Temperature-programmed Reduction Profiles Research Articles

Thermal behaviour of Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides and characterization of formed oxides

Thermal behaviour of synthetic Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides (LDHs) with M II/Mg/Mn molar ratio of 1:1:1 was studied in the temperature range 200–1100 °C by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), Raman spectroscopy, and voltammetry of microparticles. Powder XRD patterns of prepared LDHs showed characteristic hydrotalcite-like phases, but further phases were indirectly found as admixtures. The Cu–Mg–Mn precipitate was decomposed at temperatures up to ca. 200 °C to form an XRD-amorphous mixture of oxides. The crystallization of CuO (tenorite) and a spinel type mixed oxide of varying composition Cu x Mg y Mn z O 4 with Mn 4+ was detected at 300–500 °C. At high temperatures (900–1000 °C), tenorite disappeared and a consecutive crystallization of 2CuO·MgO (gueggonite) was observed. The high-temperature transformation of oxide phases led to a formation of Cu I oxides accompanied by oxygen evolution. The DTA curve of Ni–Mg–Mn sample exhibited two endothermic effects characteristic for hydrotalcite-like compounds. The first one with minimum at 190 °C can be ascribed to a loss of interlayer water, the second one with minimum at 305 °C to the sample decomposition. Heating of the Ni–Mg–Mn sample at 300 °C led to the onset of crystallization of oxide phases identified as Ni x Mg y Mn z O 4 spinel, (Ni,Mg)O oxide containing Mn 4+ cations, and easily reducible XRD-amorphous species, probably free Mn III,IV oxides. At 600 °C (Raman spectroscopy) and 700 °C (XRD), the (Ni,Mg) 6MnO 8 oxide with murdochite structure together with spinel phase were detected. Only spinel and (Ni,Mg)O were found after heating at 900 °C and higher temperatures. Temperature-programmed reduction (TPR) profiles of calcined Cu–Mg–Mn samples exhibited a single reduction peak with maximum around 250 °C. The highest H 2 consumption was observed for the sample calcined at 800 °C. The reduction of Ni–Mg–Mn samples proceeded by a more complex way and the TPR profiles reflected the phase composition changing depending on the calcination temperature.

Characterisation by TPR, XRD and NOxStorage Capacity Measurements of the Ageing by Thermal Treatment and SO2Poisoning of a Pt/Ba/Al NOx-Trap Model Catalyst

The deactivation of a Pt/Ba/Al2O3 NO x -trap model catalyst submitted to SO2 treatment and/or thermal ageing at 800 °C was studied by H2 temperature programmed reduction (TPR), X-ray diffraction (XRD) and NO x storage capacity measurements. The X-ray diffractogram of the fresh sample exhibits peaks characteristic for barium carbonate. Thermal ageing leads to the decomposition of barium carbonate and to the formation of BaAl2O4. The TPR profile of the sulphated sample shows the presence of (i) surface aluminium sulphates, (ii) surface barium sulphates, (iii) bulk barium sulphates. The exposure to SO2 after ageing leads to a small decrease of the surface barium-based sulphates, expected mainly as aluminate barium sulphates. This evolution can be attributed to a sintering of the storage material. TPR experiments also show that thermal treatment at 800 °C after the exposure to SO2 involves the decomposition of aluminium surface sulphates to give mainly bulk barium sulphates, also pointed out by XRD. Thus, the thermal treatment at 800 °C leads to a stabilization of the sulphates. These results are in accordance with the NO x storage capacity measurements. On non-sulphated catalysts, the treatment at 800 °C induces to a decrease of the NO x storage capacity, showing that barium aluminate presents a lower NO x storage capacity than barium carbonate. Sulphation strongly decreases the NO x storage capacity of catalysts, whatever the initial thermal treatment, showing that barium sulphates inhibit the NO2 adsorption. Moreover, the platinum activity for the NO to NO2 oxidation is lowered by thermal treatments.

Catalytic activity of Mo/MgO catalyst in the wet oxidation of H 2S to sulfur at room temperature

The Mo/MgO catalysts with different MoO 3 loadings were prepared by impregnating MgO support with aqueous ammonium heptamolybdate solution. They were characterized by BET surface analysis, X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The highest removal capacity of H 2S was obtained with a molybdenum content of 6 wt.%, which was almost close to the theoretical monolayer capacity on MgO support. The surface coverage calculation of MoO 3 suggested that a molybdenum oxide addition up to a monomolecular layer on MgO support increased the H 2S removal capacity of Mo/MgO, but that further increase of Mo–O surface coverage rather decreased it. Raman spectroscopy showed that small domains of MgMoO 4 could be present on Mo/MgO with molybdena loadings below 6 wt.%. The crystallites of bulk MgMoO 4 and Mg 2Mo 3O 11 became evident on Mo/MgO with molybdena loadings above 15 wt.%, which were confirmed by XRD. TPR profiles showed that the reducibility of Mg molybdate phases was strongly related to the loading amounts of MoO 3 on MgO support. Results indicated that tetrahedrally coordinated Mo 6+ in well-dispersed MgMoO 4 domains could be the active species in the H 2S wet oxidation. XPS studies indicated that the H 2S oxidation with Mo/MgO could proceed from the redox mechanism (Mo 6+↔M 5+) and that Mo 4+ formation, deep reduction, was responsible for the deactivation of Mo/MgO.

Synthesis and characterization of the reduction properties of cobalt-substituted lanthanum orthoferrites

Perovskite-related materials of composition LaFe 1− x Co x O 3 have been prepared by conventional calcination methods. The temperature programmed reduction profiles indicate that the incorporation of cobalt renders the materials more susceptible to reduction when treated in a flowing mixture of hydrogen and nitrogen. The reduction processes have been examined by 57Fe Mössbauer spectroscopy and Fe K-edge-, Co K-edge- and La L III-edge XANES and EXAFS. The results show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure at temperatures up to 1200°C. In materials where x⩾ca.0.5 the reduction of Co 3+ to Co 0 precedes complete reduction of Fe 3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure.

Low temperature reductive pretreatment of Au/Fe 2O 3 catalysts, TPR/TPO studies and behaviour in the water–gas shift reaction

The Au/Fe 2O 3 catalyst is prepared by a deposition–precipitation method and reduced using different organic/inorganic precursors before the measurement for low temperature water–gas shift reaction (WGSR). Addition of 2,6-dimethylpyridine to the water–gas mixture decreases the WGS activity suggesting the involvement of surface hydroxyl groups in the WGS reaction. Temperature programmed reduction (TPR) analysis revealed reduction signals due to oxidic-gold species and changes in TPR profiles were seen after treatment with organic/inorganic reducing agents. Catalysts were treated with different reducing agents and some of them were characterized by BET-surface area, TEM analysis and TPR/TPO studies. An HF treated Au/Fe 2O 3 sample showed lower activity compared to the catalyst made by conventional methods. A microwave irradiated sample showed lower WGSR activity compared to a conventionally heated catalyst. Based on the experimental observations and from TPR2 analysis of the microwave irradiated sample, it is concluded that Au is redispersed after TPR1 and with the subsequent exposure to oxygen during TPO analysis. TEM analysis revealed that the average particle size of fresh 3 wt.% Au/Fe 2O 3 catalyst is ca. 15 nm, which is increased to 32 nm in the spent catalyst form.

Nitrate anions intact in calcination treatment of Pt/NaMOR catalysts: a temperature-programmed reduction study

Samples of nitrate-ion exchanged NaMOR (NaM) i.e., HNO 3/NaM, NaNO 3/NaM and Pt/NaM were prepared by ion exchange of NaM with respective nitrate precursors––HNO 3, NaNO 3 and [Pt(NH 3) 4](NO 3) 2. The prepared samples were calcined at a temperature of T c∼723 K in flowing air to decompose nitrate anions and then studied by temperature-programmed reduction (TPR) technique. A reduction peak around T r=830±40 K invariably appeared in TPR profiles of calcined samples. This peak is assigned to reduction of nitrate anions remained intact on the calcination and adsorbed on zeolitic sodium cations during the ion exchange. In addition, the calcined Pt/MOR sample showed a sharp peak around T r=360 K due to reduction of PtO in channels of NaM.

Preparation, characterization, and activity of Al 2O 3-supported V 2O 5 catalysts

A series of activated alumina-supported vanadium oxide catalysts with various V 2O 5 loadings ranging from 5 to 25 wt% have been prepared by wet impregnation technique. A combination of various physicochemical techniques such as BET surface area, oxygen chemisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermal gravimetric analysis (TGA), and Fourier transform infrared (FTIR) were used to characterize the chemical environment of vanadium on the alumina surface. Oxygen uptakes were measured at 370 °C with prereduction at the same temperature, which appears to yield better numerical values of dispersion and oxygen atom site densities. XRD and FTIR results suggest that vanadium oxide exists in a highly dispersed state below 15 wt% V 2O 5 loading and in the microcrystalline phase above this loading level. TPR profiles of V 2O 5/Al 2O 3 catalysts exhibit only a single peak at low temperature up to 15 wt% V 2O 5. It is suggested that the low-temperature reduction peak is due to the reduction of surface vanadia, which has been ascribed to the tetrahedral coordination geometry of the V ions. TPR of V 2O 5/Al 2O 3 at higher vanadia loadings exhibited three peaks at reduction temperatures, indicating that bulk-like vanadia species are present for these catalysts only at higher vanadia loadings, with V ions in an octahedral coordination. The TPR profiles of V 2O 5/Al 2O 3 catalysts indicate that at loadings lower than 15% vanadia forms isolated surface vanadia species, while two-dimensional structure and V 2O 5 crystallites become prevalent in highly loaded (>15% V 2O 5) systems. Liquid-phase oxidation of ethylbenzene to acetophenone has been employed as a chemical probe reaction to examine the catalytic activity. Ethylbenzene oxidation results reveal that 15%V 2O 5/Al 2O 3 is more active than higher vanadia loading catalysts.

Effects of potassium addition on the acidity and reducibility of chromia/alumina dehydrogenation catalysts

Dehydrogenation catalysts based on chromia supported on γ-alumina, containing about 6 wt.% of chromium and increasing amounts of potassium (up to 1.8 wt.%), were prepared and characterised by means of several techniques, such as N 2 adsorption at 77 K, X-ray powder diffraction (XRPD), UV-Vis diffuse reflectance spectroscopy (DRS), electron paramagnetic resonance (EPR), temperature programmed reduction (TPR), microcalorimetry and chemical analyses. The catalytic behaviour of the samples was investigated in the propane dehydrogenation reaction at 813 K and the effect of potassium loading was examined. The addition of increasing amounts of the alkali metal, as expected, determined a general decrease in the surface acidity. The sites strength distribution was greatly influenced, due to the fact that, at loadings above 0.5 wt.%, potassium preferentially caused the disappearance of weak and medium acid sites. EPR showed a decrease of Cr III species (especially α-Cr 2O 3) on potassium increasing. TPR profiles of the K-containing samples showed the presence of two reduction peaks, ascribable to two different kinds of Cr VI surface species with a different reduction behaviour. All catalysts showed a maximum of activity as a function of time-on-stream, due to reduction of Cr VI to Cr III species in the first reaction period, and then a decrease, due to deactivation by coking. Propene selectivity was high in all cases and was positively affected by the presence of potassium in concentrations up to 1 wt.%.

Optimization of Tailoring of CuOx Species of Silica Alumina Supported Catalysts for the Selective Catalytic Reduction of NOx

A series of CuOx catalysts dispersed on SiO2−Al2O3 support with a copper content from 0.2 to 12 wt % corresponding to 0.04−3.7 atomCu nm-2 was prepared by chemisorption-hydrolysis method from copper solutions. The catalysts were characterized in their bulk (XRD, redox cycles with H2 and O2) and surface (N2 adsorption, SEM, XPS, and DRS) properties. Copper species were found to be uniformly spread on the SiO2−Al2O3 support as small aggregates both in the low and high copper loaded samples. Spectroscopic evidence agrees with Cu2+ presence in an axially distorted octahedral environment of O-containing ligands. At high copper loading, the existence of copper centers in closer interaction occurred forming structures of oxocations-like type. Temperature programmed reduction (TPR) experiments confirmed the presence of dispersed copper species which underwent complete reduction. Comparing the position and shape of two successive TPR profiles, carried out interposing an oxidation run (temperature programmed oxidation), it was found that the smallest CuOx centers (<1 atomCu nm-2) are characterized by low stability and high mobility. Increasing the copper content diminished the mobility of the CuOx species, as larger CuOx aggregates were formed. The selective catalytic reduction of NOx with ethene in the presence of excess oxygen was studied in a flow apparatus at fixed reactant concentration (1500 ppm of NOx and C2H4 and 15000 ppm of O2) and contact time (8 g s mmol-1), with an online FT-IR analytical device. Catalysts containing up to about 1 atomCu nm-2 displayed very little activity, while catalysts with higher copper content were active and selective. Maximum activity was associated with samples containing 1.5−2 atomCu nm-2, while samples with higher copper concentration were less active. Results point to the need to individuate relationships between structure and catalyst properties and activity to optimize the preparation of suitable tailored copper-containing catalysts.

Release and uptake of oxygen in mixed-conducting SOFC cathode materials measured by temperature-programmed methods

Oxygen uptake and release in A1−aA′aB1−bB′bO3−δ perovskite-type oxides with A=La, Pr; A′=Sr; B=Fe, Mn, B′=Co was examined by means of temperature-programmed oxidation (TPO) and temperature-programmed reduction (TPR). The investigated powders were prepared by spray-drying and were annealed at 900 to 1300 °C. In the TPR profiles, two processes of oxygen release from these materials were observed. The first TPR peak was regarded as surface adsorption, while the second one was considered to result from oxygen bulk diffusion. The oxygen volumes involved and the activation energy for the oxygen diffusion were determined from the TPO and TPR profiles and varied between 0.53 and 2.2 eV for the ferrites and manganites, respectively.

Cobalt catalysts for the oxidation of diesel soot particulate

Ceria-supported materials prepared by three routes, coprecipitation from aqueous solution containing both Co 2+ and Ce 3+ ions, and impregnation of preformed ceria gel with either cobalt(II) nitrate or cobalt(II) acetate, have been investigated for catalytic activity towards oxidation of diesel soot. All three materials catalyze the conversion of diesel soot particulate to carbon dioxide under a flow of either 6 vol.% O 2 or 0.5 vol.% NO + 6 vol.% O 2 in helium in the temperature range 573–613 K. The temperature of maximum conversion rate shows a small dependence on the particular catalyst and the composition of the oxidant. Raman spectroscopy of the ceria-supported cobalt catalysts indicate that the cobalt is present as Co 3O 4, but its average particle size in Co/CeO 2 impregnated with Co acetate is smaller than the other two Co/CeO 2 preparations. Features in the temperature-programmed reduction (TPR) profiles in the range 500–600 K, coincident with the temperature of catalytic activity, appear to be associated with reduction of the cobalt, suggesting a redox-type mechanism assisted by oxygen spillover on the CeO 2 support. In contrast, cobalt supported on alumina, silica, and tin(IV) oxide obtained by coprecipitation show much lower activity due to the presence of dispersed Co 2+ ions in these materials although small amounts of Co 3O 4 may be present on alumina and tin(IV) oxide.

Characterization and reactivity of vanadium oxide catalysts supported on niobia

A series of V 2O 5/Nb 2O 5 catalysts with vanadia loading varying from 2 to 12 wt.% were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), BET surface area and oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidation of 3-picoline to nicotinonitrile. XRD results suggest the formation of β-(Nb,V) 2O 5 phase at higher loadings. TPR profiles showed two peaks: the low temperature peak is due to reduction of surface vanadia species and the high temperature peak is due to reduction of Nb 2O 5. XPS results reveal that both vanadia and niobia are present in fully oxidized state (5+) in all the samples. The intensity ratio V 2p 3/2:Nb 3d 5/2 is found to increase with increase in vanadia loading up to 6 wt.% and to remain constant at higher vanadia loadings. The oxygen uptake increases with increase of vanadia loading on niobia, whereas the dispersion of vanadia decreases. The dispersion of vanadia measured by oxygen chemisorption method is in good agreement with the dispersion determined from XPS. The ammoxidation activity increases with vanadia loading up to 6 wt.%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic properties during ammoxidation of 3-picoline are related to the oxygen chemisorption sites.

Investigation of the interaction between NiO and yttria-stabilized zirconia (YSZ) in the NiO/YSZ composite by temperature-programmed reduction technique

Temperature-programmed reduction (TPR) was performed to investigate the reducibility of the NiO/YSZ composite that is related to the anode of solid oxide fuel cells (SOFCs). The TPR profiles were found to be affected by preparation method, composition and pretreatment conditions. The calcination temperature strongly affected the reduction behavior; the TPR profile of the sample calcined at 1723 K shows a high temperature reduction peak that was not found in the TPR profile of the sample calcined at 1473 K. Such a difference in the TPR profiles can be attributed to the presence of distinct states of NiO species, which are due to the difference of interactions between NiO and YSZ. Five distinct states of NiO species are shown to be present in the NiO/YSZ composite.

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce1-xCuxO2-δ mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce1-xCuxO2-δ mixed oxides indicated that Cu2+ ions were dissolved in CeO2 lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO2 promotes the reduction of the Cu2+ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu2+ species in the Ce1-xCuxO2-δ mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu2+ species which dissolved into the CeO2 lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO2. The Ce1-xCuxO2-δ mixed oxides were reduced to form Cu/CeO2 catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL2O3 catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO2 (over 97%) and H2. A 3.8wt% Cu/CeO2 catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL2O3 (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO2 catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO2 support. Slow deactivations were observed over the 3.8wt% Cu/CeO2 catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H2 at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO2 catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.

Influence of oxidizing and reducing treatments on the metal–metal interactions and on the activity for nitrate reduction of a Pt-Cu bimetallic catalyst

Bimetallic Pt-Cu/γAl 2O 3 catalyst has been prepared by controlled deposition of copper onto platinum particles according to a redox reaction between hydrogen, pre-adsorbed on metallic platinum, and Cu 2+ ions in water. This catalyst has been submitted to either oxidizing or reducing treatments, at ambient temperature or at 400 °C. The interaction between copper and platinum in the bimetallic catalysts was estimated from temperature-programmed reduction (TPR) profiles, determined after various pre-treatments, and compared to that of a fresh catalyst. It was demonstrated that reducing and oxidizing pre-treatments noticeably affect the interactions between platinum and copper and consequently the catalytic activity for nitrate reduction in water.

Study of reverse water gas shift reaction by TPD, TPR and CO 2 hydrogenation over potassium-promoted Cu/SiO 2 catalyst

The reverse water gas shift (RWGS) reaction over Cu/SiO 2 with and without potassium promoter was studied by means of CO 2 hydrogenation, temperature programmed reduction (TPR) and temperature programmed desorption (TPD). After addition of even a little amount of potassium, Cu/K 2O/SiO 2 obviously offers better catalytic activity than Cu/SiO 2. The coverage of formate species increases on Cu/K catalyst. TPD of CO 2 adsorbed on Cu/K 2O/SiO 2 and TPR profile of Cu/K 2O/SiO 2 showed that new active sites could be created at interface between Cu and K. The main role of K 2O was to provide catalytic activity for decomposition of formates, besides acting as a promoter for CO 2 adsorption. A new reaction mechanism was suggested. Hydrogen was dissociatively adsorbed on Cu and could spill over to K 2O to associate with CO 2. This resulted in the formation of formate species for the production of CO.

The promotion of cobalt mordenite by palladium for the lean CH 4-SCR of NO x in moist streams

The promotional effect of palladium on the catalytic performance of cobalt ion exchanged mordenite (Co-HMOR) for the lean NO x reduction with methane in a wet reaction stream was evaluated. The addition of 0.1–0.15 wt.% Pd to Co-HMOR samples containing high Co 2+ levels lead to a material that can convert 60% NO to N 2 and 60% CH 4 to CO 2 at 500 °C in a reaction mixture containing 1000 ppm NO, 2700 ppm CH 4, 6% O 2, and 8% H 2O, at GHSV=30 000 h −1. NO reduction over Pd/Co-HMOR increases with Co loading up to about 90% cobalt exchange. The increase of Pd loading to Co-HMOR favors methane combustion instead of NO reduction. Experiments of NO oxidation to NO 2 in the presence of 2% water vapor show that the addition of Pd to Co under-exchanged samples produces much less NO 2 than was found under the same conditions on cobalt over-exchanged samples loaded with small amounts of Pd. On the other hand, almost total NO reduction to nitrogen was obtained between 500 and 550 °C in the oxygen free feed (CH 4+NO+H 2O). The nature of the active species was investigated by XPS and TPR. Results from XPS reveal that cobalt is uniformly distributed as Co 2+ in fresh Pd/Co-HMOR samples but, Pd exists as Pd 0 and Pd 2+ on the surface. The addition of Pd to Co-HMOR shifts the maxima in the temperature-programmed reduction profiles to lower temperatures and increases the reducibility of Co 2+ cations at exchange positions.

Effects of thermal pretreatment on the redox behaviour of Ce0.5Zr0.5O2: isotopic and spectroscopic studies

The temperature programmed reduction (TPR) of a single phase Ce0.5Zr0.5O2 solid solution is investigated by using 1H2/Ar and 2H2/Ar mixtures as reducing agents. The effects of mild (700 K) or severe (1273 K) pre-oxidation (MO, SO) on the TPR profile are analysed. It is observed that after SO pretreatment hydrogen activation/scrambling occurs at about 600 K and the reduction profile is characterised by a single reduction peak at 920 K. In contrast, a TPR/MO pretreatment of such SO sample leads to a facile hydrogen activation/scrambling and low temperature reduction profiles, the main reduction peak being observed at ca. 650 K. Using 1H2 and 2H2 as reducing agents, an isotopic effect is observed for the reduction processes with a peak occurring above 700 K, while equal activation energies are measured for those occurring below 700 K. This suggests that under the TPR conditions the surface reduction steps (activation of the reducing agent at the surface, surface reduction steps and water evolution) are not rate limiting for the low temperature reduction process, which is controlled by bulk diffusion, while some surface step (probably water formation) is limiting for the high temperature reduction. Studies by EPR on the nature of the oxygen species adsorbed on variously pretreated specimens and by FTIR of the methoxy species formed upon methanol adsorption on the same materials reveal that the main changes induced by high temperature calcination are related to segregation of ceria- and zirconia-type islands, with some surface enrichment in cerium probably occurring as well. Only subtle differences between SO and MO pretreated samples can be detected at either surface or bulk (XRD experiments) levels, in contrast with the significant modifications produced by the different pretreatments on the reduction characteristics of the sample.

Highly active copper/ceria catalysts for steam reforming of methanol

The Ce 1− x Cu x O 2− x mixed oxides were synthesized using the coprecipitation method. The X-ray diffraction (XRD) patterns and the temperature-programmed reduction (TPR) profiles indicated that the Cu 2+-ions were dissolved into the CeO 2 lattices to form a solid solution by calcination at 723 K when x<0.2 in the Ce 1− x Cu x O 2− x mixed oxides. The Ce 1− x Cu x O 2− x mixed oxides were reduced to form the Cu/CeO 2 (cop) catalysts for the steam reforming of methanol. The activity and selectivity of Cu/CeO 2 (cop) were compared with those of Cu/ZnO, Cu/Zn(Al)O and Cu/Al 2O 3. All the Cu-containing catalysts tested in this study showed high selectivities to CO 2 (over 97%) and H 2. A 3.9 wt.% Cu/CeO 2 (cop) catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513 K, which was higher than the conversions over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/Al 2O 3 (11.2%) with the same Cu loading under the same reaction conditions. The high activity of the 3.9 wt.% Cu/CeO 2 (cop) catalyst may be due to the highly dispersed Cu metal particles and the Cu + species stabilized by the CeO 2 support. Slow deactivation was observed over the 3.9 wt.% Cu/CeO 2 (cop) catalyst at 493 and 513 K. The activity of the deactivated catalysts can be regenerated by calcination in air at 723 K, followed by reduction in H 2 at 673 K. Such success indicated that the carbonaceous deposit on the catalysts surface caused the catalysts’ deactivation. The temperature-programmed oxidation (TPO) method indicated that the amounts of coke on the 3.9 wt.% Cu/CeO 2 (cop) catalyst were 0.8 wt.% at 493 K and 1.7 wt.% at 513 K after 24 h on stream.

Pd/Al2O3-La2O3 catalysts prepared by sol–gel: characterization and catalytic activity in the NO reduction by H2

The 0.3%Pd/Al2O3-La2O3 (0, 6 and 15wt.% La2O3) catalysts prepared by the sol–gel method were studied by N2 physisorption, X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and temperature-programmed reduction (TPR). The catalysts were tested in the reduction of NO by H2. Results indicate that the texture and structure of Pd catalysts are modified by the addition of lanthana. The TPR profiles of the catalysts show reduction peaks at 100 and 150°C, suggesting that the reduction of crystalline PdO occurs in two stages: first to Pd2O, and then to Pd0. After recalcination of the samples, the reducibility properties are modified. One reduction peak appears at 360°C that can be assigned to the presence of a more stable surface PdO phase interacting strongly with lanthana species. The presence of metallic Pd and Pd3La alloy species in the Pd/Al2O3-La2O3 catalysts was detected after reduction at high temperature. These species present particle sizes of 77 and 130Å. Pd3La alloy species are present also as crystallites of 20Å. The modification of the reducibility properties of the catalysts influences the activity in the NO reduction by hydrogen. The selectivity depends on the extent of interaction between Pd and lanthana reduced species. For the Pd/Al2O3-La2O3 catalysts, the selectivity to N2 is high at temperatures lower than 250°C. The strong interaction between Pd and lanthana species, forming Pd3LaOx species, may be responsible for the increase in activity and selectivity to N2.