Ce Species Research Articles

Soot combustion over Ce1-xFexO2-δ and CeO2/Fe2O3 catalysts: Roles of solid solution and interfacial interactions in the mixed oxides

Two series of CeO2–Fe2O3 catalysts (CeO2–based and Fe2O3–supported oxides) with varying composition were synthesized by a hydrothermal method and characterized using various techniques. The comparison on the activity and thermal stability of different catalysts for low-temperature soot oxidation was also performed. The presence of both Ce–Fe–O solid solution and CeO2–Fe2O3 interaction were observed over the two types of catalysts. The oxygen vacancy in the solid solution is the crucial active site to facilitating the soot combustion over the CeO2–based samples. Small CeO2 nanoparticles are well dispersed on the Fe2O3–supported catalysts, which results in the formation of Fe–O–Ce species due to the strong CeO2–Fe2O3 interaction. The Fe–O–Ce species could achieve the coupling of the Ce4+–Ce3+ and Fe3+–Fe2+ couples in the CeO2–Fe2O3 interface, which is also identified as an active species for catalytic soot oxidation. The concentration of oxygen vacancy is closely related to the content of iron in ceria lattice, while the formation of Fe–O–Ce species strongly relies on the particle size of CeO2. It is also found that the oxygen vacancy is more active than the Fe–O–Ce species for soot oxidation, but it is very easy to decompose at high temperature, resulting in obvious deactivation of catalysts. By contrast, the Fe–O–Ce species is very stable under high-temperature treatments. For the fresh samples, the CeO2–based and Fe2O3–supported catalysts showed comparable catalytic activity. After long term aging at 800°C, the loss on activity over the CeO2–based catalyst (Ce–Fe–O solid solution) is much higher than that over the Fe2O3–supported sample. The Fe2O3–supported catalysts are more suitable for practical application than the Ce–Fe–O solid solution.

CeOx doping on a TiO2-SiO2 supporter enhances Ag based adsorptive desulfurization for diesel

In this work, the impact of CeOx doping on a TiO2-SiO2 supporter on the Ag based adsorptive desulfurization for China's standard diesel was studied. The dispersion and valence states of Ce, Ti and Ag species were characterized, and the impact of Ce doping was investigated. The results indicated that Ce species and Ti species were dispersed evenly on the surface of SiO2 via a novel co-impregnation method. Following CeOx doping, the Ag species were in the form of oxides (about 5 nm) instead of metallic Ag particles (about 35 nm), which is due to the large amount of coordinative unsaturated sites provided by the interaction between CeOx and TiO2, as well as the oxidation-reduction property of CeOx. The Ag in the active oxide state (Ag2O2) and dispersed evenly on the supporter could interact with sulfur compounds more favorably, and therefore showed a good performance in the adsorptive desulfurization. In both static batch and dynamic breakthrough desulfurization tests, Ag-CeOx/TiO2-SiO2 was proved to be a more efficient adsorbent compared with Ag-TiO2-SiO2. It was found that the desulfurization performance of Ag-TiO2-SiO2 exhibited an excellent improvement (22.5%) after being doped with CeOx. In the static equilibrium tests, the equilibrium sulfur capacity of Ag-CeOx/TiO2-SiO2 was up to 5.38 mg/g for CN-II diesel (sulfur content 952.9 mg/kg) and the sulfur content of the CN-IV diesel (sulfur content 39.0 mg/kg) after desulfurization was less than 10 mg/kg, which could meet the CN-V standard.

Promotional Effect of Ce on Iron-Based Catalysts for Selective Catalytic Reduction of NO with NH3

A series of Fe–Ce–Ti catalysts were prepared via co-precipitation method to investigate the effect of doping Ce into Fe–Ti catalysts for selective catalytic reduction of NO with NH3. The NO conversion over Fe–Ce–Ti catalysts was considerably improved after Ce doping compared to that of Fe–Ti catalysts. The Fe(0.2)–Ce(0.4)–Ti catalysts exhibited superior catalytic activity to that of Fe(0.2)–Ti catalysts. The obtained catalysts were characterized by N2 adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), temperature programmed desorption (NH3-TPD), Fourier transform infrared (FT-IR) spectrophotometry, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The data showed that the introduction of Ce results in higher surface area and better dispersion of active components on the catalyst surface and enhances the amount of surface acid sites. The interactions between Fe and Ce species were found to improve the redox ability of the catalyst, which promotes catalytic performance at low temperature. The XPS results revealed that Fe3+/Fe2+ and Ce4+/Ce3+ coexisted on the catalyst surface and that Ti was in 4+ oxidation state on catalyst surface. Ce doping increased the atomic ratio of Fe/Ti and Ce/Ti and enhanced the surface adsorbed oxygen species. In addition, Fe(0.2)–Ce(0.4)–Ti catalyst also showed better tolerance to H2O and SO2 and up to 92% NO conversion at 270 °C with 200 ppm SO2 added over 25 h, which suggests that it is a promising industrial catalyst for mid-low temperature NH3–selective catalytic reduction (SCR) reaction.

Surface CuO, Bi2O3, and CeO2 Species Supported in TiO2-Anatase: Study of Interface Effects in Toluene Photodegradation Quantum Efficiency.

The enhancement of active triggered by surface deposition of Cu, Bi, and Ce containing oxidic species onto a high surface area anatase is analyzed through the calculation of the quantum efficiency for toluene photodegradation under UV and Sunlight-type illumination. To this end, series of Cu, Bi, and Ce containing oxides supported on anatase were synthesized having a growing content of the Cu, Bi, and Ce surface species and characterized with X-ray diffraction and photoelectron, UV-visible, and photoluminescence spectroscopies as well as transmission electron microscopy. Utilizing the surface concentration of Cu, Bi, and Ce species as a tool, we analyzed the influence of the system physicochemical properties affecting quantum efficiency in anatase-based materials. First, employing small surface concentrations of the Cu, Bi, and Ce species deposited onto (the unperturbed) anatase, we provided evidence that all steps of the photocatalytic event, including light absorption, charge recombination, as well as surface interaction with the pollutant and chemical output as to activity and selectivity have significance in the quantitative assessment of the enhancement of the efficiency parameter. Second, we analyzed samples rendering maximum quantum efficiency within all these series of materials. The study indicates that maximum enhancement over anatase displays a magnitude strongly dependent on the efficiency level of calculation and would thus require the use of the most accurate one, and that it occurs through a balance between optoelectronic and chemical properties of the composite materials. The (Cu, Bi, Ce) oxide-anatase interface plays a major role modulating the optoelectronic properties of the solids and thus the efficiency observable.

Role of surface Ni and Ce species of Ni/CeO2 catalyst in CO2 methanation

CeO2, which was used as support to prepare mesoporous Ni/CeO2 catalyst, was prepared by the hard-template method. The prepared NiO/CeO2 precursor and Ni/CeO2 catalyst were studied by H2–TPR, in-situ XPS, and in-situ FT-IR. The catalytic properties of the prepared Ni/CeO2 catalyst were also investigated by CO2 catalytic hydrogenation methanation. H2–TPR and in-situ XPS results showed that metal Ni species and surface oxygen vacancies could be formed by H2 reduction. In-situ FT-IR and in-situ XPS results indicated that CO2 molecules could be reduced by active metal Ni species and surface oxygen vacancies to generate active CO species and promote CO2 methanation. The Ni/CeO2 catalyst presented the high CO2 methanation activity, and CO2 conversion and CH4 selectivity reached 91.1% and 100% at 340°C and atmospheric pressure.

Protonation/Reduction of Carbonyl-Rich Diiron Complexes and the Direct Observation of Triprotonated Species: Insights into the Electrocatalytic Mechanism of Hydrogen Formation

Both the reduced and the protonated states of diiron dithiolate complexes, which are key intermediate species for the electrocatalytic production of hydrogen, have been spectroscopically and theoretically investigated in this study. Five important states in the process of H2 evolution have been characterized. In the presence of a superacid, protonation occurs onto the Fe–Fe vector of [(μ-xdt)Fe2(CO)6] (xdt: pdt, 1,3-propanedithiolate; edt, 1,2-ethanedithiolate; bdt, 1,2-benzenedithiolate) to yield the cationic μ-H species (the C state). A single reduction at 193 K leads to the neutral species (the CE state), with similar structures for the pdt and edt bridgeheads. The CE species of the bdt analogue is unstable under the same conditions. An open structure resulting from the rupture of one Fe–S bond is suggested by DFT calculations. Subsequently, a second reduction induces a dramatic structural rearrangement in which the CEE state possesses an open structure exhibiting a μ-H and a μ-CO group. Protonation on...

Effect of synthesis methods on activity of V2O5/CeO2/WO3-TiO2 catalyst for selective catalytic reduction of NOx with NH3

AbstractThe effect of synthesis methods on the activity of V/Ce/WTi catalysts was investigated for the selective catalytic reduction (SCR) of NOx by NH3. V/Ce/WTi-DP (deposition precipitation) catalyst showed excellent NH3-SCR performance, especially the better medium-temperature activity and the less N2O formation than V/Ce/WTi-IMP (impregnation). These catalysts were characterized by X-ray diffraction (XRD), Brumauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), and in situ DRIFTS techniques. The XPS and H2-TPR results revealed that V/Ce/WTi-DP exhibited more surface Ce species, higher level of Oα and higher reducibility of Ce species. Reflected by in situ DRIFTS results, the deposition precipitation method (DP) contributed to a greater amount of weakly adsorbed NO2, monodentate nitrate and NH3 species with better reactive activity. Meanwhile, the cis-N2O22– species, an intermediate for N2O formation, was very limited. As a result, these advantages brought about the superior SCR activity and N2 selectivity for V/Ce/WTi-DP.

CO oxidation and COPrOx over preformed Au nanoparticles supported over nanoshaped CeO2

Au/CeO2 (0.25% wt. Au) catalysts were prepared by anchoring preformed Au nanoparticles over ceria polycrystals, cubes and rods and tested in the oxidation of CO and COPrOx. The use of preformed Au nanoparticles assured a constant Au particle size (ca. 5nm by HRTEM) for all samples, which allowed to a precise assessment of the effect of the morphology of nanoshaped ceria on catalytic activity. The catalytic performance of the Au/CeO2-rods was much better than that of the Au/CeO2-polycrystals and Au/CeO2-cubes both in the oxidation of CO and COPrOx reactions. The Au/CeO2-rods exhibited the highest amount of oxidized Au and Ce(III) species by XPS, whereas in the Au/CeO2-cubes gold was totally metallic and the amount of Ce(III) was minimum. An intermediate situation was encountered in the Au/CeO2-polycrystals. Considering the differences in the oxidation states of Au and Ce and the fact that all samples were prepared with preformed metallic Au nanoparticles of the same size, the results indicate that the intrinsic nature of the different ceria surfaces exerts a prominent role in the gold-ceria interaction and in the electron density transfer from Au to Ce, which in turn has a strong effect on catalytic activity. Gold nanoparticles strongly interact with CeO2-{110} surfaces with respect to CeO2-{111} and CeO2-{100}, even when Au nanoparticles are prepared separately and simply deposited by impregnation.

Cerium oxide and hydrogen co-doped indium oxide films for high-efficiency silicon heterojunction solar cells

CeO2 and hydrogen co-doped In2O3 (ICO:H) films deposited by ion plating with dc arc-discharge were used as a transparent conducting oxide (TCO) electrode in hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction (SHJ) solar cells. Incorporating ICO:H instead of conventional Sn-doped In2O3 (ITO) films and hydrogenated In2O3 (IO:H) films, improved the fill factor (FF) and short-circuit current density (Jsc) simultaneously. The best SHJ cell (243.4cm2) containing ICO:H films had a conversion efficiency of 24.1%, open-circuit voltage of 745mV, Jsc of 38.8mA/cm2, and FF of 83.2% because of their high Hall mobility of 140cm2/Vs. We have clarified the following design principles for ICO:H films: (i) the Ce species substituted for In atoms acts as a donor and (ii) CeO2 and H decrease the residual strain and the contribution of the grain boundary scattering to carrier transport. This co-doping method can produce high conversion efficiencies in all solar cells containing TCO with resistive emitters.

Ce-promoted Ni/SBA-15 catalysts for anisole hydrotreating under mild conditions

Ce-containing SBA-15 materials with Ce/Si molar ratio ranging from 0 to 0.08 were prepared by mixing an acidic suspension of colloidal CeO2 particles along with the surfactant during the synthesis of mesostructured silica. The obtained solids were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms, TEM, UV–vis, and Raman spectroscopy. Structural analyses confirmed that all the samples present a well-ordered hexagonal mesoporous structure, with larger pore diameter and volume than unmodified SBA-15 due to the incorporation of the lanthanide promoter. According to the characterization results different cerium species, namely dispersed Ce species and CeO2 crystallites, are formed depending on the Ce/Si ratio of the Ce-SBA-15 materials. On the other hand, Ni/Ce-SBA-15 catalysts were prepared by wet impregnation of the mesoporous supports and the comparison of the different samples showed that the incorporation of Ce progressively enhances Ni dispersion. These catalysts were assayed for hydrotreating of anisole at temperatures in the 270–290°C range and moderate hydrogen pressure (7bar). Such process is relevant for the upgrading of bio-oils derived from the pyrolysis of lignocellulosic biomass. Catalytic activity tests reveal that conversion of anisole progressively improves with increasing Ce/Si ratio and exceeds 30% at 290°C for the catalyst with Ce/Si=0.08. In these conditions the main product is methoxycyclohexane in all cases. However, almost a two-fold increment of benzene yields can be obtained with Ce-promoted catalysts when compared to Ni/SBA-15. This enhancement of the selectivity towards aromatic is very promising for the development of a green route for the production of those chemicals.

Oxidation of Formamidines by Cerium(IV) in Aqueous Perchlorate Solutions: A Kinetics and Mechanistic Approach

The kinetics of oxidation of one of the formamidine derivatives, namely, methylaminopyrazole formamidine (MAPF) by cerium(IV) has been investigated in aqueous perchlorate solutions at a constant ionic strength of 1.2 mol dm-3 and at 25°C. The progress of the reaction was followed spectrophotometrically. The reaction exhibited a first order kinetics with respect to [Ce(IV)], whereas the order with respect to [MAPF] was found to be less than unity. The reaction rate decreased with the increase in acid concentration with a negative less than unit order. The rate of reaction was not affected by increasing either ionic strength or dielectric constant of the medium. Furthermore, addition of cerium(III) product did not affect the reaction rate. The plausible oxidation mechanism involves formation of an intermediate complex between MAPF substrate and the kinetically active species of cerium(IV) in a pre-equilibrium step which decomposes in the slow step to give free radical derived from the substrate and Ce(III). The free radical is attacked by another Ce(IV) species to yield the final oxidation products which were identified by spectral and chemical analyses as methylaminopyrazole, dimethylamine and carbon dioxide. The activation parameters have been evaluated and discussed. The rate law associated with the reaction mechanism was derived.

The Superior Performance of Sol–Gel Made Ce–O–P Catalyst for Selective Catalytic Reduction of NO with NH3

In this paper, a sol–gel made Ce–O–P catalyst (referred to as Ce–O–P-SG) was employed for selective catalytic reduction (SCR) of NOx with NH3, which was directly compared with two other Ce–O–P samples as synthesized via hydrothermal and coprecipitation routes (referred to as Ce–O–P-HT and Ce–O–P-CP, respectively). Experimental results revealed that the Ce–O–P-SG catalyst yielded a more than 90% NO conversion at 200 °C in the presence of 10 vol % H2O, whereas Ce–O–P-HT and Ce–O–P-CP catalysts only showed 50% and 20% NO conversions under the same conditions, respectively. After subjected to a series of characterization technologies (e.g., XRD, BET-BJH, XPS, NH3-TPD, py-IR, and H2-TPR), it was found that more enriched surface Ce(4+) species were formed except for the two main CePO4 phases (monazite and rhabdophane phases) of the Ce–O–P-SG catalyst compared to the other two samples, resulting in the increase of surficial active oxygen ions content. This could lead to an enhancement in surface acidity and redo...

Cerium doped red mud catalytic ozonation for bezafibrate degradation in wastewater: Efficiency, intermediates, and toxicity.

In this study, the performance of bezafibrate (BZF) degradation and detoxification in the aqueous phase using cerium-modified red mud (RM) catalysts prepared using different cerium sources and synthesis methods were evaluated. Experimental results showed that the surface cerium modification was responsible for the development of the catalytic activity of RM and this was influenced by the cerium source and the synthesis method. Catalyst prepared from cerium (IV) by precipitation was found to show the best catalytic activity in BZF degradation and detoxification. Reactive oxygen species including peroxides, hydroxyl radicals, and super oxide ions were identified in all reactions and we proposed the corresponding catalytic reaction mechanism for each catalyst that prepared from different cerium source and method. This was supported by the intermediates profiles that were generated upon BZF degradation. The surface and the structural properties of cerium-modified RM were characterized in detail by several analytical methods. Two interesting findings were made: (1) the surface texture (specific surface area and mesoporous volume) influenced the catalytic reaction pathway; and (2) Ce(III) species and oxygen vacancies were generated on the surface of the catalyst after cerium modification. This plays an important role in the development of the catalytic activity.

Plasma-catalytic degradation of benzene over Ag–Ce bimetallic oxide catalysts using hybrid surface/packed-bed discharge plasmas

Plasma-assisted catalysis has been employed for the degradation of benzene by hybrid surface/packed-bed discharge (HSPBD) plasmas over a series of Agx Ce1−x/γ-Al2O3 catalysts in in-plasma catalysis (IPC) and post-plasma catalysis (PPC) configurations. In order to study the influence of catalysts placement on discharge characteristics and the consequent synergetic effect in plasma-catalysis process, the catalysts were introduced inside and downstream the surface discharge region (region I) and packed-bed discharge region (region II), respectively, and the benzene degradation performance was investigated in these systems. The effects of the Ag/Ce molar ratio and water vapor have also been investigated in terms of benzene degradation efficiency and CO2 selectivity. Compared with the plasma-only process, the combination of plasma with Agx Ce1−x/γ-Al2O3 catalyst significantly improved the reaction performance, and the combined degradation efficiency is a synergistic effect rather than simply an additive effect. Besides, the emission of discharge products (O3 and NOx) and hazardous intermediates (formic acid and CO) was markedly suppressed with the introduction of catalyst. The highest benzene degradation efficiency of 96.2% and CO2 selectivity of 77.3% can be achieved with Ag0.9Ce0.1/γ-Al2O3 catalyst at the SIE of 400J/L. This result suggests that the interaction between a certain proportion of Ag and Ce species over the catalyst is capable of activating the surface lattice and generating more surface adsorbed oxygen (Oads), which favors the plasma-catalytic oxidation reaction. PPC processes can decompose O3 and destroy benzene more effectively than IPC processes, especially when the catalyst was introduced downstream the region II. Adding a small amount of water vapor into plasma-catalysis system enhanced the catalyst activity, however, further increased the water vapor caused an obvious negative impact on the catalyst activity.

Effect of strongly bound copper species in copper–ceria catalyst for preferential oxidation of carbon monoxide

Copper–ceria catalysts with the Cu contents up to 40at.% were prepared by the coprecipitation method. Ammonium carbonate was used as the leaching agent on the as-calcined samples to remove the weakly bound copper species. The parent and leached catalysts were tested for the preferential oxidation of carbon monoxide (CO-PROX) reaction from 40 to 200°C in 1%CO/1%O2/50%H2/N2 with a space velocity of 60,000mLh−1gcat−1. When the Cu doping amount reached 30at.%, the stable and constant CO-PROX reactivity, including CO conversion and O2 selectivity, was presented for both parent and ammonium carbonate leached catalysts. The fresh and used samples have been carefully characterized by various techniques such as power X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H2-TPR). It was confirmed that there are two different types of copper species, i.e. weakly bound CuOx clusters and strongly bound Cu–[Ox]–Ce structure, in both parent and leached catalysts. Furthermore, we have demonstrated that the weakly bound CuOx clusters removed by ammonium carbonate can be recovered by the migration of Cu–[Ox]–Ce species under the reduction or reaction conditions. The strongly bound copper species in CeO2 have been identified to be the reservoir for the active Cu sites for CO-PROX.

Ce–Fe-modified zeolite-rich tuff to remove Ba2+-like 226Ra2+ in presence of As(V) and F− from aqueous media as pollutants of drinking water

The sorption behavior of the Ba2+-like 226Ra2+ in the presence of H2AsO4−/HAsO42− and F− from aqueous media using Ce–Fe-modified zeolite-rich tuff was investigated in this work. The Na-modified zeolite-rich tuff was also considered for comparison purposes. The zeolite-rich tuff collected from Wyoming (US) was in contact with NaCl and CeCl3–FeCl3 solutions to obtain the Na- and Ce–Fe-modified zeolite-rich tuffs (ZUSNa and ZUSCeFe). These zeolites were characterized by scanning electron microscopy and X-ray diffraction. The BET-specific surface and the points of zero charge were determined as well as the content of Na, Ce and Fe by neutron activation analysis. The textural characteristics and the point of zero charge were changed by the presence of Ce and Fe species in the zeolitic network. A linear model described the Ba2+-like 226Ra2+ sorption isotherms and the distribution coefficients (Kd) varied with respect to the metallic species present in the zeolitic material. The As(V) oxianionic chemical species and F− affected this parameter when the Ba2+-like 226Ra2+-As(V)-F− solutions were in contact with ZUSCeFe. The H2AsO4−/HAsO42− and F− were adsorbed by ZUSCeFe in the same amount, independent of the concentration of Ba2+-like 226Ra2+ in the initial solution.

Highly active and stable Ni/SBA-15 catalysts prepared by a “two solvents” method for dry reforming of methane

Two series of Ni (2.5–7.5 wt%) and Ce (6 wt%) containing SBA-15 catalysts were prepared and tested in dry reforming of methane, a promising route for the production of syngas. Both Ni and Ce species were introduced in the organized mesoporous silica support in the form of nitrate salts using the “two solvents” procedure that is known to favor metal dispersion inside the porosity. Samples characterizations by N2 sorption, SAXS, XRD, SEM and TEM indicate good preservation of the porosities after Ni deposition and calcination as well as formation of NiO nanoparticles entrapped in the porous channels. In the cerium-enriched samples, the CeO2 nanoparticles are also highly dispersed. After reduction, all the catalysts show high activity and selectivity towards H2 and CO at atmospheric pressure with full CH4 conversion below 650 °C. In these conditions, there is no significant promotional effect by ceria. Moreover, prolonged tests performed at 500 °C for 12 h reveal a high stability of the catalysts. The absence of deactivation throughout the catalytic run at this temperature agrees with the low carbon amount detected after test and with the limited sintering of the Ni nanoparticles in the used catalysts. The positive effect of the SBA-15 mesoporous channels towards stabilization of the supported particles is discussed.

Ni–Ce–Al composite oxide catalysts synthesized by solution combustion method: Enhanced catalytic activity for CO methanation

Ce-incorporated Ni/γ-Al2O3 catalysts, with Ce loadings from 0wt% to 8wt%, were prepared by solution combustion method (SCM) and evaluated for CO methanation. Compared with Ce-free Ni/γ-Al2O3 catalyst, Ce-doped Ni/γ-Al2O3 catalysts retained higher low- and high-temperature catalytic activity. The Ce-doped Ni/γ-Al2O3 catalyst with Ce content of 6wt% (Ni–6Ce) maintained 100% CO conversion and nearly 100% CH4 selectivity throughout the low-temperature activity test. It is revealed that the promotional effects of Ce species were possibly attributed to the high dispersion and the resultant small sized Ni particles, owing to the formation of Ni–Ce–Al composite oxides. Furthermore, Ce4+/Ce3+ redox couples in Ce-doped catalysts enriched electrons on Ni atoms, facilitating CO dissociation, and thus the conversion. Moreover, Ni–Ce–Al composite oxide catalysts retained better coke-resistant performance at water free condition, leading to higher catalytic activity at high-temperature reaction.

Study of the growth of CeO2 nanoparticles onto titanate nanotubes

We report the study of the growth of CeO2 nanoparticles on the external walls and Ce4+ intercalation within the titanate nanotubes. The materials were fully characterized by multiple techniques, such as: Raman spectroscopy, infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The ion exchange processes in the titanate nanotubes were carried out using different concentrations of Ce4+ in aqueous solution. Our results indicate that the growth of CeO2 nanoparticles grown mediated by the hydrolysis in the colloidal species of Ce and the attachment onto the titanate nanotubes happened and get it strongly anchored to the titanate nanotube surface by a simple electrostatic interaction between the nanoparticles and titanate nanotubes, which can explain the small size and even distribution of nanoparticles on titanate supports. It was demonstrated that it is possible to control the amount and size of CeO2 nanoparticles onto the nanotube surface, the species of the Ce ions intercalated between the layers of titanate nanotubes, and the materials could be tuned for using in specific catalysis in according with the amount of CeO2 nanoparticles, their oxygen vacancies/defects and the types of Ce species (Ce4+ or Ce3+) present into the nanotubes.

Low temperature catalytic combustion of 1,2-dichlorobenzene over CeO2–TiO2 mixed oxide catalysts

Ce1−xTixO2 mixed oxide catalysts with various Ti/Ce+Ti ratios were prepared by sol–gel way and used in catalytic combustion of 1,2-dichlorobenzene (o-DCB). Characterization by XRD, Raman, HRTEM, XPS, H2-TPR, O2-TPD, CO2-TPD and NH3-TPD revealed that Ce1−xTixO2 catalysts were identified as the forms of fluorite, monocline and anatase. The incorporation of Ti distorted the crystal structure and thus increased greatly the acidity and the oxygen mobility at high temperature. Ce1−xTixO2 catalysts had considerable activity for o-DCB combustion. TOF obtained on the catalyst with Ti/Ce+Ti ratio of 0.1 at 275°C reached the highest value of 0.64μmol/minm2 (Ti). Ti improved the stability of Ce1−xTixO2 catalysts through retarding the exchange of Cl for basic lattice oxygen and hydroxyl groups. High stability maintained at 330°C for at least 50h. In situ FTIR indicated that o-DCB adsorption was much stronger on Ti species than Ce species and different reaction pathways were related to different types of oxygen species existing on the surface of Ce1−xTixO2 catalysts.