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Showing papers on "Mixed oxide published in 2013"


Journal ArticleDOI
TL;DR: A series of Mn-Ce mixed oxide catalysts with different molar ratio of Mn/Ce were prepared by the surfactant-template (ST) method and conventional co-precipitation (CP) method for the selective catalytic reduction of NOx with ammonia (NH3-SCR) at low temperatures as mentioned in this paper.

236 citations


Journal ArticleDOI
TL;DR: In this article, a process consisting of a set of new catalysts with optimised process conditions for the maximum production of highly pure bis(2-hydroxyethyl) terephthalate (BHET) via glycolysis was demonstrated.

171 citations


Journal ArticleDOI
TL;DR: In this paper, a novel mixed Ce-Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method, which was used as an adsorbent to remove arsenic from aqueous solutions.
Abstract: In this study, a novel mixed Ce–Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method. The CF-CNTs material was characterized by various methods, including BET surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was found that the Ce–Fe oxide was uniformly dispersed on the surface of CNTs with a mean size of 7.0 nm. The obtained CF-CNTs material was used as an adsorbent to remove arsenic from aqueous solutions. The adsorption experimental results showed that this CF-CNTs material had an excellent adsorption performance for As(V) and As(III). The adsorption processes of As(V) and As(III) could be well described by the pseudo-second-order model. The mechanistic study showed that different interactions were involved in As(V) adsorption, including electrostatic attraction and surface complexation. For As(III) adsorption, partial As(III) was oxidized to As(V) followed by the simultaneous adsorption of As(V) and As(III). It was also found that intra-particle diffusion existed in the process of adsorption on CF-CNTs, but that it was not the only rate-limiting step. The resulting CF-CNTs material can be used in a broad pH range, which suggests its great potential for the decontamination of arsenic-polluted water.

145 citations


Journal ArticleDOI
TL;DR: The main reactions involved in this NHSG process and the characteristics of the resulting mixed oxides are described in the first part of this review, underlining the decisive advantages in terms of simplicity and of control (in terms of composition, homogeneity or texture) offered by this process as mentioned in this paper.
Abstract: Despite the enormous amount of research dedicated to this topic in the last 20 years or so, there is still a need for a general, cost-effective methodology allowing the synthesis of mesoporous mixed oxide catalysts. This review deals with the synthesis and catalytic applications of mixed oxides prepared by the nonhydrolytic sol–gel (NHSG) process based on the reaction of chloride precursors with ether or alkoxide oxygen donors. This NHSG process offers simple, one-step syntheses of mixed oxides with well-controlled compositions and non-ordered mesoporous textures, avoiding the use of supercritical drying or templates. Over the last decade, this process has been used to prepare various mesoporous mixed oxide catalysts, which showed real potential in major reactions such as partial and total oxidation, reduction of NOx, alkene metathesis, or alkylation. The main reactions involved in this NHSG process and the characteristics of the resulting mixed oxides are described in the first part of this review, underlining the decisive advantages in terms of simplicity and of control (in terms of composition, homogeneity or texture) offered by this process. In a second part, the literature dealing with mixed oxide catalysts prepared by this NHSG method is exhaustively reviewed and the catalytic performance of NHSG catalysts is compared, whenever possible, to that of catalysts with similar compositions prepared by other methods. The excellent catalytic performances of NHSG-catalysts (notably Si Ti, Ti V and Si Al Mo catalysts) compared to state-of-the art aerogels or ordered mesoporous materials evidences the potential of this sol–gel method, which should open the door to the synthesis of improved catalysts and to the discovery of new catalysts.

142 citations


Journal ArticleDOI
01 Nov 2013-Fuel
TL;DR: In this article, the methanation of carbon dioxide was carried out over a high-loaded Ni-Al mixed oxide catalyst (ca. molar ratio Ni/Al = 5), prepared by conventional coprecipitation of the metal precursors.

135 citations


Journal ArticleDOI
TL;DR: In this article, WO3-TiO2 mixed oxides were synthesized by a sol-gel method employing either an inorganic salt, Na2WO4, or an organic alkoxide, W(OC2H5)6, as tungsten precursor, with different W/Ti ratios.

125 citations


Journal ArticleDOI
01 Jan 2013
TL;DR: The results indicated that the ZrO(2) nanocrystals obtained by MCM show high crystallinity and uniform size distribution than the ones prepared by CCM, and the kinetics of PCD was found to follow pseudo first-order.
Abstract: ZrO(2) nanocrystals were synthesized by the microwave combustion method (MCM) using urea as the fuel without using any template, catalyst or surfactant. For the purpose of comparison, it was also prepared using the conventional combustion method (CCM). The as-synthesized ZrO(2) was characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The results indicated that the ZrO(2) nanocrystals obtained by MCM show high crystallinity and uniform size distribution than the ones prepared by CCM. Hence, the influence of the preparation methods on the structure, morphology and optical activity of ZrO(2) was investigated systematically. Photocatalytic degradation (PCD) of 4-Chlorophenol (4-CP), a potent endocrine disrupting chemical in aqueous medium was investigated by ZrO(2) nanocrystals obtained by MCM. The kinetics of PCD was found to follow pseudo first-order. Having established that ZrO(2) was photo catalytically active, the mixed oxide catalysts of ZrO(2)-TiO(2) were also tested for the PCD of 4-CP.

118 citations


Journal ArticleDOI
01 Jun 2013-Fuel
TL;DR: In this article, mixed metal oxide carriers containing iron and copper oxides were evaluated for coal and methane CLC, and the components of CuO and Fe2O3 were optimized to obtain good reactivity while maintaining physical and chemical stability during cyclic reactions for methane-CLC and solid fuel CLC.

110 citations


Journal ArticleDOI
Xianjun Du1, Dengsong Zhang1, Ruihua Gao1, Lei Huang1, Liyi Shi1, Jianping Zhang1 
TL;DR: The modular catalysts were fabricated via the combination of the Ni-MgO-Al2O3 mixed oxide nanoplates and the mesoporous SiO2 coating and show high catalytic activity with enhanced coke- and sintering-resistance in the dry reforming of methane reaction.

109 citations


Journal ArticleDOI
TL;DR: In this article, the effects of doping Ni-based SBA-15 catalysts with Ceria-Zirconia mixed oxide (CZ) on the activity and stability of these catalysts during syngas production by methane dry reforming (MDR) were investigated.

107 citations


Journal ArticleDOI
TL;DR: In this article, a series of hydrotalcite-like layered double hydroxides (LDHx) with different Mg/Al atomic ratios were prepared by using the co-precipitation method.
Abstract: A series of hydrotalcite-like layered double hydroxides (LDHx) with different Mg/Al atomic ratios (x = 2–6) were prepared by using the co-precipitation method. Further calcination yields mixed oxides with tunable basicity. The basicity of the calcined LDHx (LDOx) strongly depends on the Mg/Al ratio and the calcination temperature. The resulting LDOx materials were used as solid base catalysts and evaluated in the transesterification between glycerol and dimethyl carbonate without use of organic solvent. The correlation between the basic properties of the solid catalysts and the catalytic performance was investigated. The activity of the LDOx catalysts was demonstrated to be proportional to the surface density of basic sites. LDO2 calcined at 600 °C exhibited maximum activity for the transesterification reaction. The beneficial effect of the optimum ratio of Mg/Al = 2 is related to its high total basicity. The LDO2 catalyst can be readily recycled while maintaining high catalytic activity and selectivity of glycerol carbonate.

Journal ArticleDOI
TL;DR: In this article, a series of Mg/Zr/Sr based mixed oxide catalysts with varying molar ratios were prepared by a co-precipitation method and X-ray diffraction and temperature programmed desorption of CO2 were used to derive the characteristics of the catalysts.

Journal ArticleDOI
TL;DR: In this paper, a series of La-Zn mixed oxide catalysts with different molar ratios were prepared and calcined at different temperatures and characterized by N2 physisorption, XRD, XPS, FT-infrared spectroscopy and temperature-programmed desorption of CO2.

Journal ArticleDOI
TL;DR: In this paper, a good correlation was found between the amount of basic sites of medium and high strength and the selectivity to butanol, and the Pd-containing mixed oxide catalysts exhibited a remarkable stability during the reaction.
Abstract: Ethanol conversion into butanol was performed over MMgAlO mixed oxide catalysts (M = Pd, Ag, Mn, Fe, Cu Sm, Yb). The highest butanol yields were obtained with the Pd-containing mixed oxide, which exhibited a remarkable stability during the reaction. A good correlation was found between the amount of basic sites of medium and high strength and the selectivity to butanol.

Journal ArticleDOI
TL;DR: In this paper, cordierite monoliths coated with Mn, Ce and Zr elements were synthesized, characterized and tested in n -butanol oxidation, and the specific reaction rates of n-butanol oxides were slightly increased when Mn species were impregnated over the Ce-Zr washcoated phase.

Journal ArticleDOI
TL;DR: In this article, the influence of iron content (Ni/Fe ranging from 3 to 1) and the calcination temperature of the catalyst precursor (773 and 1073 K) on the catalytic performance were investigated.
Abstract: Nickel–iron mixed oxides derived from reevesite, a hydrotalcite-type compound, were tested in steam reforming of ethanol for hydrogen production. The influence of iron content (Ni/Fe ranging from 3 to 1) and the calcination temperature of the catalyst precursor (773 and 1073 K) on the catalytic performance were investigated. Both parameters were essential to optimize the reforming performance. Increasing the amount of iron in the reevesite precursors affected both the chemical and activity properties of the derived mixed oxide catalysts. Iron displays a positive role in nickel-based catalysts due to the enhancement of catalytic activity and hydrogen selectivity induced by the improved dispersion of nickel and the alleviation in carbon deposition. The calcination temperature led to variations in phase composition consisting of Ni(Fe)O x solid solution and NiFe 2 O 4 , which affected the final size and dispersion of nickel species formed during the reaction. The best catalyst, with a Ni/Fe ratio of 1 and calcined at 773 K, rendered high and stable hydrogen and carbon dioxide selectivity of up to ca. 60% and 40%, respectively, low methane content, and consisted of a Ni(Fe)O x + NiFe 2 O 4 mixture with high surface area and small Ni 0 crystallites. A higher percentage of crystalline NiFe 2 O 4 attained at high calcination temperature (1073 K) associated with a lower carbon deposition resistance and probably Ni 0 sintering brings about lower activity and fast deactivation. The improved performance over catalysts calcined at lower temperature and with lower Ni/Fe ratio is motivated by the effect of iron on the structural and electronic properties of the mixed oxides, thus inducing a slow formation of metallic nickel particles and coke deposits. Features like high surface area, higher iron content, lower reducibility of nickel species and small nickel crystallite size well dispersed on the surface of the catalyst with high iron content lead to a higher activity in ethanol dehydrogenation, acetaldehyde decarbonylation and reforming, and WGS.

Journal ArticleDOI
TL;DR: In this paper, the authors explored the mixed oxide composite viz; Fe 2 O 3 -TiO 2, synthesized via thermal decomposition method, to increase the catalytic efficiency of Ni-P electrodes, the well known catalytic electrodes for hydrogen evolution reaction in alkaline medium.

Journal ArticleDOI
TL;DR: In this article, various magnesium-lanthanum mixed oxide catalysts having different mg/La molar ratio were compared and their catalytic activities for the transesterification of dimethyl carbonate (DMC) with glycerol for the synthesis of GLC were compared.

Journal ArticleDOI
TL;DR: The ceria-titania mixed metal oxide is an important component of catalysts active for the production of hydrogen through the water-gas shift reaction (CO + H2O → H2 + CO2) and the photocatalytic sp...
Abstract: The ceria–titania mixed metal oxide is an important component of catalysts active for the production of hydrogen through the water–gas shift reaction (CO + H2O → H2 + CO2) and the photocatalytic sp...

Journal ArticleDOI
TL;DR: In this article, the performances of catalysts were evaluated for the soot combustion with O 2 or O 2 /NO gases in "tight contact" condition, and the results showed that the presence of Fe in CeO 2 can increase the oxygen vacancy concentration and decrease the crystallite sizes of the catalyst.

Journal ArticleDOI
TL;DR: In this paper, an efficient material by eco-friendly green synthetic route that was characterized to be nano-structured was developed, which contained agglomerated crystalline nano-particles of dimension 10-20nm, and its empirical composition as FeCe1.1O7.6.

Journal ArticleDOI
TL;DR: The novel synthesis of Nd2Fe14B nanoparticles by a microwave assisted combustion process offers an inexpensive and facile platform to produce exchange coupled hard magnets.
Abstract: The high coercivity and excellent energy product of Nd2Fe14B hard magnets have led to a large number of high value added industrial applications. Chemical synthesis of Nd2Fe14B nanoparticles is challenging due to the large reduction potential of Nd3+ and the high tendency for Nd2Fe14B oxidation. We report the novel synthesis of Nd2Fe14B nanoparticles by a microwave assisted combustion process. The process consisted of Nd–Fe–B mixed oxide preparation by microwave assisted combustion, followed by the reduction of the mixed oxide by CaH2. This combustion process is fast, energy efficient and offers facile elemental substitution. The coercivity of the resulting powders was ∼8.0 kOe and the saturation magnetization was ∼40 emu g−1. After removal of CaO by washing, saturation magnetization increased and an energy product of 3.57 MGOe was obtained. A range of magnetic properties was obtained by varying the microwave power, reduction temperature and Nd to Fe ratio. A transition from soft to exchange coupled to hard magnetic properties was obtained by varying the composition of NdxFe1−xB8 (x varies from 7% to 40%). This synthesis procedure offers an inexpensive and facile platform to produce exchange coupled hard magnets.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the addition of alkali promoters to the Co4MnAlOx mixed oxide resulted in a modification of both electronic properties of active metals and acid-base function of the catalyst surface.
Abstract: Alkali promoted Co4MnAlOx mixed oxide (molar ratio of alkali metal/Co = 0.037) were prepared by impregnation of calcined Co–Mn–Al hydrotalcite (molar ratio Co:Mn:Al = 4:1:1) with an aqueous solution of Li, Na, K, Rb or Cs nitrate. The catalysts were characterized by AAS, SEM/EDX, N2 physisorption, XRPD, XPS, H2-TPR, TPD of CO2 and NH3 and tested for N2O decomposition in inert gas and simulated waste gas from HNO3 production. N2O conversion over alkali promoted Co4MnAlOx mixed oxide decreased in order Cs > Rb > K > Na = Co4MnAlOx > Li in inert gas and was shifted to the lower values in the presence of typical components (NOx, O2 and H2O) of flue gas. The addition of alkali promoters to the Co4MnAlOx mixed oxide resulted in a modification of both electronic properties of active metals and acid–base function of the catalyst surface. The promotional effect of alkali metals is connected with their ionization potential, the charge transfer to the catalyst and a decrease in binding energies of all catalyst components (Co, Mn, Al and O). Pilot plant verification of N2O decomposition over K-promoted Co4MnAlOx is shown.

Journal ArticleDOI
TL;DR: In this article, a series of experiments targeted at elucidating the reaction pathway suggests that copper oxide domains promote the coupling of the initial intermediate, benzylimine, with benzylamine to produce the N-benzylidenebenzylamines product (path A), with a maximum production rate of 888μmol/m 2 ǫh (13.3

Journal ArticleDOI
TL;DR: In this paper, the electrolysis of mixed FeTiO 3 /TiO 2 in a molten CaCl 2 electrolyte was conducted to prepare a high-purity, and high-opacity ferrotitanium (Fe-Ti) intermetallic alloy.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the performance of three different supported CeO 2 /ZrO 2 catalysts (3-20 ¼wt.% Ce) prepared by dry impregnation at the lab scale, and reported that they showed a lower activation energy and a similar activity dependence on the partial pressure of O 2 compared to bulk Ce 2.
Abstract: Bulk CeO 2 has been recently reported as a promising catalyst for the oxidation of HCl to Cl 2 . In order to undertake the scale up of this system, various oxides (TiO 2 , Al 2 O 3 , and low- and high-surface area ZrO 2 ) have been evaluated as carriers. Supported CeO 2 catalysts (3–20 wt.% Ce) prepared by dry impregnation were isothermally tested at the lab scale. Their performance was ranked as: CeO 2 /ZrO 2 ≫ CeO 2 /Al 2 O 3 ≥ CeO 2 /TiO 2 . Kinetic data revealed a lower activation energy and a similar activity dependence on the partial pressure of O 2 for CeO 2 /ZrO 2 compared to bulk CeO 2 . Pilot-scale testing over 3-mm pellets of this catalyst evidenced outstanding stability for 700 h on stream. In-depth characterization of the carriers and fresh catalysts by N 2 sorption, Hg porosimetry, X-ray diffraction, temperature-programmed reduction with H 2 , Raman spectroscopy, electron microscopy, and in situ prompt gamma activation analysis, enabled to rationalize the different catalytic behavior of the materials. ZrO 2 stabilizes nanostructures of CeO 2 and a Ce–Zr mixed oxide phase, which offer high dispersion and improved oxidation properties. The catalyst also shows reduced chlorine uptake, and overall stands as a better Deacon material compared to bulk CeO 2 and other supported systems. CeO 2 is present on Al 2 O 3 predominantly as well-distributed nanoparticles. Still, alumina does not induce any electronic effect, thus the supported phase behaves similarly to bulk ceria. TiO 2 , likely due to the structural collapse and dramatic sintering suffered during calcination, leads to the formation of very large ceria particles. Based on our results, CeO 2 /ZrO 2 appears as a robust and cost-effective alternative to the current RuO 2 -based catalysts for large-scale chlorine recovery.

Journal ArticleDOI
TL;DR: In this article, an atmospheric-based deposition process for Cu(In,Ga)Se2 synthesis is presented, consisting of the electrodeposition of a Cu-In-Ga mixed oxide/hydroxide layer from an aqueous solution, at room temperature, followed by a thermochemical reduction and selenization.

Journal ArticleDOI
TL;DR: The tetragonal phase of CoMn2 O4 was found to be more active and selective for vanillyl alcohol oxidation than Co3 O 4 and Mn3 O4 and high-resolution TEM characterisation revealed the morphology of MnCo-MO nanorods with a particle size of 10 nm.
Abstract: Manganese-doped cobalt mixed oxide (MnCo-MO) catalyst was prepared by a solvothermal method. The as-prepared catalyst was characterised by X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed oxidation and XRD. This catalyst gave 62 % conversion with 83 % selectivity to vanillin in 2 hours for the liquid-phase air oxidation of vanillyl alcohol without using base. Three different types of metal oxides were observed in the prepared catalyst, which could be identified as Co3 O4 , Mn3 O4 and CoMn2 O4 . Among these, the tetragonal phase of CoMn2 O4 was found to be more active and selective for vanillyl alcohol oxidation than Co3 O4 and Mn3 O4 . High-resolution TEM characterisation revealed the morphology of MnCo-MO nanorods with a particle size of 10 nm. Successful recycling of the catalyst was also established in this oxidation reaction.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of calcination temperature on the structure and catalytic activity of CuO x -CoO y -CeO 2 ternary mixed oxide (atomic Cu:Co:Ce ratio of 1:5:5) prepared by co-precipitation method.
Abstract: Influence of calcination temperature (400−800 °C) on the structure and catalytic activity of CuO x -CoO y -CeO 2 ternary mixed oxide (atomic Cu:Co:Ce ratio of 1:5:5) prepared by co-precipitation method is investigated by N 2 physisorption, XRD, TPR, TEM, TG-DTA, XPS, and CO oxidation reaction. The as-synthesized CuO x -CoO y -CeO 2 undergoes successive structural changes with the calcination temperature, involving the hydroxide dehydration below 400 °C, enhanced interaction between Co 3 O 4 and CeO 2 at ca. 600 °C, and Co 3 O 4 decomposition to CoO at 700 °C. The catalyst calcined at 600 °C shows a relative enrichment of Cu + on the surface of CuO x -CoO y -CeO 2 and an enhanced interaction between Co 3 O 4 and CeO 2 along with the appearance of oxygen vacancies in CeO 2 , which seems to be responsible for its highest catalytic activity for CO oxidation among all the tested catalysts. The complete conversion of CO is obtained at 70 °C and about 50% of CO conversion is reached at 55 °C.

Journal ArticleDOI
TL;DR: In this paper, the turnover frequency related to the total basicity and total acid sites are equal for all catalysts within a factor less than 2 and did not change with the oxygen lattice capacity (OSC), which confirms that the reaction is structure insensitive.
Abstract: The different CeO2 oxides and mixed oxide CeZrO2 showed nanosized structures and morphologies in particular distinct structural and surface properties. These catalysts were effective in the iso-synthesis reaction. The flowerlike CeO2 (F) and the mixed oxide (CeZrO2) showed the highest selectivity toward isobutene and isobutene and low methane formation. The turnover frequency (TOF) related to the total basicity and total acid sites are equal for all catalysts within a factor less than 2 and did not change with the oxygen lattice capacity (OSC), which confirms that the reaction is structure insensitive. The selectivity of total hydrocarbon and of CO2 are independent of the basic sites. However, the selectivity of total iso-C4 exhibits a linear relationship with the basic sites. The mixed oxide (CeZrO2) presented the strongest basic sites and thus the highest selectivity to iso-C4. Significant is the influence of Lewis acid sites on the selectivity of isobutene increasing and isobutane decreasing both linearly with Lewis acid sites. The ratio isobutene/isobutane presented a linear relationship with the Lewis acid sites which are directly related to OSC capacity of reducible oxides.