A new approach has been tested for the preparation of metal/Mo
2
C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to ...study the reduction and carburization processes of Cu
3
(MoO
4
)
2
(OH)
2
, α-NiMoO
4
and CoMoO
4
·
n
H
2
O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo
2
C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu
2+
, Ni
2+
and Co
2+
cations inside each molybdate. The synthesized Cu/Mo
2
C, Ni/Mo
2
C and Co/Mo
2
C catalysts were highly active for the hydrogenation of CO
2
. The metal/Mo
2
C systems exhibited large variations in the selectivity towards methanol, methane and C
n
H
2n+2
(n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C–O bonds. Cu/Mo
2
C displayed a high selectivity for CO and methanol production. Ni/Mo
2
C and Co/Mo
2
C were the most active catalysts for the activation and full decomposition of CO
2
, showing high selectivity for the production of methane (Ni case) and C
n
H
2n+2
(n > 2) hydrocarbons (Co case).
Graphical Abstract
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► Supporting the heteropolyacids increased the catalytic activities. ► Surface acidity and calcination temperature related to HDS activity and stability. ► Catalysts presented a good ...structural and morphological stability during reaction.
A series of tungsten and molybdenum catalysts supported on MCM-41 were prepared using Keggin heteropolyacids (H3PM12O40, M=Mo or W) as active phase sources and compared with their analogues unsupported. The physicochemical characterization was carried out by, small angle and wide angle X-ray diffraction; thermogravimetric analysis/differential scanning calorimetry; ultraviolet–visible diffuse reflectance and Fourier transform infrared spectroscopies; N2 physisorption and potentiometric titration with N-butylamine, for determination, respectively, of the structure; thermal stabilities; integrity of heteropolyacids; textural properties and superficial acidity. The solids were tested in the thiophene hydrodesulfurization reaction at 400°C, atmospheric pressure and weight hourly space velocity of 0.48h−1. In this study, it has been demonstrated the importance of supporting heteropolyacids to increase the catalytic activity. Furthermore, it was proved a correlation between surface acidity and calcination temperature with the activity and stability of these catalysts in the hydrodesulfurization reaction.
•Catalysts with (Ni/(Ni + W) = 0.50 had the highest activity in thiophene HDS.•NiW carbide and nitride has potential for pollutant reduction in an extra-heavy feedstock.•HDN results of these ...materials were less promising.•NiW catalysts changed the chemical nature of crude oil and asphaltenes.
Alumina-supported Ni-promoted W oxides, carbides and nitrides were presulfided and employed for reducing pollutants and increasing the quality of an extra-heavy crude oil during catalytic upgrading reactions. These materials were prepared by temperature programmed reaction using reactive gases and varying the (Ni/(Ni + W)) atomic ratio from 0.00 to 1.00. Catalysts were characterized by XRD, SEM, HRTEM and N2 physisorption. In order to study the effect of the atomic ratio in the conversion of the model molecule thiophene, room pressure HDS tests were used. The catalysts with best performances during thiophene HDS were tested in the upgrading of a Venezuelan extra-heavy crude oil characterized by having high asphaltenes, S and N contents, affecting competitiveness in the global market. These results were compared with a commercial NiMo catalyst. API gravity of crude oil, CHNS elemental analysis, 13C- and 1H NMR of crude oil and asphaltenic fraction, in addition to flocculation threshold of asphaltenes, were studied in order to verify variations in physicochemical properties of oil due to catalytic upgrading and to seek evidence of pollutants reduction and improvement of quality during this process. NiW catalysts with atomic ratio (Ni/(Ni + W) = 0.50 showed remarkable performance during thiophene HDS and heavy oil hydrotreatment, improving API gravity and reducing S content, modifying chemical nature of crude oil and asphaltenes, as it was revealed by results of elemental analysis, H/C ratio, flocculation threshold, Caro/Cali and Haro/Hali ratios. However, no significant variations were found in N contents of crudes and asphaltenes revealing poor HDN performance, apparently due to Na traces from the W precursor remaining in the final NiW catalysts.
The microstructural effects on the corrosion resistance of an API 5L X42 carbon steel in 0.5 M NaCl solution saturated with CO2 was investigated. Four microstructures were considered: banded (B), ...normalized (N), quenched and tempered (Q&T), and annealed (A). Electrochemical measurements (polarization curves and electrochemical impedance spectroscopy) were coupled with surface analyses (scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS)) to characterize the formation of the corrosion product layers. Electrochemical results revealed that corrosion resistance increased in the following order: B < N < Q&T < A. From the polarization curves it was shown that specifically, cathodic current densities were affected by microstructural changes. SEM images indicated that ferrite dissolved earlier than cementite and a thin layer of corrosion products was deposited on the steel surface. XPS analyses revealed that this layer was composed of a mixture of iron carbonate and non-dissolved cementite. It was also found that the quantity of FeCO3 content on the steel surface was greater for Q&T and A microstructures. These results, in agreement with the electrochemical data, indicate that the deposition mechanism of iron carbonate is closely related to the morphology of the non-dissolved cementite, determining the protective properties of the corrosion product layers.
•The effect of change in microstructure on CO2 corrosion resistance was evaluated.•An API 5LX 42 carbon steel was immersed in a 0.5 M NaCl solution saturated with CO2.•Banded, normalized, quenched-tempered and annealed microstructures were considered.•Electrochemical measurements were coupled with surface analysis.•Morphology and distribution of undissolved Fe3C control corrosion kinetics.
The present study evaluates the feasibility of partially dealuminated natural mordenite as a catalyst support by studying improvement in its textural properties. This is the first study that reports ...the dealumination of natural zeolite-based tuffs from Ecuador. For this purpose, mordenite-rich tuffs were obtained from deposits close to Guayaquil, Ecuador. The raw material was micronized in order to increase its surface, and treated with NH4Cl. NH4+ cation-exchanged samples were finally reacted with HCl(aq) to complete the dealumination process. The partially dealuminated samples were characterized using techniques such as XRD, FT-IR, SEM-EDS, and identification of their textural properties. Dealumination with HCl(aq) increased the Si/Al ratio up to 9 and kept the crystallographic structure of natural mordenite, as XRD results showed that the structure of mordenite was not altered after the dealumination process. On the other hand, textural properties such as surface area and microporosity were improved as compared to natural mordenite. In view of these results, the feasibility of using natural mordenite as a catalyst support is discussed in this study.
A mesoporous titania material with a single X-ray diffraction signal at small-angle and anatase TiO
2
walls was prepared by a sol–gel method using hexadecylamine as a templating agent and titanium ...isopropoxide as a titanium precursor. The mesoporous solid was used to prepare a novel layered titanium phosphate by Soxhlet extraction reflux with phosphoric acid. The obtained α-TiP material showed a typical wide-angle X-ray diffraction pattern with a monoclinic structure, N
2
adsorption–desorption isotherms Type II, and large crystals of rectangular lamellae, confirming its layered nature by transmission electron microscopy. The elimination by adsorption of Hg
2+
ions from aqueous samples was studied using Langmuir, Freundlich and Temkin models, calculating its different parameters. The adsorption of Hg
2+
ions could be performed via active P-OH groups (observed by Fourier Transform Infrared results) in the lamellar structure showing excellent properties that make the layered material possible excellent adsorbent to remove heavy metals ions contaminants from potable water.
Highlights
The synthesis of a novel layered titanium phosphate has been studied.
A mesoporous titania prepared by sol–gel method was used as titanium source.
The successful formation of the layered titanium phosphate in the alpha phase was confirmed by several characterization techniques.
The adsorption experimental data for Hg
2+
uptake from aqueous solutions were analyzed using the Langmuir, Freundlich, and Temkin models.
The results propose the material might be an efficient adsorbent for wastewater treatment and water purification.
Pechini sol–gel method has been employed for the preparation of nanocrystalline La0.8Sr0.2FeO3 perovskite. The synthesis procedure was optimized by varying the calcination temperature. The results ...revealed the decomposition of the resin precursor and confirmed the formation of the perovskite phase starting at 600°C with spherical morphology (<50nm) and subsequently increased crystal size at higher temperatures, in all cases with a structure consisting of agglomerates. The presence of pores formed by the combustion of the resin precursor was appreciable in perovskites obtained at 600 and 850°C, whereas sintering was observed at 1000°C.
•La0.8Sr0.2FeO3 nanocrystals are synthesized via Pechini sol–gel method.•Perovskite phase formation starts at low temperature.•Effect of thermal treatment upon structure, particle size, porosity and morphology.
•DFT calculated interactions of Mo species on a pyrolytic graphite platform.•Calculations shed some lights on Mo adsorbed species during the ETAAS processes.•Molybdenum oxide species strongly bonded ...to pyrolytic graphite edges.•Mo adsorbs tightly on dehydrogenated and decarbonized sites of graphite surface.•Correspondence between adsorption energies of Mo species and XPS data.
Adsorptions of molybdenum species and interactions on a model pyrolytic graphite platform (PGP) sites were calculated employing quantum methods (density functional theory (DFT) and parametric method number 6 (PM6)). The aim of this work is to propose, at the molecular level, the structure of different chemisorbed species on the PGP surface used in the electrothermal atomic absorption spectroscopy (ETAAS) process for a Mo analyte. The carbon surface was modeled by a seven-ring polycyclic aromatic system (coronene). Molybdenum species (Mo, Mo2, MoO, MoO2, MoO3, and MoO4) adsorbed on a coronene surface were studied on different adsorption sites. Calculations of these species showed that chemisorption strengths are stronger on dehydrogenated and decarbonized edge sites than on sites located in the flat central region of the model graphite. It was confirmed that Mo-oxygenated species interactions are very strong at the edge sites and therefore the reduction of these species must occur before the atomization (evaporation of Mo species) takes place, in agreement with experimental results. Comparisons between experimental XPS spectra for ETAAS process (drying, ashing, and atomization) and calculated adsorption energies of Mo species allow an interpretation of which species are present on the PGP at each stage. The presence of very strong bonded molybdenum carbide species on decarbonized sites may explain the memory effects. Experimentally observed migration of Mo oxide species to the edges of the PGP is also corroborated by their small chemisorption energies on central sites of the PGP model.
Display omitted High-resolution XPS spectra of Mo 3d signal in different PGP regions. Temperature treatment: 600 °C. Regions of PGP are shown in inset: (A) central region, (B) left border and (C) right border. Schematic representation of Mo species reduction (MoO4 → MoO3) on two adjacent E2 sites of the graphitic surface. The value of ΔEreact was evaluated with DFT calculations.
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•1,3-butadiene hydrogenation performance on structured substrate have been studied.•Foams present better performance than monoliths due to better mass transfer.•Catalysts thickness ...influence directly selectivity producing undesired products.•The mass transfer of reactants to the catalyst layer surface plays a major role.
Different aluminium structured substrates (monoliths of 350 and 1100cpsi; foams of 10, 20 and 40ppi) have been loaded with NiPd/(CeO2-Al2O3) catalyst by washcoating. To improve the adherence between catalyst particles and metallic surface, aluminium substrates were previously anodized to produce a rough (cracked) surface. Catalytic layers of different thickness have been deposited onto aluminium substrates. The catalytic coatings were characterized measuring their textural properties, adhesion and morphology. These structured catalysts have been tested in the selective hydrogenation of 1,3-butadiene in presence of 1-butene under liquid-phase conditions. The effects of some design parameters over the catalytic performance were studied: catalyst loading (125, 250 or 500mg), geometry of the structured substrate (monoliths or foams), and porosity (cpsi or ppi). The catalytic results show that foams present better activity than the monoliths. This can be related to better mass and heat transfer in the case of foams. In addition, the catalytic coating thickness influence directly the reaction selectivity; thicker layers produce undesired products (BA and isomers) due to diffusion limitations. However, it seems that the mass transfer of reactants to the surface of the catalyst layer plays a major role than the diffusion of reactants inside the catalyst layer.
Hexagonal mesoporous MCM-41-type molecular sieve has been functionalized with (3-mercaptopropyl)trimethoxysilane and used to heterogenize two large Co(II)- and Cu(II)-complexes containing a ...terpyridine-based Schiff base macrocyclic ligand. First, thiol groups were linked to the siliceous surface of the mesoporous host via grafting process. Some samples were characterized by FTIR, ICP-AES, SA-XRD, N2 physisorption, 13C-MAS-NMR, XPS and EPR. This set of characterization techniques confirmed a successful functionalization process, and also confirmed that the used experimental procedure allowed the heterogenization of Co(II)- and Cu(II)-complexes inside the pores of the functionalized host, retaining the mesoporous structure. The homo- and heterogeneous catalysts were active for cyclopentene oxidation. Co@MCM(F) sample was reported in this article as the best catalyst due to its higher activity and selectivity, as well as its low loss of catalytic activity after reuse.
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•The synthesis and functionalization of MCM-41-type silica mesoporous material with has been studied.•The immobilization of two large Co(II)- and Cu(II)-complexes was successful carried out.•Both homo- and heterogeneous catalysts were active for cyclopentene oxidation.•The heterogenized catalysts presented a higher activity and good recoverability during two consecutive reactions.
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