Showing papers on "Mixed oxide published in 2019"
TL;DR: In this paper, a detailed knowledge of long-term deactivation of Ni catalysts in CO2 methanation was provided, where Ni particle growth and a decrease in the BET surface area lead to deactivation.
Abstract: This work provides detailed knowledge of long-term deactivation of Ni catalysts in CO2 methanation. NiAlOx mixed oxides with varying Ni loading as well as a 17 wt-% Ni/γ-Al2O3 catalyst were synthesized via co-precipitation and incipient wetness impregnation, respectively. The catalysts were aged at 523, 573 and 623 K under equilibrium conditions up to 165 h. Periodic activity measurements under differential conditions reveal severe deactivation. The stability of co-precipitated systems increases with decreasing Ni content on the expense of catalyst activity. Ni/γ-Al2O3 exhibits a lower stability as a comparable mixed oxide. A power law model is applied for the kinetic description of deactivation. Catalyst samples are characterized by means of temperature programmed desorption of H2 (H2-TPD) and CO2 (CO2-TPD), pulsed H2 chemisorption, XRD, FT-IR spectroscopy, XPS and N2 physisorption. Main deactivation mechanisms in the co-precipitated samples are found to be Ni particle sintering, a loss of BET surface area as well as a reduction of CO2 adsorption capacity and medium basic sites, along with structural changes of the mixed oxide phase. Ni particle growth and a decrease in BET surface area lead to deactivation of the impregnated sample. Structure-activity correlations imply a complex interplay of governing deactivation phenomena as well as structure sensitivity.
75 citations
TL;DR: It is demonstrated that the solid precursor calcined at 300 °C exhibited the best catalytic ozonation activity with respect to CuAl2O4 spinel phase obtained at higher temperatures, and proposed that such catalytic performance was related to a synergistic function between ≡Cu2+ and ≡Al3+, which took part of a mechanism of radical formation.
71 citations
TL;DR: A hydrothermal synthesis method is shown that generates M1 phases with high surface areas starting from poorly soluble metal oxides, thus exposing a large concentration of active sites in ethane oxidative dehydrogenation to ethene.
Abstract: Ethane oxidative dehydrogenation (ODH) is an alternative route for ethene production. Crystalline M1 phase of Mo-V mixed metal oxide is an excellent catalyst for this reaction. Here we show a hydrothermal synthesis method that generates M1 phases with high surface areas starting from poorly soluble metal oxides. Use of organic additives allows control of the concentration of metals in aqueous suspension. Reactions leading to crystalline M1 take place at 190 °C, i.e., approximately 400 °C lower than under current synthesis conditions. The evolution of solvated polyoxometalate ions and crystalline phases in the solid is monitored by spectroscopies. Catalysts prepared by this route show higher ODH activity compared to conventionally prepared catalysts. The higher activity is due not only to the high specific surface area but also to the corrugated lateral termination of the M1 crystals, as seen by atomic resolution electron microscopy, exposing a high concentration of catalytically active sites. Crystalline M1 phase of Mo-V-Te-Nb mixed oxide is an excellent catalyst for ethane oxidative dehydrogenation to ethene. Here, the authors show a method that synthesizes highly active materials by generating M1 crystals with corrugated terminations, thus exposing a large concentration of active sites.
66 citations
TL;DR: In this article, Ni-based catalysts supported on CeO2-MgO mixed oxides (0.20% CeO 2 molar content) were prepared and employed in DRM.
Abstract: Dry reforming of methane (DRM) is becoming an appealing research topic because of the urgent need to minimize global warming and the demand for alternative energy resources. However, DRM commercialization and industrial scale application are limited by the deactivation of the applied catalysts. In this work, Ni-based catalysts supported on CeO2–MgO mixed oxides (0–20% CeO2 molar content) were prepared and employed in DRM. The support was synthesized via a coprecipitation method followed by impregnation of Ni metal. The catalysts prepared were characterized by X-ray diffraction, Brunauer–Emmett–Teller (BET) analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy (FESEM) techniques. The catalytic performance of the catalysts was evaluated in a fixed-bed continuous reactor with an equimolar (CH4/CO2) ratio at 1073 K. The addition of CeO2, as a promoter to the support, altered the interaction between Ni and MgO and modulated the properties ...
63 citations
TL;DR: In this article, the acid-base properties of AMO-LDH-based oxide catalysts with various ratios of Mg/Al were studied for the chemical and physical properties and the activity on esterification of benzoic acid with 2-ethylhexanol.
Abstract: Proven to possess distinguishable physical and acid-base properties superior to conventional LDHs, Aqueous Miscible Organic solvent-Layered Double Hydroxides (AMO-LDHs) were thus synthesized and used as precursors to prepare the Mg/Al mixed oxide catalysts in this work. The AMO-LDH based oxide catalysts with various ratios of Mg/Al were studied for the chemical and physical properties and the activity on esterification of benzoic acid with 2-ethylhexanol. The catalysts were characterized using BET, XRD, TGA, and XPS. Moreover, the acid-base properties were studied by using NH3-TPD, CO2-TPD, and X-ray Absorption Spectroscopy (XAS) techniques, both XANES and EXAFS. As a result, the Mg/Al mixed oxides after calcination at 500 °C still had the clay structure, and were found to possess both acid and base sites. As the Mg/Al ratio increased, the total density of acid and basic sites decreased. Moreover, the acid-basic strength depended on their phase compositions and coordination number. The activity of calcined LDHs catalysts was tested for the esterification of benzoic acid with 2-ethylhexanol, aimed at producing 2-ethylhexyl benzoate as the desired chemical. The products were analyzed using GC–MS/TOF. In summary, the conversion of benzoic acid was enhanced significantly using the Mg Al mixed oxides as the catalysts, owing to the acid-base sites (both Mg2+ O2− and Al3+ O2− pairs) of the catalysts. The catalyst with the Mg/Al ratio of 4:1 can convert 66% benzoic acid to 2-ethylhexyl benzoate. Moreover, the other products were composed of 2-ethylhexanal, 3-heptanone, and 3-heptanol because of acid-base pairs.
61 citations
TL;DR: In this article, the authors demonstrate the use of surface phase oxide in the form of MgAl mixed oxide nanosheets for reforming of methane contained in biogas, using CO2 as an oxidizer, to make syngas (H2 and CO).
Abstract: For many reactions balancing the degree of interaction between the metal catalyst and the underlying support material is pivotal for obtaining optimal catalytic performance. One important example is the reforming of methane contained in biogas, using CO2 as an oxidizer, to make syngas (H2 and CO). For this reaction to become industrially viable, the catalyst needs to be based on non-precious transition metals. Unfortunately, catalyst deactivation induced by metal sintering and coking remains a major challenge for this class of catalysts. Herein, we demonstrate the use of a ″surface phase oxide″ in the form of MgAl mixed oxide nanosheets (
60 citations
TL;DR: In this article, the visible light irradiated photocatalytic degradation of diclofenac using ZnO-WO3 mixed oxide catalysts, prepared by the hydrothermal method with variation in molar ratios of tungsten precursor.
Abstract: Diclofenac is known to be a persistent pharmaceutical compound, and their effective removal from water sources has been a rising concern. This study reports the visible light irradiated photocatalytic degradation of diclofenac using ZnO-WO3 mixed oxide catalysts, prepared by the hydrothermal method with variation in molar ratios of tungsten precursor. The prepared catalysts were characterized using a different technique, and the photocatalytic activity has been tested under visible light irradiation. Adsorption isotherm studies were performed to elucidate the preferential adsorption nature of the mixed oxide catalyst. The interaction of diclofenac and the prepared mixed oxides is based on the positively charged ZnO-WO3 surface and anionic diclofenac at solution pH 6. The adsorption and photodegradation kinetics is best expressed by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. Results indicated that all the prepared catalysts exhibited better catalytic activity than the bare ZnO under the visible light irradiation. The catalyst prepared with a molar ratio of 10:1 is proven to be an efficient catalyst and achieved 76%mineralization of diclofenac during the irradiation. The effect of operating variables like pH, initial diclofenac concentration, and catalyst loading was investigated and reported. The ZnO-WO3 mixed oxide catalysts were showed better stability, and the results revealed that the photocatalytic efficiency was retained up to 80% over the repeated reaction cycles. Several intermediate compounds formed during the photocatalytic reaction have been analyzed using LC–MS, and their degradation pathways have been found to primarily follows hydroxylation, dechlorination and decarboxylation reactions.
58 citations
TL;DR: Mn3AlO mixed oxide catalysts derived from MnxAl-LDHs were prepared and tested for acetone catalytic oxidation as discussed by the authors, and the results indicated that the surface intrinsic and formed oxygen vacancies can induce the Mn-O bond of structural unit [MnO6] weakened.
Abstract: MnxAlO mixed oxide catalysts derived from MnxAl-LDHs were prepared and tested for acetone catalytic oxidation. Detailed results indicated that the surface intrinsic and formed oxygen vacancies can induce the Mn-O bond of structural unit [MnO6] weakened. Subsequently, it can improve the redox properties of catalysts, and enhance the capacity of gaseous oxygen species dissociation and adsorption. Among them, Mn3AlO catalyst displayed the best catalytic performance for acetone oxidation (T90 = 164 °C) with the production of low amount of byproduct ( 99%) producted. Additionally, the Mn3AlO catalyst can proceed consecutively for 12 h reaction without notable deactivation. Furthermore, in situ DRIFT and theoretical calculations methods was adopted to explore the reaction mechanism. And η1(O)(ads) (adsorption mode of acetone), CH2=C(CH3)=O(ads), O*, CH3CHO*, CH2O* and COO(ads) were considered as the main intermediate species and/or transient state during the reaction process. It was revealed that the acetone and oxygen molecules were activated by the dehydrogenation (α-H abstraction) and dissociation process over Mn3AlO catalyst, respectively, and then the intermediate specie, CH2 C(CH3) O and O*, were produced, which was followed by the breaking of C C bonds to produce the CH3CHO* and CH2O* species. Finally, these species were attacked by dissociated oxygen (O*) and therefore further dehydrogenation occurred, form H2O and CO2 via the COO adsorbed species. Particularly, C C bond breaking was the main rate determining step for acetone oxidation.
51 citations
TL;DR: In this article, a mixture of CoAl(Ce) mixed oxides was synthesized by co-precipitation and the results were characterized by several techniques: XRD, BET, H2-TPR and XPS.
Abstract: Hydrotalcite like compounds containing Co, Al and Ce were synthesized by co-precipitation. The mixed oxides obtained after calcination were characterized by several techniques: XRD, BET, H2-TPR and XPS. Activities of mixed oxides were evaluated in toluene total oxidation in presence or in absence of carbon monoxide. The benzene, benzyl alcohol and benzaldehyde are principal by-products observed during toluene oxidation in presence of CoAl(Ce) mixed oxides. Moreover, presence of carbon monoxide improves toluene total oxidation over CoAlCe mixed oxides. Stability of the two best catalytic materials has been tested in the two conditions and show no deactivation.
46 citations
TL;DR: In this paper, Co and Ni doped Fe-based catalysts, supported over γ-Al2O3 were prepared by a wet-impregnation method and evaluated for hydrogenation of CO2 to CO at temperatures range of 450-650 C and atmospheric pressure.
Abstract: Utilization of CO2 by converting it into CO via reverse water-gas shift (rWGS) reaction is of particular interest due to the direct use of CO as feedstock in many significant industrial processes. Here, Co and Ni doped Fe-based catalysts, supported over γ-Al2O3 were prepared by a wet-impregnation method and evaluated for hydrogenation of CO2 to CO at temperatures range of 450–650 °C and atmospheric pressure. The catalytic activity in rWGS reaction mainly depends on the oxide phase of the iron. It was found that introduction of Co- or Ni- in iron oxide catalyst significantly enhanced the activity as compared to the undoped Fe/Al2O3 catalyst. However, among the doped catalysts, Co-Fe/Al2O3 showed highest CO yield (48%) and stable time-on-stream performance for 40 h at 3:1 H2/CO2 feed ratio and space velocity of 1000 mL/gcat.min at 650 °C and atmospheric pressure. The better performance of Co-Fe/Al2O3 catalyst was due to the improved reducibility of iron-oxide after doping of Co- and formation of mixed oxide, which is non-selective for methane formation under the rWGS reaction conditions. The detailed characterization results on surface area, size, morphology, reducibility and thermal stability of the prepared Fe-based catalysts obtained by BET, particle size analysis, SEM, XRD, TPR, and TGA techniques were used to understand the role of dopant in enhancement of the observed catalytic activity.
45 citations
TL;DR: In this paper, a series of mesoporous nanocrystalline TiO2-Al2O3 supports containing 0 to 100% alumina were synthesized via improved evaporation-induced self-assembly (EISA) strategy.
TL;DR: In this article, a bimetallic Au-Pd catalyst supported on ceria-zirconia with Au:Pd molar ratio 0.8 was synthesized using a simultaneous deposition-precipitation method and oxidized at 250, 450, and 700°C in order to modify its particle size, nanostructure, and composition.
TL;DR: In this article, a series of 20 wt% Ni-Cu mixed oxide catalysts were prepared by co-impregnation, varying the Ni−Cu composition and showed good stability due to less coke formation.
Abstract: A series of CeO2 supported 20 wt% Ni–Cu mixed oxide catalysts was prepared by co-impregnation, varying the Ni–Cu composition. The catalysts were characterized by nitrogen adsorption for BET surface area, X-ray diffraction (XRD), Temperature programmed reduction (TPR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), H2 Chemisorption, Scanning electron microscopy (SEM) and CHNS analysis techniques. They were evaluated for dry reforming of methane to produce syngas in the temperature range of 600–800 °C and at a GHSV = 28,800 h−1. 5 wt% Ni + 15 wt% Cu/CeO2 displayed superior activity among the series. The incorporation of Ni metal in CeO2 lattice led to the formation of Ni–O–Ce solid solution up to 5 wt% Ni in the catalyst. This catalyst also showed good stability due to less coke formation. Resistance towards coking was observed to be mainly due to the abundance of labile oxygen in the solid solution.
Ni incorporation in CeO2 results in significant change in the CeO2 lattice leading to solid solution formation and enhancing metal dispersion. Increase in the oxygen storage capacity (OSC) with the addition of Cu helps improve catalyst stability.
TL;DR: In this paper, the functionality of ex-solved Ni nanoparticles can be further improved when Fe is co-exsolved with Ni, as Fe-Ni alloy nanoparticles, eventually forming mixed oxide nanoparticles.
Abstract: Metallic nanoparticles exsolved at the surface of perovskite oxides have been recently shown to unlock superior catalytic activity and durability towards various chemical reactions of practical importance. For example, for the CO oxidation reaction, exsolved Ni nanoparticles in oxidised form exhibit site activities approaching those of noble metals. This is of particular interest for the prospect of replacing noble metals with earth-abundant metal/metal oxide catalysts in the automotive exhaust control industry. Here we show that for the CO oxidation reaction, the functionality of exsolved Ni nanoparticles can be further improved when Fe is co-exsolved with Ni, as Fe–Ni alloy nanoparticles, eventually forming mixed oxide nanoparticles. As compared to the Ni nanoparticles, the alloy nanoparticles exhibit higher site activities, greatly improved durability over 170 h of continuous testing and increased tolerance towards sulphur-based atmospheres. Similarly to the single metal nanoparticles, the alloys demonstrate outstanding microstructural stability and high tolerance towards coking. These results open additional directions for tailoring the activity and durability of exsolved materials for the CO oxidation reaction and beyond.
TL;DR: In this article, supported Co3O4 and Co4MnAlOx mixed oxides were prepared by deposition on SiC open-cell foams by wet impregnation and suspension methods and characterized by AAS, BET, XRD, SEM, TEM, TPR-H2, XPS and nitrogen adsorption methods.
Abstract: Supported Co3O4 and Co4MnAlOx mixed oxides were prepared by deposition on the SiC open-cell foams by wet impregnation and suspension methods and characterized by AAS, BET, XRD, SEM, TEM, TPR-H2, XPS and nitrogen adsorption methods. Prepared supported catalysts as well as active phase Co3O4 and Co4MnAlOx in grain form prepared from parent solutions were tested for nitrous oxide decomposition. Catalytic activity of grain active phase was governed by methods of preparation; Co3O4 and Co4MnAlOx prepared by suspension method were significantly more active than those from solutions for impregnation method. Suspension method provided active phase with higher surface areas and sites with better reducibility, both of these factors contributed to higher N2O conversions. In contrast to this, N2O conversions over supported catalysts were dependent more on chemical composition of active phase than on method of preparation. Both catalysts containing Co4MnAlOx mixed oxide revealed higher conversion of N2O than catalysts containing Co3O4. STEM analysis of the most active Co4MnAlOx prepared by suspension method showed (i) segregation of Co3O4 nanocrystals of cuboctahedral shape containing (100) and (111) facets (this segregation was confirmed also by XPS and TPR-H2) and (ii) Co-Mn-Al oxide nanoparticles with very small un-faceted grains assembled into elongated fiber-like agglomerates were observed by STEM.
TL;DR: In this article, a novel P-doped Fe2O3-TiO2 mixed oxide was successfully prepared by a microwave assisted sol-gel method, which was characterized by N2 physisorption, SEM, XRD, XPS, and FTIR, UV-vis DRS, and PL spectroscopies.
TL;DR: In this paper, the authors designed a high performance denitration (De-NOx) catalyst based on a micrometer-sized spherical Mn-Ce-Fe-Ti (CP-SD) catalyst for selective catalytic reduction (SCR).
TL;DR: The perovskite-type mixed oxide La0.3Sr0.95Ni0.05O3−δ (LSTN) is demonstrated to exhibit the remarkable property of structural regeneration as discussed by the authors.
Abstract: The perovskite-type mixed oxide La0.3Sr0.55Ti0.95Ni0.05O3−δ (LSTN) is demonstrated to exhibit the remarkable property of structural regeneration, where Ni can be reversibly exsoluted from the host perovskite lattice resulting in a regenerable Ni catalyst for solid oxide fuel cell anode applications. Results of catalytic tests for the water gas shift reaction and electrochemical investigations on a button-sized fuel cell demonstrate the redox stability of LSTN, its potential application in solid oxide fuel cells, and its ability to recover catalytic activity completely after sulfur poisoning. Nickel segregation was characterized and quantified on powder samples by means of electron microscopy, X-ray diffraction, X-ray absorption spectroscopy, and temperature-programmed reduction–reoxidation cycles. Catalyst stability was much improved compared to impregnated Ni/La0.3Sr0.55TiO3−δ and Ni/Y0.08Zr0.92O2 anode materials. A full cell was tested under both open circuit voltage and polarized conditions, showing a ...
TL;DR: A meticulous study on NiCo-NiCoOx/Ti1-yZryO2 catalysts revealed that the synergistic effect among Lewis acid sites, basic sites and metal active sites played an important role in obtaining high yields of monomers and low rates of char formation during lignin conversion.
TL;DR: In this paper, the effect of disordered ZnAl2O4 spinel structure on glycerol carbonylation with urea was investigated with pure and physically-mixed oxide.
TL;DR: In this paper, the interactions between various phases in Ni-Cu-Al2O3 mixed oxides oxygen carriers, which were prepared from layered double hydroxides precursors, synthesized using urea and metal nitrates, were investigated.
TL;DR: In this article, the catalysts were prepared by continuous co-precipitation and characterized by specific surface area, thermogravimetric analysis, temperature-programmed desorption of CO2, and X-ray diffraction.
TL;DR: In comparison to the catalytic oxidation and non-thermal plasma (NTP) process, PPC was found to be the best process to convert TCE into CO2, in particular when Cu-Mn oxide was synthetized by redox precipitation method.
TL;DR: In this paper, a series of 0.3CeO2-ZrO 2-TiO2 mixed oxide catalysts were synthesized by hydrothermal method, which exhibited good catalytic activity in a wide temperature window (220-400°C) under a gas hourly space velocity (GHSV) of 30,000h−1 for the selective catalytic reduction of NOx with NH3.
TL;DR: In this article, the earth abundant WO3 coupled with IrO2 as mixed oxide composite was synthesized by a facile two-step chemical method and the superior performance of mixed oxide composites were perceived due to four times increase in electrochemical surface area, reduction of Tafel slope, four-fold increase of turn over frequency, electronic distortion in Ir-4f spectrum of IW-50 along with the bridging of lattice oxygen atoms between iridium and tungsten metals.
TL;DR: In this article, a series of Co/Mg-Al catalysts were used for partial oxidation of methane (POM) in a fixed-bed tubular quartz reactor under a high space velocity of 300 L N CH4/(gcat/h) and a O2/CH4 molar ratio of 0.5.
TL;DR: The results show that combining MOFs and mixed-oxide supports with bioinspired structures opens opportunities for synthesizing new materials with unique and enhanced adsorption and separation properties.
Abstract: This work reports a new approach for the synthesis of a zeolitic imidazolate framework (ZIF-8) composite. It employs the direct growth of the crystalline ZIF-8 on a mixed-metal oxide support TiO2-SiO2 (TSO), which mimics the porous structure of Populus nigra. Using the natural leaf as a template, the TSO support was prepared using a sol-gel method. The growth of the ZIF-8 layer on the TSO support was carried out by the seeds and second growth method. This method facilitates the homogeneous dispersion of ZIF-8 crystals at the surface of the TSO composite. The ZIF-8@TSO composite adsorbs methanol selectively, mainly due to the hierarchical porous structure of the mixed oxide support. As compared with the as-synthesized ZIF-8, a 50% methanol uptake is achieved in the ZIF-8@TSO composite, with only 25 wt % ZIF-8 loading. IAST simulations show that the ZIF-8@TSO composite has a preferential adsorption toward methanol when using an equimolar methanol-ethanol mixture. An opposite behavior is observed for the as-synthesized ZIF-8. The results show that combining MOFs and mixed-oxide supports with bioinspired structures opens opportunities for synthesizing new materials with unique and enhanced adsorption and separation properties.
TL;DR: In this paper, a hybrid approach of an optimized physical vapor deposition magnetron sputtering (PVDMS), electrochemical anodization as well as spin coating is proposed to improve the mechanical properties, corrosion resistance, antibacterial and osteoblast cytocompatibility performance of Ti6Al7Nb implant (Ti67IMP).
Abstract: The self-ordered architecture allows for the exact design and control of geometrical features, to achieve materials with unique properties. For this reason, mixed oxide nanotube arrays have been highly regarded by the scientific community in recent years. In the present study, a hybrid approach of an optimized physical vapor deposition magnetron sputtering (PVDMS), electrochemical anodization as well as spin coating is proposed to improve the mechanical properties, corrosion resistance, antibacterial and osteoblast cytocompatibility performance of Ti6Al7Nb implant (Ti67IMP). Accordingly, controlled decorations of mixed oxide nanotube with silver nanoparticles/graphene oxide (AgNPs/GO) were designed to assess the biofunctionality of the modified Ti6Al7Nb implant. The results show that the surface modification has dramatically reduced the viability of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) cells. Besides, the AgNPs/GO loaded mixed oxide nanotube has significantly promoted cell adhesion and spreading, compared to the bare substrate. The proposed hybrid approach can also be extended to fabricate highly complex nanoarchitectures with controlled shape and biofunctionality for various orthopedic applications.
TL;DR: In this article, the influence of electrolyte composition on coating characteristics was extensively studied using four electrolytes of increasing complexity, containing KOH, Na2SiO3 and NaAlO2.
Abstract: Coatings were prepared on TA6V alloy by plasma electrolytic oxidation (PEO) using a standard electrical signal. Influence of electrolyte composition on coating characteristics was then extensively studied using four electrolytes of increasing complexity, containing KOH, Na2SiO3 and NaAlO2. The combination of SEM, GDOES, XRD characterizations on the one hand and of thermodynamic calculations on the other hand, deeply clarified coating compositions, showing in particular that they include both amorphous and crystalline phases. Amorphous phase resulted directly from the presence of silicate in solution, and was made of complex Si-based oxides difficult to clearly identify. Depending on electrolyte composition, crystalline phases in coatings included simple oxide (i.e.anatase and rutile TiO2) and/or mixed oxide (Al2TiO5), resulting from both substrate oxidation and deposition from electrolyte. Therefore, this study successfully offered an innovative approach, combining both experimental characterizations and thermodynamic calculations, to study and tune chemical characteristics of PEO coatings on TA6V.