Showing papers on "Mixed oxide published in 2006"
TL;DR: In this paper, the effect of calcination temperature on the structural features and catalytic behavior of the MnO x -CeO 2 mixed oxides prepared by modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K.
Abstract: MnO x –CeO 2 mixed oxides prepared by sol–gel method, coprecipitation method and modified coprecipitation method were investigated for the complete oxidation of formaldehyde. Structure analysis by H 2 -TPR and XPS revealed that there were more Mn 4+ species and richer lattice oxygen on the surface of the catalyst prepared by the modified coprecipitation method than those of the catalysts prepared by sol–gel and coprecipitation methods, resulting in much higher catalytic activity toward complete oxidation of formaldehyde. The effect of calcination temperature on the structural features and catalytic behavior of the MnO x –CeO 2 mixed oxides prepared by the modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K. For the samples calcined below 773 K, no any diffraction peak corresponding to manganese oxides could be detected by XRD measurement due to the formation of MnO x –CeO 2 solid solution. While the diffraction peaks corresponding to MnO 2 phase in the samples calcined above 773 K were clearly observed, indicating the occurrence of phase segregation between MnO 2 and CeO 2 . Accordingly, it was supposed that the strong interaction between MnO x and CeO 2 , which depends on the preparation route and the calcination temperature, played a crucial role in determining the catalytic activity toward the complete oxidation of formaldehyde.
655 citations
TL;DR: In this paper, the short term (∼100h) oxidation behavior of 9%Cr steel P91 was studied at 650°C in N 2 -O 2 -H 2 O gas mixtures containing a relatively low oxygen level of 1%.
277 citations
TL;DR: In this paper, Mg-Al-CO3 layered double hydroxide (LDH) was synthesized, and its thermal evolution was investigated using X-ray diffraction, FTIR spectroscopy, and thermogravimetric analysis (TGA).
Abstract: Mg-Al-CO3 layered double hydroxide (LDH) was synthesized, and its thermal evolution was investigated using X-ray diffraction, FTIR spectroscopy, and thermogravimetric analysis ( TGA). The resultant LDH derivatives showed excellent CO2 adsorption capabilities, especially suitable for high- temperature CO2 separation from flue gases. Calcination of crystalline LDHs at 400 degrees C led to phase transformation yielding amorphous Mg- Al mixed oxides having a CO2 sorption capacity of 0.49 mmol/ g at 200 C. Reversible and irreversible CO2 sorption was determined to be similar to 88% and similar to 12% of the total CO2 sorption, respectively. Regeneration restored the Mg- Al mixed oxide to 98% of its initial CO2 sorption after several cycles of CO2 adsorption testing. This clearly indicates the desirable properties of Mg- Al mixed oxide for CO2 capture from flue gases at high temperatures ( up to 200 degrees C).
264 citations
TL;DR: In this paper, a co-precipitation of mixed oxides was used to varying the aging time for 4, 18 and 24 hours, and the effect of the precipitated aging time was determined by means of specific surface area measurements, X-ray diffractometry (XRD), infrared spectroscopy (FT-IR), XPS, temperature programmed reduction (TPR) and temperature programmed desorption of oxygen (O2-TPD).
Abstract: Mn-Cu mixed oxides were prepared by co-precipitation varying the aging time for 4, 18 and 24 h. The catalytic performance in propane and ethanol total oxidation on these samples was better than on Mn2O3 and CuO pure oxides. The increase of the aging time enhanced the activity and the selectivity to CO2. The nature and disposition of the phases forming the catalytic system as well as the effect of the precipitated aging time was determined by means of specific surface area measurements, X-ray diffractometry (XRD), infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and temperature programmed desorption of oxygen (O2-TPD). The catalytic behaviour seems related to the existence of a Cu1.5Mn1.5O4 mixed phase and the easier reducibility of the catalysts.
245 citations
TL;DR: Structural analyses reveal that the activity of this photocatalyst is strongly dependent on the generation of trivalent Rh-Cr mixed-oxide nanoparticles with optimal composition and distribution.
Abstract: The structure of Rh−Cr mixed-oxide (Rh2-yCryO3) nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) is characterized by electron microscopy and X-ray spectroscopy. The Rh2-yCryO3 nanoparticle is an efficient cocatalyst for photocatalytic overall water splitting on the (Ga1-xZnx)(N1-xOx) solid solution and is loaded onto the catalyst by impregnation from an aqueous solution containing Na3RhCl6·2H2O and Cr(NO3)3·9H2O followed by calcination in air. Impregnation of the (Ga1-xZnx)(N1-xOx) with 1 wt % Rh and 1.5 wt % Cr followed by calcination at 623 K for 1 h provides the highest photocatalytic activity. Structural analyses reveal that the activity of this photocatalyst is strongly dependent on the generation of trivalent Rh−Cr mixed-oxide nanoparticles with optimal composition and distribution.
175 citations
TL;DR: In this paper, a TG-FTIR and flow reactor experiments were performed to study soot oxidation on MnOx-CeO2 mixed oxide catalysts in model diesel exhaust gas (10% O2, 5% H2O, 1000 ppm NO, balance N2).
Abstract: TG-FTIR and flow reactor experiments were performed to study soot oxidation on MnOx-CeO2 mixed oxide catalysts in model diesel exhaust gas (10% O2, 5% H2O, 1000 ppm NO, balance N2). The ignition temperature in TG-FTIR experiments for a 1:20 mixture of soot and catalyst was found to be ∼280 °C, which is significantly lower than for the individual oxides. It was found that NO is oxidized over the catalyst to NO2, which is stored on the catalyst as nitrate at low temperatures. At higher temperatures the nitrates decompose, releasing NO2 to the gas phase which acts as the oxidizing agent for soot. The nitrate storage capacity of MnOx-CeO2 is three to five times higher than that of the individual oxides resulting in a major contribution of the released NO2 to the soot oxidation process. This explains the strong synergistic effect of manganese and cerium in the mixed oxide on the soot oxidation. Adding SO2 to the model gas resulted in a deactivation of the catalyst, which is traced to the loss of the NO oxidation activity. The sulphates could be decomposed by heating the catalyst under reducing as well as oxidizing conditions. However, the initial activity of the catalyst could not be restored.
167 citations
TL;DR: In this paper, a series of Pt promoted ceria-zirconia mixed oxides was prepared, characterized, and tested for the low temperature water-gas shift reaction, and an enhancement in the water gas shift rate was observed by doping zirconium atoms into ceria to form a binary oxide for Pt promoted catalysts.
Abstract: A series of Pt promoted ceria–zirconia mixed oxides was prepared, characterized, and tested for the low temperature water–gas shift reaction. An enhancement in the water–gas shift rate was observed by doping zirconium atoms into ceria to form a binary oxide for Pt promoted catalysts. By characterization using TPR and XANES, doping zirconia to ceria decreased the temperature for the surface reduction step. However, the total number of bridging OH group defect sites decreased, as Zr remained to a great extent in the Zr 4+ oxidation state. This was confirmed by CO adsorption, whereby the density of total surface formates was found to decline with increased Zr concentrations. However, the formate forward turnover rate in steam was increased by zirconia addition, and was found to be higher than either Pt/ceria or Pt/zirconia alone. Both the overall rate of the formate decomposition and the water–gas shift rate, as measured by the CO conversion, passed through a maximum with increasing Zr content. Two types of formates were observed, those associated with a ceria-rich surface phase, and those associated with a zirconia-rich surface phase. The relative amounts of the two formates correlated with the Zr/Ce atomic ratios obtained by XPS. EXAFS results provided direct evidence that a solid solution was present in the mixed oxide, as a distinct peak in the Fourier transform magnitude corresponding to the Zr–Ce interaction was observed, increasing with increasing Ce/Zr ratio. The sensitivity to added carbon dioxide in the feed of the undoped and a Zr doped catalyst was also explored.
164 citations
TL;DR: In this article, the authors investigated the effect of ceria in composite oxides for cyclohexanol de-hydrogenation and hydrogen transfer reactions, and showed that the presence of the ceria enhances the surface area and acid-base properties.
Abstract: CeO2–ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV–vis–NIR diffuse reflectance, SEM and acid–base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid–base properties facilitating the dehydrogenation process. At low ceria content, the CeO2–ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)–ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2–ZnO catalysts for reactions involving acid–base sites.
127 citations
TL;DR: In this paper, the authors investigated the performance of mixed oxide catalysts in selective catalytic reduction of NO x by NH 3 and showed a clear correlation between the dependence of these properties and the mixed oxide composition.
Abstract: Manganese–cerium mixed oxide catalysts with different molar ratio Mn/(Mn + Ce) (0, 0.25, 0.50, 0.75, 1) were prepared by citric acid method and investigated concerning their adsorption behavior, redox properties and behavior in the selective catalytic reduction of NO x by NH 3 . The studies based on pulse thermal analysis combined with mass spectroscopy and FT-IR spectroscopy uncovered a clear correlation between the dependence of these properties and the mixed oxide composition. Highest activity to nitrogen formation was found for catalysts with a molar ratio Mn/(Mn + Ce) of 0.25, whereas the activity was much lower for the pure constituent oxides. Measurements of adsorption uptake of reactants, NO x (NO, NO 2 ) and NH 3 , and reducibility showed similar dependence on the mixed oxide composition indicating a clear correlation of these properties with catalytic activity. The adsorption studies indicated that NO x and NH 3 are adsorbed on separate sites. Consecutive adsorption measurements of the reactants showed similar uptakes as separate measurements indicating that there was no interference between adsorbed reactants. Mechanistic investigations by changing the sequence of admittance of reactants (NO x , NH 3 ) indicated that at 100–150 °C nitrogen formation follows an Eley–Rideal type mechanism, where adsorbed ammonia reacts with NO x in the gas phase, whereas adsorbed NO x showed no significant reactivity under conditions used.
122 citations
TL;DR: In this article, the thermal decomposition of Co-Mn-Al layered double hydroxides (LDHs) with various Co:Mn:Al molar ratios (4:2:0, 4:1.5:0.5, and 4:0:2) was studied using high-temperature X-ray powder diffraction and thermal analysis.
120 citations
TL;DR: In this article, the authors investigated the catalytic activity of methanol-based alkylating agents for methylation of phenol and 2,6-xylenol.
TL;DR: In this paper, a mixture of 5, 10, 15, 20, 20 and 25% of alumina in silica through a hybrid sol-gel technique is synthesized.
TL;DR: In this article, the expected orthorhombic perovskite structure of the chromite is observed for all levels of substitution and maximum activity is achieved for the catalyst with x ǫ = 0.1 in which mixed oxide formation upon substitution of lanthanum by strontium in the chromites becomes maximised.
TL;DR: In this article, the vapour phase selective oxidation of 4-methylanisole to p -anisaldehyde and p-anisic acid was investigated over V 2 O 5 /Al 2 O 3 -TiO 2 catalysts containing various amounts of V 2O 5 (2 −16.5%) in the temperature range 523 −723 K under normal atmospheric pressure.
Abstract: The vapour phase selective oxidation of 4-methylanisole to p -anisaldehyde and p- anisic acid was investigated over V 2 O 5 /Al 2 O 3 -TiO 2 catalysts containing various amounts of V 2 O 5 (2–16 wt.%) in the temperature range 523–723 K under normal atmospheric pressure. The Al 2 O 3 -TiO 2 (1:1.3 mole ratio) binary oxide support was prepared by a homogenous coprecipitation method using urea as precipitating reagent. The V 2 O 5 /Al 2 O 3 -TiO 2 catalysts were prepared by a wet impregnation method from ammonium metavanadate dissolved in oxalic acid solution. The Al 2 O 3 -TiO 2 support and V 2 O 5 /Al 2 O 3 -TiO 2 catalysts were subjected to various calcination temperatures (773–1073 K) to understand the dispersion and thermal stability of catalysts and were characterized by means of X-ray diffraction, FT-infrared, X-ray photoelectron spectroscopy, O 2 chemisorption and BET surface area methods. The physicochemical characterization results reveal that the Al 2 O 3 -TiO 2 mixed oxide is homogeneous and thermally quite stable retaining titania-anatase phase up to 1073 K. The alumina-titania support also accommodates a monolayer equivalent of V 2 O 5 in a highly dispersed state when calcined at 773 K. This observation is supported from XRD, FTIR and O 2 uptake results. The XPS studies reveal that titania, alumina and vanadia are in Ti(IV), Al(III) and V(V) oxidation states irrespective of calcination temperature employed. The O 1s, Ti 2p, Al 2p and V 2p photoelectron peaks of the V 2 O 5 /Al 2 O 3 -TiO 2 samples are highly sensitive to the calcination temperature as well as V 2 O 5 coverage. The 16 wt.% V 2 O 5 /Al 2 O 3 -TiO 2 catalyst exhibits more conversion and more product selectivity to p -anisaldehyde when compared to other samples.
TL;DR: A new Pd/MgLa mixed oxide is found to be an efficient catalyst for the Sonogashira reaction of aryl iodides, bromides and even activated chlorides in the absence of a copper salt.
TL;DR: In this article, a systematic investigation was conducted on the mechanism and electrocatalytic properties of O 2 and Cl 2 evolution on mixed oxide electrodes of nominal composition: Ti/[Ru (0.3) Ti ( 0.6) Ce (0−1− x ) ]O 2 [Nb 2 O 5 ] ( x ) (0,≤ x ǫ ≥ 0.1).
TL;DR: In this article, it was shown that Cs3PO4, one of the species that may be eluted from the Cs-P-Si oxide, is an effective non-halogen homogeneous catalyst.
Abstract: Cesium–phosphorous–silicon mixed oxide (Cs–P–Si oxide), a typical acid–base bifunctional catalyst, efficiently catalyzes propylene carbonate synthesis from CO2 and propylene oxide under supercritical conditions (8–10 MPa). This catalyst contains no halogens and requires no additional solvents. A portion of the catalyst was eluted into the product solution during catalysis. It was also found that Cs3PO4, one of the species that may be eluted from the Cs–P–Si oxide, is an effective non-halogen homogeneous catalyst.
TL;DR: In this paper, the performance of Mo-V-Sb-O mixed metal oxides was investigated for the Oxidative Dehydrogenation of ethane to ethylene.
Abstract: Mo–V–Sb–O mixed metal oxides were prepared, characterized and tested for the oxidative dehydrogenation of ethane (ODH). These catalysts are active and selective in the oxidative dehydrogenation of ethane to ethylene, although their catalytic performance depends strongly on the calcination temperature. The best catalytic results were obtained on samples heat-treated at 600 °C in N 2 (with selectivities to ethylene higher than 80% at ethane conversions about 65%). Moreover, a loss in the catalyst activity is initially observed on these catalysts as a consequence of modifications in the nature of the crystalline phases. Changes on the oxidation state of antimony ions on the surface of the used catalyst have also been observed, with the appearance of Sb 5+ on the surface of used catalysts. The good catalytic performance of these catalysts is related to the presence of (SbO) 2 M 20 O 56 crystalline phase in a similar way to that proposed for selective Mo–V–Te–Nb–O mixed metal oxide catalysts.
TL;DR: In this article, the effects of incorporating Ce into ZrO2 on the catalytic activity and selectivity of Cu/Cex Zr1−x O2 for the hydrogenation of CO to methanol were investigated.
TL;DR: In this article, the authors investigated the selective oxidation of H 2 S to elemental sulfur in a fixed bed reactor using Ce-V mixed oxides and cerium oxide (CeO 2 ) catalytic materials prepared by the complexation technique.
TL;DR: In this paper, the microstructure (porosity and microchemistry) of the reduced material and microstructural examination of the mixed oxide feedstock were characterized using a field emission gun scanning electron microscope (FEG-SEM) with backscattered electron imaging (BSE) and X-ray energy dispersive spectrometry (X-EDS).
TL;DR: In this article, the memory effect of hydrotalcite was used to form Me/Mg-Al hydroalcites as the active phase on the surface of the Mg-al mixed oxide.
Abstract: Metal (Me: Fe, Co, Ni or Cu) containing Mg-Al hydrotalcite-type anionic clay catalysts have been prepared by adopting the “memory effect” of hydrotalcite and tested for Baeyer–Villiger oxidation of ketones. Mg-Al hydrotalcite was calcined to the mixed oxide and dipped in an aqueous solution of metal (Me) salt; metal species was incorporated by “memory effect” to form Me/Mg-Al hydrotalcite as the active phase on the surface of the Mg-Al mixed oxide. The activity and the structure of these catalysts have been compared with those of metal supported catalysts prepared by coprecipitation and impregnation. Among the metals tested, iron was the most effective and use of Fe(NH 4 ) 2 (SO 4 ) 2 ·6H 2 O as the metal salt resulted in the highest activity. The activity of the catalyst was higher than those prepared by coprecipitation from the nitrates of Mg, Fe and Al. Judging from Mossbauer and Fe K-edge XAFS spectra, Fe species possess the Fe 3+ valence state, are mainly octahedrally coordinated and form Fe O Fe cluster-type structure on the Mg-Al mixed oxides. This clearly indicates that the Fe 3+ O Fe 3+ cluster-type compounds are more active for the Baeyer–Villiger oxidation than well dispersed Fe 3+ species formed on the hydrotalcite prepared by coprecipitation. Six-membered cyclic ketones, such as cyclohexanone, 2-norbornone and 2-adamantanone, were effectively oxidized to the corresponding lactones by using O 2 /benzaldehyde as an oxidizing agent.
TL;DR: In this paper, the relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria−zirconia mixed oxides, CZ-MO and cZ-SO, is analyzed.
Abstract: The relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria−zirconia mixed oxides, CZ-MO and CZ-SO, is analyzed. The samples were prepared by applying to a fresh Ce0.62Zr0.38O2 mixed oxide two alternative aging routines consisting of a reduction with H2 at 1223 K (5 h), followed by either a mild, CZ-MO, or severe, CZ-SO, re-oxidation treatment. By combining high-resolution electron microscopy and a number of chemical charcterization techniques, it is shown that the nanostructure of the aged oxides, specifically the total amount and surface presence of the phase exhibiting an ordered cationic sublattice (κ-like phase), is a key factor in determining their redox response. In the low-temperature reduction range (Tredn ≤ 773 K), the enhanced reducibility of the CZ-MO sample is proposed to be kinetically controlled by its surface structure mainly consisting of the κ-like phase. In accordance with the reported results, the surface activa...
TL;DR: MnO 2 -ZrO 2 binary oxide catalytic system was applied for the effective utilization of CO 2 as an oxidant in the ethylbenzene dehydrogenation (EBD) to styrene monomer (SM).
TL;DR: In this article, the correlation between film structure and optical properties is studied by applying techniques such as Raman spectroscopy (RS), Fourier transform infrared (FTIR) and UV-vis spectrophotometry.
Abstract: Thin films of MoO 3 and mixed Mo/W oxides have been obtained by atmospheric pressure (AP)CVD, using pyrolytic decomposition of metal carbonyls. The correlation between film structure and optical properties is studied by applying techniques such as Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, and UV-vis spectrophotometry. The transmittance in the visible range of films deposited on glass substrates is about 80 %, but when deposited on conductive glass (e.g., SnO 2 :Sb/glass) the films have 60 % transmittance. After annealing, the optical transmittance of the single oxide films improves, while for the mixed oxide films it slightly decreases. The electrochromic (EC) properties of MoO 3 and mixed Mo/W oxide films have been investigated by cyclic voltammetry. Deep-blue coloring of all the EC films appears only in the cathodic range, minimizing the visible-light transmittance. In the anodic regime, the EC film starts bleaching and becomes transparent. Devices fabricated with a solid polymeric-type electrolyte and a functioning layer of mixed oxide films exhibit good reversibility of the effect, and an optical modulation of about 30 % is obtained.
01 Sep 2006
TL;DR: Three-dimensionally ordered macroporous (3 DOM) M/Ti (M=Zr or Ta) mixed oxides were prepared by cohydrolysis of a mixture of Zr(n-OC(4)H(9))(4/TTIP or TaCl(5)/TTIP (TTIP=titanium isopropoxide) combined with a polystyrene (PS) latex sphere templating technique and showed only anatase phase structure.
Abstract: Three-dimensionally ordered macroporous (3 DOM) M/Ti (M = Zr or Ta) mixed oxides were prepared by cohydrolysis of a mixture of Zr(n-OC4H9)4/TTIP or TaCl5/TTIP (TTIP = titanium isopropoxide) combined with a polystyrene (PS) latex sphere templating technique. The resulting products exhibited homogeneous wall compositions, namely, Zr or Ta was uniformly dispersed into the TiO2 framework with the loading levels of 5, 10, and 20 mol% for Zr and 2.5, 5.0, and 7.5 mol% for Ta, respectively. The estimated macropore diameter, wall thickness, and particle size of the products ranged from 280 to 290 nm, from 30 to 50 nm, and from 10 to 12 nm, respectively. The products showed only anatase phase structure although their starting solitary metal oxides exhibited suitable crystalline structures under the same preparation conditions. Raman scattering spectroscopy showed that the crystal structure of titania had a slight interference due to the incorporation of Zr or Ta, and UV–vis diffuse reflectance spectroscopy (DRS) showed the narrower band gap of the products compared with that of pure anatase TiO2. The products exhibited mesoporous wall structures, and their BET surface areas were higher than those of the corresponding pure 3 DOM metal oxides. The UV-light photocatalytic activity of the products was assessed by monitoring the photodegradation of two organic molecules including 4-nitrophenol (4-NP) and rhodamine B (RB). Both the photocatalytic reactions confirmed that the presence of the second metal oxide in the titania framework resulted in enhanced photocatalytic activity compared with the pure titania framework.
TL;DR: It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-CE bridges developed in the parent calcined samples.
Abstract: A series of Fe-Ce mixed oxides (95 atom % Fe-5 atom % Ce) has been prepared by different methods: coprecipitation, impregnation, and physical mixture of Ce and Fe oxides. These solids have been tested in the Fischer-Tropsch synthesis. The characterization of the catalytic precursors was carried out by X-ray diffraction (XRD), Raman, Mossbauer, and X-ray photoelectron (XPS) spectroscopic techniques. When the preparation method ensures a microscopic contact between Fe and Ce cations in the solid, several types of Fe-Ce interactions are present in the calcined solids. The interactions take the shape of Fe-O-Ce bridges that can exist either in the hematite-like solid solution or in the interphase between the Fe oxide covered by microcrystals of Ce oxide. In the case of the hematite-like solid solution, Ce(IV) cations are dissolved in the alpha-Fe2O3 network. The promotion by Ce of the catalytic properties observed in the final catalysts can be directly related with the detection of these Fe-O-Ce bridges in the calcined solids. The Ce promotion results in a larger yield to hydrocarbons, a higher production of olefins, and a higher selectivity to medium and large chain hydrocarbons (larger than six carbon atoms). It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-Ce bridges developed in the parent calcined samples.
TL;DR: In this article, high surface area titania supported Mn-Cu and Mn-Cr bimetallic oxides were prepared by wet impregnation method using their nitrate salts, and the catalytic activity of these materials was evaluated for selective catalytic reduction (SCR) of NO with NH 3 in the presence of excess oxygen at low temperatures.
Abstract: High surface area titania supported Mn-Cu and Mn-Cr bimetallic oxides were prepared by wet impregnation method using their nitrate salts. The catalytic activity of these materials was evaluated for selective catalytic reduction (SCR) of NO with NH 3 in the presence of excess oxygen at low temperatures (373-523 K). The surface and bulk properties of the catalysts were examined using X-ray diffraction, BET-surface area, FT-IR, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) techniques. X-ray diffraction (XRD) studies revealed the formation of definite crystalline compounds MnCrO 3 and CrMn 1.5 O 4 for Mn-Cr/TiO 2 samples and Cu 1.4 Mn 1.6 O 4 and Cu 1.5 Mn 1.5 O 4 for Mn-Cu/TiO 2 samples. The specific surface areas of the prepared catalysts were significantly lower than the pure TiO 2 support. The FT-IR studies indicate that the acidic strength of these catalysts was higher than the corresponding single oxide catalysts. TPR studies suggest that the shift in the reduction peak position toward higher temperatures in bimetallic oxides is probably due to the formation of binary or ternary metal oxide phases, as observed from XRD study. The XPS peak intensities and the corresponding binding energies indicate that the surface concentration of Mn is lower than either Cu or Cr at equal metal loadings. A slight shift of the Mn 2p XPS line toward higher binding energies (642.1 eV) was observed in the case of Mn-Cu/TiO 2 and Mn-Cr/TiO 2 catalysts. This is due to the formation of stoichiometric mixed oxide phases between promoted metal oxides, which was observed in the XRD study. The core level binding energy values indicate that the manganese is present as Mn(IV) in both the catalysts. The activity results of these catalysts were compared with their corresponding single oxide catalysts.
TL;DR: In this paper, a detailed investigation of the preparation routine for the multi-metal oxide Mo 1 V 0.30 Te 0.23 Nb 0.125 O x used as catalyst for the selective oxidation of propane to acrylic acid is presented.
Abstract: This work presents a detailed investigation of the preparation routine for the multi-metal oxide Mo 1 V 0.30 Te 0.23 Nb 0.125 O x used as catalyst for the selective oxidation of propane to acrylic acid. In situ Raman spectroscopy on the initial aqueous polyoxometalate solution prepared from ammonium heptamolybdate, ammonium metavanadate and hexaoxotelluric acid reveals the coexistence of Anderson-type anions [TeM 6 O 24 ] n − , M = Mo, V; n ≥ 6 and protonated decavanadate species [H x V 10 O 28 ] (6− x )− . Raman analysis showed that the monomeric motif of the Anderson-type tellurate is preserved after addition of the Nb precursor and the subsequent spray-drying process. Calcination of the X-ray amorphous spray-dried material in air at 548 K seems to be the essential step, leading to a re-arrangement of the tellurate building blocks, generating nanocrystalline precursors of the phases finally established during treatment in helium at 873 K.
TL;DR: In this paper, amorphous SiO 2, doped with various amount of TiO 2 2, was used as support for gold nanoparticles and the effect of the loading on the structural and surface properties was investigated by transmission electron microscopy, X-ray diffraction, Raman and Xray photoelectron spectroscopy.
Abstract: Amorphous SiO 2 , doped with various amount of TiO 2 , was used as support for gold nanoparticles. Gold was deposited through the controlled sol formation technique. The effect of the TiO 2 loading on the structural and surface properties was investigated by transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. The catalytic behavior was tested in the oxidation of CO. A significant enhancement in the activity was observed for the gold supported on mixed oxide with low TiO 2 loading. On the basis of characterization data, the positive effect is assigned to the electronic modification of the Ti(IV) of the newly formed Ti O Si bonds.