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Two ternary mixed oxides, Ru-Mn-Ce and Ru-Co-Ce, were prepared by a co-precipitation method and used in the aerobic oxidation of alcohols to corresponding aldehydes (ketones). Interestingly, different catalytic results were obtained when these compounds were calcined. The calcination temperature had an adverse effect on the catalytic performance of Ru-Mn-Ce catalysts, while being beneficial to the Ru-Co-Ce catalysts. To illustrate these effects, these materials were characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Temperature-programmed reduction (TPR), Electron paramagnetic resonance (EPR) and other techniques. The data showed that ruthenium oxides were uniformly dispersed in the mixed oxides, and phase transformations occur after calcination. Mn 3 O 4 was transformed to MnO 2 for the Ru-Mn-Ce catalyst, while CoO(OH) was transformed to Co 3 O 4 in the Ru-Co-Ce catalyst . The interactions between ruthenium oxides and Co (Mn)-Ce mixed oxides of the former strengthened while the latter weakened. Calcination decreased the content of adsorbed oxygen and restricted oxygen transfer mechanism in the manganese system, while the opposite effect was observed with the cobalt-containing catalyst. Under optimal reaction conditions, various kinds of alcohols were transformed to corresponding aldehydes (ketones) in high yields over the Ru-Mn-Ce catalyst suggesting these ternary oxides are environmental friendly and economical catalytic systems. [ABSTRACT FROM AUTHOR]

Mixed oxide catalysts composed of mixtures of La 1+ x FeO 3+ δ perovskite and La 2 O 3 were prepared using the auto-combustion method with glycine as an ignition promoter. A series of samples was prepared with x = 0, 0.1, 0.3, 0.5, 0.8 and 1, which were hereafter called La 1+ x Fe. The as-prepared powders were characterized by XRD, XPS, DTA-TGA and N 2 -physisorption. Their acid-base properties were evaluated from their 2-propanol reactivity. Surface enrichment in La 2 O 3 was detected when the lanthanum content increased. For high lanthanum concentrations, lanthanum hydroxide was also formed. The highest ethanol conversion was observed over La 1.3 Fe (32% at 400 °C), which contained the largest amount of basic sites. The main reaction products were ethylene, acetone, 2-pentanone and 1-butanol. Other minor products originating from dehydration, reverse aldolization and hydrogenation reactions were also detected. Such a diversity of products was due to the presence of different kinds and distribution of sites on the catalysts surface (acid, base, hydrogenation, etc. ). The catalysts activity was depending on their acid-base properties: an increase in the basic character due to the La 2 O 3 presence at the surface leaded to higher selectivities to 1-butanol and 2-pentanone, which were 6 and 31% at 400 °C, respectively, over the sample with the highest number of basic sites, which were also stronger (La 1.3 Fe). On the other hand, over La 1.8 Fe, which contained the highest quantity of La(OH) 3, lower selectivities to 1-butanol and 2-pentanone (4.3 and 22%, respectively) were observed due to a decrease in the number of basic sites, together with a high ethylene selectivity (37%), with thus a predominant action of acid sites. [ABSTRACT FROM AUTHOR]

The gas-phase upgrading of 2-hexanol, a model molecule of the primary conversion of sugars, toward higher molecular weight compounds of application as liquid transportation fuels was investigated on Cu–M I –M II mixed oxides (M I , M II : Mg 2+ , Al 3+ , Ce 4+ ) at 573 K and 101.3 kPa. Catalysts were prepared by coprecipitation and characterized by several techniques such as BET surface area, XRD, TPD of CO 2 and NH 3 , TPR and N 2 O decomposition. The bifunctional metal–base catalytic process occurs through a series of sequential steps comprising dehydrogenation, C C coupling, dehydration and hydrogenation reactions. Nano-sized Cu 0 particles promote dehydrogenation and hydrogenation steps whereas acid–base sites provided by M I (M II )–O pairs participate in the C C coupling reaction. In general, main products were C9–C12 compounds that represented ∼60% of the product pool. Branched C9–C24 compounds such as ketones, alcohols and alkanes were obtained with yields of up to 91% on a Cu–Mg–Al mixed oxide with 8 wt.% Cu (catalyst 8.0CuMgAl). This catalyst presented well dispersed Cu 0 particles and a high number of base sites with moderate basic properties as well as a low number of acid sites. The rate-limiting step of the bifunctional process leading to C9–C24 products on catalyst 8.0CuMgAl was the metal-promoted hydrogenation step, but the reaction can be controlled by the C C bond formation step on less basic catalysts. By carrying out experiments under different reaction atmospheres (N 2 or H 2 ) and at different contact times, a reaction pathway leading to formation of odd carbon atom number products (C9, C15 and C21) is postulated in contrast to the conventional aldol condensation pathway toward even carbon atom number products (C12, C18 and C24). The former prevails under conditions at which the catalyst surface is deprived of hydrogen atoms. [ABSTRACT FROM AUTHOR]

The production of higher alcohols (C4+) via ethanol liquid-phase condensation is studied in this work, screening catalysts with different acid/base properties, observing similarities but also relevant differences with respect to gas-phase reactions in the gas phase. The mechanistic analysis demonstrates the relevance of acidity, mainly to promote the dehydrogenation steps. In the same way, side reactions and hydrogenations have less relevance than in gas-phase, promoting the condensations and, subsequently, obtaining heavy compounds. The highest alcohol selectivity is reached with MgAl (2/1), with more than 79% of C4+ selectivity, but the activity of this material is conditioned by the low conversion obtained. The presence of water reduces the activity because of a competitive adsorption on the catalytic sites whereas the activity increases significantly when using bifunctional catalysts. The best results, obtained with 1% Cu/MgAl (2/1), allow rising the conversion up to more than 460% respect to the parent mixed oxide, with almost 44% of the alcohol mixture enriched in heavy compounds, mainly C6 and C8. [Display omitted] • Liquid-phase solvent-free ethanol condensation in batch reactor. • Butanol is the main condensation product. • Significant yields to C6 and C8 alcohols. • Water severely inhibits condensation reactions. • The presence of metal active phase increase reaction rates. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Co–Mn–Al LDH precursors were deposited on anodized aluminum foils. [•] The Mn/Co ratio of 4–8 in solutions was favorable for obtaining active catalysts. [•] Supported mixed oxide catalysts were tested in the total oxidation of ethanol. [•] The catalysts specific activity increased with increasing the Mn/Co ratio in solid. [•] Specific activity of supported catalysts was higher than that of the grained one. [Copyright &y& Elsevier]

Highlights: [•] Rare earth cation-containing layered double hydroxides as catalyst precursors. [•] Effective catalysts for methane total oxidation. [•] The Ce-containing catalyst was the most active. [•] The catalytic activity depended on the Ce content. [•] The catalyst reducibility played a key role in the catalytic reaction. [Copyright &y& Elsevier]

Abstract: MMgAlO mixed oxide catalysts (M=Mn, Fe, Co, Ni, Cu, Zn, Ag and Pd) obtained from layered double hydroxide (LDH) precursors calcined at 1023K were used in the complete oxidation of methane and the oxidative dehydrogenation of propane. The catalysts were characterized by XRD, N2 adsorption, EDX and H2-TPR experiments. In the catalytic complete oxidation of methane, the Pd-based catalyst has been proved the most active, but the less stable catalyst. Other mixed oxides containing transition metals have been tested and their catalytic activity followed the order: MgAlO≈FeMgAlOMnMgAlO>NiMgAlO>ZnMgAlO>FeMgAlO>CuMgAlO. No straight correlation between the H2-TPR reducibility and the catalytic performances of the samples was found in the oxidative dehydrogenation of propane into propene. The effects of the contact time and of the propane-to-oxygen molar ratio on the catalytic performances of the most active CoMgAlO, MnMgAlO and NiMgAlO mixed oxides have been investigated. [Copyright &y& Elsevier]

Abstract: Carbon dioxide methanation was carried out over a series of Ni–Ce x Zr1−x O2 catalysts prepared by a pseudo sol–gel method. The influence of CeO2/ZrO2 mass ratio and noble metal addition was investigated. The catalysts were subsequently characterized by means of XRD, TPR, BET, H2-TPD and SEM-EDX. The modification of structural and redox properties of these materials was evaluated in relation with their catalytic performances. All catalysts gave impressive CO2 conversion and extremely high selectivity to methane (superior to 98%). Ni2+ incorporation into the CZ structure was proved to enhance catalysts specific activity. The global performance of the studied systems depended not only on the surface of available metallic nickel but also on the composition of the support and on its modification by Ni2+ doping. As a result of these two phenomena, the Ni-based mixed oxide having a CeO2/ZrO2 =60/40 exhibited the highest catalytic activity, owing to an optimal Ni2+/Ni0 ratio. Noble metal addition led to higher Ni dispersion, resulting in a raise of both activity and catalyst life-time. It did not modify the support intrinsic activity. The deactivation was shown not to be due to carbon deposits but rather to nickel particles sintering. The investigated parameters thus allowed an improvement of the previously studied 5wt% Ni–Ce0.72Zr0.28O2 system. [ABSTRACT FROM AUTHOR]

Abstract: Catalysts of Pt on Fe2O3 and mixed oxides Fe x Zr(1−x)O2 were prepared for the selective CO+H2 oxidation. X-ray diffraction and Mössbauer spectroscopy showed α-Fe2O3 in pure support, a solid solution for x =0.25 and mixed oxides with segregated phases for higher “x” values. Mössbauer results showed also that with increasing the Zr content Zr4+ ions substitute the Fe3+ ions in the α-Fe2O3 lattice, and also Fe3+ ions diffusing into the zirconia lattice. The Pt/Fe0.25Zr0.75O2(p) exhibited only Fe3+ inside the ZrO2 lattice. After reduction, Fe3O4 was found in the catalysts, which decreased with increasing zirconium loading. It is interesting to note that the corresponding precursor presents 83% of Fe3+ located in the ZrO2 lattice and the remaining 17% corresponds to hematite. Catalytic tests for the preferential oxidation of CO containing H2 showed a maximum CO conversion at different temperatures after reaching total oxygen conversion. The CO conversion decreased with increasing iron content in the mixed oxide. The Pt/Fe2O3 catalyst is the most active compared to the other Pt/mixed oxide and Pt/ZrO2. Results showed the following order: Pt/Fe2O3(c)>Pt/Fe0.75Zr0.25O2(c)>Pt/Fe0.25Zr0.75O2(c)>Pt/ZrO2. The Pt/Fe0.25Zr0.75O2(c) presented high selectivity (56%) at 90°C and is 2-fold higher compared to the Pt/Fe2O3 and Pt/ZrO2 catalyst. [Copyright &y& Elsevier]

Abstract: The selective oxidation of propane to acrylic acid on MoVTeNbO x catalysts with varying concentrations of vanadium, tellurium and niobium was investigated. Catalysts containing M1 phase were obtained over the compositional range of MoV0.14–0.22Te0.1–0.2Nb0.1–0.2O x . Vanadium containing sites in the M1 phase are drastically more active for propane activation than in other materials studied. The catalytic activity is directly correlated to its fraction in the overall material and in particular the M1 phase. High concentrations of tellurium induce the formation of the M2 phase decreasing so the overall activity of the catalysts. The intrinsic activity of the M1 phase is, however, independent of the tellurium concentration. Although the presence of the M1 phase is not a stringent requirement for the oxidative dehydrogenation of propane to propene, it is required to oxidize the intermediately formed propene with high selectivity to acrylic acid. The active sites for propane activation and propene oxidation are structurally coupled, because the ratio between the rates of the two reactions was always 1:25. Oxygen defect sites in mixed oxides seem to enhance interaction with acrylic acid and lead to decarboxylation and total oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Mixed xCeO2–Al2O3 oxides with different CeO2 content (x =1–20wt%) were prepared by sol–gel method. The effect of the CeO2 content, atmosphere and temperature treatment during synthesis on the structure and properties of the xCeO2–Al2O3 was investigated. xCeO2–Al2O3 xerogels prepared from aluminum tri-sec-butoxide and Ce(III) nitrates have a pseudo boehmite-like structure. The Ce(III) ions stabilized under a reductive atmosphere randomly occupy vacant sites in tetrahedral and octahedral positions of Al2O3. The crystallization of γ-Al2O3 is suppressed and the textural properties of the mixed xCeO2–Al2O3 oxides are stabilized at high temperature. Conversely, the treatment xCeO2–Al2O3 xerogels in an oxidative atmosphere shows a progressive oxidation of Ce(III) to Ce(IV) with crystallization of γ-Al2O3 and formation of CeO2 with fluorite-like structure as the temperature rises. The effect of CeO2 on the catalytic performance xCeO2–Al2O3-supported Pt catalysts in partial oxidation of methane reaction was tested. The Pt catalysts were obtained by two methods: (i) impregnation of the xCeO2–Al2O3 supports with H2PtCl6·6H2O and (ii) one-step preparation by addition of Pt precursor during the sol–gel synthesis. CeO2-containing catalysts showed higher stability than Pt/Al2O3 catalyst obtained by impregnation method. The effect of the support was less evident when the catalysts were obtained by the one-step method. Pt catalysts based on sol–gel oxides preparation show higher thermal stability and result in higher Pt sintering resistance than conventional ones. [Copyright &y& Elsevier]

Abstract: Vapor phase condensation reactions of propanal were investigated over Ce x Zr1−x O2 mixed oxides as a model reaction to produce gasoline range molecules from short aldehydes found in bio-oil mixtures. Several operating parameters were investigated. These included the type of carrier gas used (H2 or He) and the incorporation of acids and water in the feed. Propanal is converted to higher carbon chain oxygenates on Ce x Zr1−x O2 by two pathways, aldol condensation and ketonization. The major products of these condensation reactions include 3-pentanone, 2-methyl-2-pentenal, 2-methylpentanal, 3-heptanone and 4-methyl-3-heptanone. It is proposed that the primary intermediate for the ketonization path is a surface carboxylate. The presence of acids in the feed inhibits the aldol condensation pathway by competitive adsorption that reduces the aldehyde conversion. Water also promotes ketonization and inhibits aldol condensation by increasing the concentration of surface hydroxyl groups that enhance the formation of surface carboxylates with the aldehyde. Hydrogen enhances cracking and production of light oxygenates and hydrocarbons. The light oxygenates may in turn be reincorporated into the reaction path, giving secondary products. However, the hydrocarbons do not react further. Analysis of the fresh and spent catalysts by XPS showed varying degrees of reduction of the oxide under different operating conditions that were consistent with the reaction results. Changing the proportion of the parent oxides showed that increased Zr favored formation of aldol products while increased Ce favored ketonization. This occurs by shifting the balance of the acid–base properties of the active sites. [ABSTRACT FROM AUTHOR]

Abstract: We prepared non-stoichiometric oxides based on CuO, CeO2 and ZrO2 and determined main structural properties that were tested in the partial oxidation of methane (POM). XRD results indicate that Cu is finely dispersed. It indicates the presence of a Cu x Ce y O z phase or a solid solution. In situ XRD of the CuCe sample at different temperatures and reduction conditions was obtained to verify the influence of pretreatment. For the CuCe and ZrO2 samples the conversion of methane increases with temperature, reaching maximum conversion at 850°C, which are close to the equilibrium values, On the other hand, the conversion for the CuZr is much lower. The ethylene selectivity increases above 700°C for CuCe and ZrO2 and reached 92% at 850°C on the CuCe and 83% at 800°C on the ZrO2 and on opposite, low ethylene selectivity for the CuZr catalyst. Both CuCe and ZrO2 are excellent catalysts for ethylene production but less important for H2 production in the partial oxidation of methane. Redox properties of CeO2 and the presence of Cu in the CuCe catalyst favor the formation of Ce ions that may be responsible for the oxygen migration to the molecular methane and formation of CH− radicals. The H2 selectivity is approximately close to the equilibrium value between 500 and 700°C for CuCe and CuZr catalysts. No hydrogen was formed over ZrO2. Ethylene is formed above 700°C for CuCe and ZrO2 attaining 92% at 850°C on the CuCe and 83% at 800°C on the ZrO2 and in opposite to H2, low ethylene formation on the CuZr catalyst. [Copyright &y& Elsevier]

Abstract: The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxide SiO2–WO3 using a non-hydrolytic sol–gel route. The catalyst and oxide matrix were characterized by complementary techniques (Rutherford backscattering spectrometry, ultraviolet–visible diffuse reflectance and infrared transmission spectroscopy, differential pulse voltammetry, adsorption–desorption of N2, and X-ray diffraction). The catalyst performance in terms of catalytic activity and polymer properties was evaluated by ethylene polymerization. Catalyst characterization suggested that the entrapped complex exhibited lower Zr electronic density than the corresponding unsupported metallocene. The polymerization results also revealed that this low Zr electronic density is optimized in terms of complex activation with low MAO concentration (low [Al/Zr] ratio) and reactivity. This fine tuning results in a catalyst system that is active with a low [Al/Zr] ratio and that achieves high catalytic activity. The results demonstrate that the entrapping method allows the generation of a catalyst system in which part of the activation process is attributed to the support. In this sense, the support may partially play MAO functions by stabilizing the active catalytic species. [Copyright &y& Elsevier]

Abstract: Ni–Ce0.72Zr0.28O2 catalysts containing up to 15wt% Ni were prepared, characterized and their catalytic activity was investigated in carbon dioxide methanation. The impact of the pre-treatment and the gas hourly space velocity were also studied. NiO dispersion and part of its incorporation into the mixed oxide lattice obviously increased the activity and stability of the catalysts. Very high CO2 conversions were achieved at 350 and 400°C, together with extremely high selectivity to methane (>98%) for all catalysts. Finally, high stability on stream toward deactivation was observed up to 150h at 350°C. 10wt%Ni–Ce0.72Zr0.28O2 was found to be the optimal catalyst. [Copyright &y& Elsevier]

Abstract: In this work binary and ternary mixed oxides containing Nb, V, Mo and Sb were prepared by a modified hydrolytic sol–gel technique and tested as catalysts for the selective oxidation of propane. All systems were active in the ODH of propane, with the appearance in some cases of oxygenated products. The best results as concerns the selectivity to acrylic acid (about 20%) have been obtained on ternary Mo–Nb–V oxide systems in the presence of Nb–Mo–O and V–Mo–O crystalline phases. [Copyright &y& Elsevier]

Abstract: CrCuMg layered double hydroxides (LDH) with hydrotalcite-like structure containing different proportions of Mg2+, Cu2+ and Cr3+ cations have been prepared. Thermogravimetry and X-ray diffraction data indicate that the transformation of LDH into mixed oxides is effective after calcination at 450°C. The effect of copper and magnesium for the dehydrogenation reaction of isoamyl alcohol has been examined and high conversions and selectivities to isovaleraldehyde were observed. Experimental data show that the copper is the active specie but the addition of magnesium improves the stability of the catalyst. An exhaustive analysis by XPS allowed us to analyze different copper species in the catalysts. So, Cu2+ was detected as CuO and as CuCr2O4 spinel-like in calcined samples, while Cu0 and Cu2+ were found in the reduced samples, being higher the percentage of the former with the increase of the magnesium content in the sample. Chromium is as Cr3+ in an octahedral coordination in the precursors as found by diffuse reflectance, and it occupies a similar position to that of aluminium in layered double hydroxides. The LDH are poorly crystalline, but the crystallinity degree increases after calcination, as observed by XRD. Moreover, the specific surface area determined by N2 adsorption–desorption and the “memory effect” analyzed by DTA, were related to the content of magnesium. [Copyright &y& Elsevier]

Abstract: Ni–Mg–Al catalysts prepared by continuous coprecipitation were evaluated for carbon dioxide reforming of methane carried out between 500 and 700°C. The mixed oxides obtained after calcination exhibit higher surface area values and lower crystallinity. The activity results obtained with different samples demonstrated that the catalytic properties of Ni–Mg–Al catalysts are more affected by the MII/MIII ratio than the Ni/Mg ratio. For samples with constant MII/MIII ratio the best results were obtained for 5≥Ni/Mg>1 ratios. Among the thermal pretreatment effects, the reduction temperature was revealed as a strong influence on the activity and selectivity for the CO2 reforming of methane. In contrast, the catalytic properties can be considered practically independent from the calcination temperature, and the influence of this parameter is restricted to the decrease of the surface area values with the increase of the calcination temperature. [Copyright &y& Elsevier]

Abstract: The effects of various supports on the catalytic activity of Ga2O3 for the steam reforming of DME have been examined. Among the various supported Ga2O3 catalysts, Ga2O3/TiO2 showed the highest DME steam reforming activity in terms of DME conversion and H2 yield. The results from XRD, surface area and XPS indicate that the dispersion of Ga2O3 strongly depends on the catalyst support. A correlation between the XPS results and the DME steam reforming activity reveals that there is some electronic interaction between Ga2O3 and the support element. The large electronic interaction found in Ga2O3/TiO2 leads to the best catalytic performance among all the catalysts. [Copyright &y& Elsevier]

Abstract: The steam reforming of dimethyl ether (DME) was performed on Cu/Ga x Al10− x O15 and Ga x Al10− x O15 catalysts (where ‘x’ varies from 0 to 10). The presence of Ga2O3 in Al2O3 significantly affects the catalytic performance with respect to the DME conversion and the H2 yield. It was found that the activity increases with the Ga2O3 concentration for Ga x Al10− x O15. The DME steam reforming activity on Cu/Ga x Al10− x O15 showed an improvement in the stability and H2 yield as the Ga2O3 concentration increased. A correlation between the XPS results and the DME steam reforming activity for Cu/Ga x Al10− x O15 reveals that the heterogeneity of the surface is important for achieving a high H2 yield. The specific interaction between Ga2O3 and Cu plays a decisive role in the distribution of Cu, which makes Cu/Ga x Al10− x O15 active and stable for the reaction. [Copyright &y& Elsevier]

A series of three-element mixed oxides (IA)x(IIA)yAlOz was prepared by sol–gel method, adopting a multivariate experimental design strategy in order to explore in a rational way the effects of preparation parameters on textural and basic properties. The textural properties were determined from N2 adsorption/desorption isotherms, the basicity distribution by CO2 chemisorption and temperature programmed desorption. Besides, the reactivity of toluene in the side-chain alkylation with methanol was taken as a measure of the acid–basic character of these oxides. The prepared three-element mixed oxides showed good basicity (>300 μmol/g) and textural properties among the mesoporous materials. Density and strength of the basic sites of the materials were related to the synthesis parameters by applying the multivariate analysis to data modelling. For example, the presence of large amount of alkali metals, IA/Al=0.30, was related to the increased density of medium-strong basic sites. The product distribution of the model reaction confirmed the presence of weak and very strong basic sites, the former responsible of aromatic ring alkylation and the latter of styrene synthesis. [Copyright &y& Elsevier]

By means of high-throughput synthesis and screening techniques a search of new mixed metal oxide catalysts for the selective oxidation of isobutane to methacrolein has been conducted. In a first library design the oxide precursors of nine selected elements (V, Fe, Mo, Cr, Ta, Nb, Mn, Sb and Bi) have been combined by using a sol–gel recipe and the catalysts obtained have been screened for the dehydrogenation and selective/total oxidation properties. Afterwards, the most interesting combinations were studied in more detail by screening the complete triangular composition spreads. Optimal performance towards isobutene and methacrolein yield was found for Mo10V10Sb80Ox. Finally, the best catalysts were up-scaled to gram scale and tested in a continuous flow reactor unit equipped with four parallel reactors. The improved performance of the Mo10V10Sb80Ox catalyst compared to the other catalyst formulations was consistent with the measurements made in the high-throughput MS-screening setup. [Copyright &y& Elsevier]

Catalytic hydrogenation of cinnamaldehyde (CNA) was investigated over oxidic materials obtained by the calcination of Cu-Mg-Al layered double hydroxide (LDH) precursors. A series of precursors with different Cu/Mg ratios (with a constant M2+/Al3+ ratio) were prepared by coprecipitation (under low supersaturation) and heated under reductive atmosphere until 623 K in order to avoid the formation of Cu-based spinels and to reduce the copper cations. The presence of Mg noticeably enhanced the selectivity of Cu-based catalysts with respect to the hydrogenation of the carbonyl group relative to the favoured hydrogenation of the C&z.dbnd6;C bond. Moreover, the self-condensation of hydrocinnamaldehyde (HCNA) and the cross-condensation of hydrocinnamaldehyde with cinnamaldehyde were also observed especially when the basic sites of LDH structures are preponderant over hydrogenation species. Finally, all that reaction from CNA are of great interest for getting information about: (i) basic sites involved in condensation of CNA and HCNA; and (ii) active species for selective hydrogenation of CNA to cinnamyl alcohol (CNOL) which seem in strong interaction with the first ones. [Copyright &y& Elsevier]

Several palladium-tin oxide (PdO-SnO2) catalysts were prepared by the impregnation (PdO/SnO2) and co-precipitation (PdO-SnO2) methods. Among the catalysts tested, the SnO2-supported 11 wt.% PdO catalyst prepared by the impregnation method showed the highest conversion at low temperatures. The reduction and adsorption properties of PdO/SnO2 were quite different from those of PdO/Al2O3 and PdO/ZrO2. X-ray diffraction (XRD) of these catalysts revealed that 10 nm PdO particles were supported on SnO2 for the impregnated catalysts, while the co-precipitated catalysts were composed of uniform PdO-SnO2 mixed oxide particles. Even at room temperature, the PdO particles in PdO/SnO2 were easily reduced to metallic Pd and absorbed H2 with the H2/Pd weight ratio of 0.3%. In both PdO/SnO2 and PdO-SnO2 samples, adsorption of CO was significantly suppressed because of the interaction between Pd and SnO2; the metal surface area was difficult to estimate by the CO pulse technique. [Copyright &y& Elsevier]

This paper is focused on the catalytic synthesis of butanol from ethanol in a microflow reactor at a constant weight hour space velocity (4.5 h−1) and different reaction temperatures (280, 300 and 350 °C). The reaction was catalysed by Mg-Al mixed oxides (i) pure and (ii) with added transition metals such as Co, Ni, Cu, Mn and Cr (synthesis by coprecipitation). The solid materials were deeply characterised. Other products, such as ethylene, 1,1-diethoxyethane, ethyl acetate, 1-hexanol, etc. were also determined and the reaction pathway for their formation was examined. The metals Cr and Mn did not increase the catalyst activity, which was quite low (maximum 19% at 350 °C). However, the metals Co and Ni positively influenced butanol formation, while Cu positively influenced ethyl acetate formation. Moreover, ethanol conversion increased with increasing temperature, but at the same time the selectivity to butanol decreased. [Display omitted] • The Guerbet reaction (ethanol to butanol) was catalyzed by Mg-Al mixed oxides. • The transition metals (Co, Ni, Cu, Mn and Cr) were added during co-precipitation. • A number of side products was determined and the reaction scheme was suggested. • The influence of transition metals on the reaction products was described. [ABSTRACT FROM AUTHOR]

• CO oxidation was studied by in situ Raman spectroscopy on nanostructured ceria-based materials. • In situ Raman analyses during CO oxidation allowed to monitor defect sites in operando conditions. • Cycles of reduction (CO in N 2) and oxidation (pure O 2) at 400 °C allow to study the stability of defects. • Oxygen vacancies evolved from clusters to isolated ones according to the atmosphere and temperature. • The involvement of the defect sites in structural rearrangement is fostered by easily reducible dopants. Among the factors affecting ceria activity, the defectiveness plays a key role in the case of CO oxidation. In this study, its connection with the catalytic performance was investigated via in-situ Raman spectroscopy on nanostructured pure and Cu/Mn-doped ceria, monitoring the defect sites and surface species evolution during the reaction. The accumulation of polyene-like chains, formed through CO dissociative adsorption at the catalyst surface, was observed and their disappearance was related to the catalyst light-off temperature. Moreover, the doped samples exhibited a rise of the Raman bands associated to defects after the tests, consequence of the structural rearrangements occurring during CO oxidation. Indeed, in-situ Raman measurements during reduction (CO/N 2) and oxidation cycles at 400 °C evidenced the formation of oxygen vacancy clusters in reducing atmosphere, which could reorganize not only in O 2 but also upon a temperature decrease, forming isolated vacancies and then evolving in Frenkel and extrinsic oxidized dopant-containing sites when exposed to oxygen. [ABSTRACT FROM AUTHOR]