure (28 5 bar) All the bimetallic catalysts present an activity much higher than that of the Pt monometallic sample close to that of the Rh one At 300 degrees C the turnover frequencies are the followings 115 h(-1) for Pt 4094 h(-1) for Rh between 2264 and 5563 h(-1) for the Pt-Rh catalysts whatever the preparation procedure and the nature of the support On Pt-Rh samples presenting particles with large enough size (>1 7 nm) the RO selectivity at iso-conversion (>50%) is higher than those of monometallic Pt/Al2O3 and Rh/Al2O3 systems reaching the performances of a monometallic indium-based sample considered as the most selective catalyst in these conditions Finally the refilling method allows obtaining supported Pt-Rh catalysts with the structural properties required to obtain both high activity and RO selectivity during methylcyclopentane hydrogenolysis (C) 2010 Elsevier Inc All rights reserved

LaCoO3-based nanocomposites were prepared by an in situ autocombustion procedure of a glycine–nitrate complex in mesoporous silica supports. For this purpose, two silica supports with different pore sizes (3.0nm for the HMS-type silica; 8.2nm for the SBA15-type silica) were prepared. The final materials were characterized using XRD, TEM, N2-sorption and reactivities evaluated using oxygen isotopic exchange (OIE). One interesting point is the limited pore plugging, due to the low particle size obtained, when synthesis is specifically performed in large pore silica support (SBA15), as suggested by the limited pore volume decrease with respect to the HMS-based system. TEM coupled with EDXS analyses suggest the formation of crystalline mixed-oxide nanoparticles which have been observed with a cobalt to lanthanum ratio always close to 1. These nanoparticles exhibit high oxygen exchange capacity (1.2–2.3 times higher exchange capacities after 60min of reaction), albeit a lower initial rate of exchange compared to the bulk reference sample (due to residual carbonate exchange). At the light of these results, it has been concluded that this method is efficient for producing nanocrystalline particles dispersed in silica pore structure.

This work deals with the effect of Mn or Fe addition on the NO x storage–reduction properties of a Pt/Ba/Al2O3 model catalyst. NO x storage capacity, SO2 poisoning and regeneration and NO x removal efficiency under rich/lean cycling conditions are studied. Fe addition to Pt/Ba/Al2O3 leads only to a small increase of NO x storage capacity, and more interestingly, to a better sulfur removal due to the inhibition of bulk barium sulfate formation. Unfortunately, the NO x storage property cannot be fully recovered. Moreover, Fe addition results in a decrease in the NO x removal efficiency. Mn addition also improves the NO x storage capacity, but no significant influence on the sulfur elimination is observed. Mn-doped catalyst does not improve the NO x removal efficiency, but NH3 selectivity is found to drastically decrease at 400 °C, from 20 to 3%. In addition, the NO x conversion can be improved at higher H2 concentration in the rich pulse, always keeping NH3 selectivity at low level.

Several monometallic catalysts supported on alumina were tested in methylcyclopentane ring-opening under pressure. Among the monometallic catalysts tested (Ru, Re, Rh, Pt and It), iridium and rhodium catalysts were the most active but iridium was by far the most selective in ring-opening (RO) products (2-methylpentane, 3-methylpentane and n-hexane), the formation of C1C5 products being negligible, as already reported in the literature. Thereafter, platinum-based bimetallic catalysts supported on alumina were prepared by redox. surface reaction in order to favor the metal-metal interaction. The aim was to obtain bimetallic catalysts leading to selectivity towards RO products similar to that of the iridium catalyst. Two types of modifiers were studied, namely (i) inactive species such as copper and germanium and (ii) active promoters for hydrogenolysis reactions, such as ruthenium and rhodium. It was shown that with inactive metals, the parent platinum catalyst undergoes mainly a dilution of its active phase. An increase of the activity is observed for the Pt-Ru/Al2O3 systems compared to the parent one, but also an increase of the C1-C5 products. On the contrary, the addition of Rh allowed us to increase the activity of the platinum parent catalyst and to obtain bimetallic catalysts with selectivity towards RO products similar to that obtained with iridium in same conditions. (C) 2009 Elsevier B.V. All rights reserved.

The influence of the ceria-zirconia mixed oxide composition in Pt/CexZr1-xO2 catalysts was studied toward NOx storage capacity (NSC), including sulfur poisoning and sulfur regeneration, and NOx reduction efficiency in lean-rich cycling conditions. The results are compared with a Pt/Ba/Al model catalyst. The samples were characterized by N-2 adsorption, XRD and H-2-TPR. The behaviors of the ceriazirconia supported catalysts are quite similar whatever their composition. They are sensitive to a reducing pretreatment which leads to an increase of (i) the cerium reducibility/oxygen mobility, (ii) the NO oxidation rate and (iii) the NOx storage capacity at 300 and 400 degrees C. The sulfating treatment leads to a dramatic decrease of the NOx storage capacity for all catalysts, the decrease being more pronounced for the Zr-rich samples. H-2-TPR experiments show that the sulfates amount and their stability tend to increase with the Zr content, but these sulfates are significantly less stable compared with Pt/Ba/Al. The sulfur elimination rates in rich mixture at 550 degrees C are higher than 90% with the ceria-zirconia supported catalysts versus 56% with Pt/Ba/Al.The ceria-zirconia supported catalysts are able to convert NOx in lean-rich cycling condition. Compared with Pt/Ba/Al, the NOx conversions are a little lowered but the ammonia selectivity is significantly decreased with the Ce-Zr mixed oxides, with a beneficial influence of the cerium content. (C) 2009 Elsevier B.V. All rights reserved.

Mixtures of equal amounts of a Pt-Rh/Ba/Al2O3 NOx storage reduction (NSR) model catalyst and Ag/Al2O3, Co/Al2O3 or Cu/ZSM-5 selective catalytic reduction (SCR) model catalyst were evaluated for the NOx removal activity under lean-rich atmosphere. NOx removal activity was increased by adding Co/Al2O3 or Cu/ZSM-5 to Pt-Rh/Ba/Al2O3 while adding Ag/Al2O3 had no significant influence. Experiments performed by using two catalytic beds (upstream Pt-Rh/Ba/Al2O3 and downstream Co/Al2O3 or Cu/ZSM-5) suggested that both SCR catalysts are able to reduce NOx with the NH3 produced during the rich step on Pt-Rh/Ba/Al2O3. Among the studied catalysts, the Pt-RhBa/Al2O3 + Cu/ZSM-5 physically mixed one showed the highest activity. This catalyst mixture presented an improved performance, as compared to the NSR catalyst, regardless of the reductant used (CO and/or H-2) or of the reduction time (10, 5 or 2.5 s). The highest activity was obtained by using both CO and H-2 as reductant during the rich pulse. The addition of water in the inlet gas led to a decrease of the NOx removal activity of the catalyst mixture. Nevertheless, the NOx removal activity of the mixed Pt-RhBa/Al2O3 + Cu/ZSM-5 catalyst was still significantly higher than that of Pt-RhBa/Al2O3. (C) 2009 Elsevier B.V. All rights reserved.

Silica-supported Co catalysts with different metal loadings were prepared by water-in-oil (w/o) microemulsion (ME) and tested for the selective hydrogenation of citral. The performances of the ME samples were compared to those of previously studied Co impregnated catalysts. Compared to impregnated Co catalysts, ME samples show more homogeneously dispersed Co particles, the crystallite mean size increasing with the Co content. For the ME samples, the selectivity to unsaturated alcohols (i.e. nerol and geraniol) increases with the metal content then reaches a plateau from approximately 15wt% Co, suggesting that particles of large enough size are required to optimize the CO group activation. Above 15wt% Co content, the selectivity is markedly higher on the ME catalysts compared to the impregnated ones (90% versus 45–65% depending on the nature of the support). This result can be directly related to the higher proportion of β H–Co species detected by temperature-programmed desorption of hydrogen (H2-TPD) on these ME samples.

Mn-based oxide supports were synthesized using different procedures: (i) carbonate co-precipitation method, leading to the formation of a hexaaluminate crystallized solid (La(0.2)Sr(0.3)Ba(0.5)MnAl(11)O(19)) and (ii) solid-solid diffusion method, leading to the formation of a doped theta-Al(2)O(3) crystallized solid (nominal composition: 60 wt% La(0.2)Sr(0.3)Ba(0.5)MnAl(11)O(19) + 40 wt% Al(2)O(3)). Impregnation of 1.0 wt%Pd was carried out on both oxides. The solids were tested for the catalytic methane combustion up to 700 degrees C. It was observed that adding palladium resulted in an important increase in the catalytic activity. The combined use of H(2)-TPR and XPS techniques reveals that only Mn(3+)/Mn(2+) redox "couple" is present in the solids, whatever the synthesis procedure used. The fraction Mn(3+)/Mn is proportional to the total Mn content in the solid support, whatever the sample structure (hexaaluminate or doped theta-Al(2)O(3)) and its morphology (large crystals or aggregates of small particles, respectively). Pd impregnation and further calcination at 650 degrees C has no significant effect on the Mn(3+)/Mn fraction. However, some changes in Mn(3+) reduction profile are observed, depending on the solid structure. Indeed, palladium addition strongly affects the manganese reducibility with an important shift of the reduction process to lower temperatures (approximately 100 degrees C). On the basis of redox properties observed for the different catalysts, a Mars-van-Krevelen redox mechanism, with oxygen transfer from support oxides to palladium particles, is proposed to explain the difference in terms of catalytic conversion and stability with respect to a 1.0 wt%Pd/Al(2)O(3) reference sample.

The influence of both the support oxide (Al2O3, SiO2, Al2O3-5.5 wt% SiO2 and Ce0.7Zr0.3O2) and the barium loading of Pt/Ba/Support model catalysts on sulfur resistance was investigated by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD) and NOx storage capacity measurements. The sulfation of catalysts under lean conditions in the presence of water and carbon dioxide led to the formation of both surface and bulk sulfates, except for silica supported catalyst on which mainly bulk barium sulfates were formed. Sulfate stability was influenced by the support oxide and the Ba loading. For alumina containing catalysts, both the amount of deposited sulfur and the sulfate stability under hydrogen increase with the Ba loading. Conversely the same sulfates stability was observed for Ce-Zr supported samples, whatever the Ba loading. The thermal treatment of the sulfated catalysts under oxidizing conditions at 800 degrees C favored the formation of less reducible bulk barium sulfates on all the catalysts. Ceria-zirconia led to a decrease of bulk BaSO4 stability under hydrogen, their reduction temperature being about 100 degrees C lower than on alumina containing materials. The elimination of sulfates under rich conditions (H-2, CO2, H2O, N-2) was more effective on the ceria-zirconia supported sample compared to alumina containing catalysts, even after ageing at 800 degrees C.Sulfation of the catalysts induced a loss of NOx storage capacity depending on catalyst composition. All the catalysts recovered their initial NOx storage capacity after regeneration at 550 degrees C, even with an improvement in the case of the ceria-zirconia supported material. The ageing at 800 degrees C of sulfated catalysts before regeneration did not lower the performance of the Pt/10Ba/CeZr catalyst, contrary to the alumina containing samples. (C) 2007 Elsevier B.V. All rights reserved.

The influence of a pre-treatment at 700°C, either under a O2/N2 mixture or only under N2, and followed by a hydrothermal aging at 700°C under wet air, was studied for Pt/Ba/Al NSR model catalysts prepared by different methods: (i) successive impregnation of Ba and Pt, (ii) co-addition of Pt and Ba and (iii) barium precipitation followed by Pt impregnation. The catalysts were evaluated by NOx storage capacity measurements and were characterized by N2 adsorption, XRD, CO2-TPD, H2 chemisorption and H2-TPR. The pre-treatment under N2 largely improves the NOx storage performance in the whole studied temperature range (200–400°C), with or without H2O and CO2 in the inlet gas. The better NOx storage properties of the catalysts treated under N2 before aging are due to: (i) a higher NO oxidation activity (mainly linked to a higher platinum dispersion), (ii) a higher number of NOx storage sites resulting from a higher barium dispersion, and consequently to (iii) a higher Pt-Ba proximity.

NOx removal efficiency was investigated with a combination of model Pt–Rh/Ba/Al and Cu-ZSM-5 catalysts using periodic fluctuations between lean (100s) and rich (10s) atmosphere. NOx removal is greatly improved at 250°C and 300°C by physically mixing the two catalysts. The mixed catalyst shows a NOx removal activity almost double as compared to a system where Pt–Rh/Ba/Al catalyst is situated upstream and CuZSM-5 downstream the gas flow. FT-IR characterisation shows that CuZSM-5 catalyst enhances the formation of NCO species on alumina during rich conditions. These NCO are further hydrolyzed to NH3 under lean condition which acts as a reductant for NOx.

Materials with high 'oxygen storage capacity' (OSC) are now widely used in automotive converter catalysts. They are mainly composed of Ce-based oxides (CeZrOx, CeZrPrOx, etc.) having both multiple cationic valencies and oxygen vacancies. These properties allow the catalyst to store active O species (O2-, superoxide, etc.) in O-2 excess and to release them when the O-2 concentration in gas phase decreases or becomes nil. After having briefly examined the main properties of these OSC materials and the methods employed for their characterization, their impact in automotive catalysis will be reviewed, with a special insight in DeNO(x) catalysis: (1) in three-way catalysis (2) in automotive catalysis under lean conditions (lean-bum spark ignition engine and diesel).