A tailored nanostructured CuO–ZnO/Al2O3 catalyst was obtained from nanocomposites via sonochemical route through core/shell assisted by reverse micelle synthesis. The as-synthesized nanocomposites ...consisted of Cu, Zn and Al domains coated by a lauric acid shell structure with controlled physicochemical properties. Combining these features, a porous CuO–ZnO/Al2O3 supported catalyst was obtained from CuZnAl@C nanocomposite, in which Cu and Zn oxide nanoparticles interacted quite strongly with alumina. In this study, a nanostructured CuO–ZnO/Al2O3 was applied to oxidize ethylbenzene in the presence of H2O2. Catalytic results further demonstrated that the nanostructured solid had ethylbenzene conversion superior to 20% and good selectivities to acetophenone, benzaldehyde and benzoic acid compared to a benchmark CuZnAl catalyst obtained by the sol-gel method.
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•Tailored CuO–ZnO/Al2O3 catalyst obtained from CuZnAl@C nanocomposite.•Simple sonochemical route via core/shell assisted by reverse micelle synthesis.•Nuclei composed of Cu and Zn domains coated by a semi-crystalline lauric acid-based shell.•Highly dispersed CuO and ZnO on alumina converting ehtylbenzene.
Surface and bulk chemical changes in a Nafion membrane as a result of room temperature ionic liquids (RTILs) incorporation were determined by X‐ray photoelectron spectroscopy (XPS) and elemental ...analysis, respectively. RTILs with different physicochemical properties were selected. Two imidazolium based RTIL‐cations (1‐octyl‐3‐methylimidazolium and 1‐butyl‐3‐methylimidazolium) were used to detect the effect of cation size on membrane modification, while the effect of the RTIL hydrophilic/hydrophobic character was also considered by choosing different anions. Angle resolved XPS measurements (ARXPS) were carried out varying the angle of analysis between 15° and 75° to get elemental information on the Nafion/RTIL‐modified membranes interactions for a deepness of around 10 nm. Moreover, changes in the RTIL‐modified membranes associated to thermal effect were also considered by analyzing the samples after their heating at 120 °C for 24 h. Agreement between both chemical techniques, bulk and destructive elemental analysis and surface and non‐destructive XPS, were obtained.
NiO and metal-promoted NiO catalysts (M-NiO, with a M/(M+Ni) atomic ratio of 0.08, with M = Nb, Sn, or La) have been prepared, tested in the oxidative dehydrogenation (ODH) of ethane, and ...characterized by means of XRD, TPR, HRTEM, Raman, XPS, and in situ XAS (using H2/He, air or C2H6/He mixtures). The selectivity to ethylene during the ODH of ethane decreases according to the following trend: Nb–NiO ≈ Sn–NiO > La–NiO > NiO, whereas the catalyst reducibility (determined by both TPR and XAS using H2/He mixtures) shows the opposite trend. However, different reducibility and catalytic behavior in the absence of oxygen (ethane/He mixtures) have been observed, especially when comparing Nb- and Sn-promoted NiO samples. These differences can be ascribed mainly to a different phase distribution of the promoter. The results presented here are discussed in terms of the nature of active and selective sites for ODH of ethane in selective and unselective catalysts, but also the role of promoters and the importance of their phase distribution.
CO2 adsorption/desorption isotherms on HTT34 for the first (squares), second (triangles) and third (circles) adsorption/desorption cycles at 25°C. Desorption branches are highlighted by empty ...symbols. Display omitted
•Four different APTES-grafted silicas have been successfully prepared with pending amino groups for CO2 capture.•TEOS was used as silicon source and trimethyl-benzene and heptanes as swelling agents and NH4F as solubility enhancer.•CO2 uptakes of 2.4mmolg−1 or 0.64molCO2 per mol N were achieved at 1bar and 25°C and anhydrous conditions.•One adsorbent could be successfully regenerated at 100°C, maintaining a constant capacity for 3 adsorption-desorption cycles.
The CO2 adsorption capacity of different APTES-grafted mesoporous silicas of SBA-15 type has been investigated and the influence of support textural properties and the role of the presence of silanol groups on the adsorption capacity are analyzed. Four adsorbents based on SBA-15 were prepared using tetraethyl orthosilicate (TEOS) as silicon source, with and without the addition of trimethyl-benzene (TMB) and n-heptane as swelling agents, and adding in some cases ammonium fluoride as a solubility enhancer. 3-(triethoxysilyl)propylamine (APTES) was then used as grafting agent by reaction with free silanol groups on the silica surface so as to provide pending amino groups for CO2 capture. The adsorption behavior for all supports was adequately described by a Freundlich model, whereas for the APTES-grafted silica, a dual-site Langmuir model was applied, which allowed us to quantify and qualify two different adsorption sites. The addition of n-heptane as swelling agent led to pore sizes beyond 10nm and improved significantly the grafting efficiency, leading to higher CO2 uptakes as compared to the starting supports. At 1bar and 25°C and anhydrous conditions, CO2 uptakes of 2.4mmolg−1 or 0.64mol CO2 per molN were achieved (which reveals a significant contribution of physisorption). This sample could be successfully regenerated at 100°C, maintaining a constant capacity for 3 adsorption–desorption cycles. At 0.15bar and 60°C, anhydrous conditions, CO2 uptake reaches 1.5mmolg−1. This value may be theoretically doubled in the presence of humidity, and there is room for further improvement if supports with the same pore size (13nm) and higher surface areas (e.g. 1000m2/g) are successfully synthesized.
High-performance hydrodesulfurization (HDS) catalysts were prepared by incipient wetness impregnation of Ni–Mo(W) and Co–Mo(W) species over siliceous MCM-41 doped with zirconium. Catalysts with W and ...Mo loadings of 20 and 11
wt%, respectively, and with a Ni or Co loading of 5
wt%, were prepared. As a reference, a nickel–tungsten catalyst supported on a commercial γ-Al
2O
3 with a 5 and 20
wt% metal loadings, respectively has also been prepared. HDS reaction of dibenzothiophene (DBT) under 3.0
MPa of total pressure and with hourly space velocity (WHSV) of 28
h
−1 was used to evaluate the activity of these sulfided catalysts. All the catalysts displayed a very good performance in the temperature range of 300–340
°C, with conversions between 49.0% and 92.6%. The Ni promoted catalysts displayed better performances than those of Co promoted catalysts in the HDS of DBT. On the other hand they show different selectivity to hydrogenation, thus, in Ni promoted catalysts, the hydrogenation (HYD) reaction contributes more to the conversion of DBT than Co promoted catalysts where the direct desulfurization (DDS) reaction is more important. The performance of this set of catalysts is similar to that observed with a Ni5W20–Al
2O
3 catalyst in the same range of temperature (300–340
°C). However, the selectivity to the HYD product, CHB, observed with nickel promoted catalysts (Ni5–Mo11 and Ni5–W20) is higher than that found for Ni5W20–Al
2O
3 catalyst probably due to a higher superficial area of the MCM-support and to the presence on the surface of zirconium species, which leading to a better dispersion and lower stacking of the active phases.
A series of Al-containing SBA-15 type materials with different Si/Al ratio, were prepared by post-synthesis modification of a pure highly ordered mesoporous silica SBA-15 obtained by using sodium ...silicate as silica source, and amphiphilic block copolymer as structure-directing agent. A high level of aluminum incorporation was achieved, reaching an Si/Al ratio of up to 5.5, without any significant loss in the textural properties of SBA-15. These materials were fully characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),
27Al NMR spectroscopy, and N
2 adsorption at 77
K. The acid properties of these materials have been evaluated by NH
3-TPD, adsorption of pyridine and deuterated acetonitrile coupled to FTIR spectroscopy. The effective acidity of these materials was evaluated using two catalytic reactions: 2-propanol dehydrogenation and 1-butene isomerization. The adsorption of basic probe molecules and the catalytic behavior revealed an evolution of the acid properties with the Al content. These studies have shown that the Al-SBA-15 materials contain Brønsted and Lewis acid sites with medium acidity which makes them appropriate to be used as acid catalysts in heterogeneous catalysis, catalytic supports, and adsorbents.
Al KLL spectra of Al-SBA-15 materials with different Si/Al ratios.
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•Iron phosphide based catalysts presenting different stoichiometry were prepared.•Fe2P phase is more active than FeP one in the HDO of phenol.•Cyclohexane and cyclohexene were the ...main products for all studied catalysts.•The presence of different iron phosphides in the catalysts was detrimental in the catalytic activity.•TOF is related to iron surface exposure, particle size and catalyst acidity.
Iron phosphide catalysts supported on silica with an iron loading of 15 wt% were synthesized and studied in the hydrodeoxygenation (HDO) of phenol. The amount of phosphorus varied in order to obtain iron phosphides with different stoichiometry. Catalysts containing Fe2P, FeP and FeP2 phases were obtained. The textural and structural properties of the prepared catalysts were evaluated by using different experimental techniques such as N2 adsorption-desorption at -196 °C, X-ray diffraction (XRD), Mössbauer spectroscopy, high resolution transmission spectroscopy (HRTEM), infrared spectroscopy (IR) of adsorbed CO at low temperature, X-ray photoelectron microscopy (XPS) and NH3 thermoprogrammed desorption (NH3-TPD). The catalytic activity was studied at 275 °C and at 15 and 5 bar of hydrogen pressure in the hydrodeoxygenation reaction of phenol. Characterization results evidenced that the initial P/Fe ratio employed in the synthesis not only governed the stoichiometry of the iron phosphide, but also the particle size, metallic surface exposure and acidity. The catalysts presenting unique phases were those presenting better activity in the HDO reaction of phenol. Moreover, Fe2P phase presented better results than FeP in terms of HDO conversion.
MgO-La2O3 catalysts with different Mg/La molar ratio were synthesized by a precipitation method and a subsequent calcination and then characterized by x-ray diffraction, N2 adsorption-desorption ...isotherms (at −196 °C), CO2- and NH3-thermoprogrammed desorption and x-ray photoelectronic spectroscopy. The coexistence of acid and basic sites promoted the selective transformation of ethanol into valuable products. Thus, MgO catalyst promoted the Guerbet reaction obtaining n-butanol as product while the incorporation of La2O3 in the catalytic system improved the ethanol conversion notably, obtaining ethylene as the main product due to a dehydration reaction. The highest ethylene yield was obtained for the catalyst with a Mg/La molar ratio of 1.
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•The coexistence of acid and basic sites promotes the selective transformation of ethanol.•MgO catalyst promotes the Guerbet reaction obtaining n-butanol as main product.•The presence of La2O3 in Mg-La-O catalysts improves the ethanol conversion to ethylene.•The highest ethylene yield was obtained for the catalyst with a Mg/La molar ratio of 1.
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•Separation of volatile hydrocarbons by Cu-BTC and FE-BTC.•Metal-organic frameworks for volatile hydrocarbons separation.•Effect of structural factors in Cu-BTC and Fe-BTC surface ...properties.
The separation of alkanes (nC5 to nC9), propane and propylene, and aromatic (benzene, toluene and o-xylene) hydrocarbons using the metal-organic frameworks Cu-BTC and Fe-BTC as stationary phase was evaluated from inverse gas chromatography data. Both materials were found able to separate mixtures of these volatile hydrocarbons. The nature of such behavior is discussed according to the possible guest-host interactions during the molecules adsorption and retention in the column and considering the molecules size and shape and the porous framework topology. From the recorded chromatographic profiles, the retention times for the considered hydrocarbons were calculated and then used to obtain the involved differential adsorption heats and the values for the separation coefficient. Cu-BTC is a long-range ordered crystalline material while Fe-BTC shows gel-like features. Such structural differences modulate the pore accessibility and the adsorption interactions. In this contribution, the effects of these structural differences on the molecules adsorption and separation are discussed. From the recorded adsorption data, information on the pore volume, adsorption potentials and probable pore topology for Fe-BTC was obtained.
Highly sodium deficient Na0.6NbO3 (NN) ceramics were prepared and characterized. Their mean structure could be described by a mixture of the predominant P polymorph (S.G. Pbma) and the Q phase (S.G. ...P21ma), at room temperature, as deduced from Rietveld refinements of Powder X-ray diffraction and Raman scattering data. Besides, microstructural and compositional heterogeneity was evidenced from HRTEM and XPS analyses. Dielectric measurements on this highly vacancies-containing NN material indicated a hysteretic transition taking place at ~12 and −18 °C on the heating and cooling regimes, respectively. This means a considerable shift to lower temperatures of the transition temperatures concerning the P/Q transformations previously described for the NaNbO3 material. At an intermediate frequency of 10 kHz, maximum permittivity and tangent loss values of ε' = 1250 and tgδ = 2 were obtained on heating, whereas lower values of ε' = 65 and tgδ = 0.04 were displayed on cooling regime. These anomalies were interpreted in terms of ferrolectric-antiferroelectric-paralectric phase-transitions implying a PTCR behavior within certain temperature range. This response, observed in this complex material for the first time, has interesting implications for the possible application of NN ceramics in sensing and dielectric materials fields.
