Influence of TiO2 and CeO2 on the hydrogenation activity of bulk Ni2P

TiO₂- and CeO₂-promoted bulk Ni₂P catalysts were prepared by impregnation and in-situ H₂ temperature-programmed reduction method. The prepared catalysts were characterized by XRD and XPS. The hydrogenation activities of the catalysts were studied using 1.5 wt.% 1-heptene in toluene and 1.0 wt.% phenylacetylene in ethanol as the model feeds. The results indicate that bulk Ni₂P possesses low hydrogenation activity but is tunable by simply controlling the content of the additives (TiO₂ or CeO₂), suggesting that TiO₂ and CeO₂ are effective promoters to enhance the hydrogenation activity of Ni₂P.     

Synthesis and characterization of highly stable optically passive CeO2-ZrO2 counter electrode

Transparent and adherent CeO₂-ZrO₂ thin films having film thicknesses ∼543-598 nm were spray deposited onto the conducting (fluorine doped tin oxide coated glass) substrates from a blend of equimolar concentrations of cerium nitrate hexahydrate and zirconium nitrate having different volumetric proportions (0-6 vol.% of Zr) in methanol. CeO₂-ZrO₂ films were polycrystalline with cubic fluorite crystal structure and the crystallinity was improved with increasing ZrO₂ content. Films were highly transparent (T ∼ 92%), showing decrease in band gap energy from 3.45 eV for pristine CeO₂ to 3.08-3.14 eV for CeO₂-ZrO₂ films. The different morphological features of the film obtained at various CeO₂-ZrO₂ compositions had pronounced effect on the ion storage capacity and electrochemical stability. CeO₂-ZrO₂ film prepared at 5 vol.% Zr concentration exhibited higher ion storage capacity of 24 mC cm⁻² and electrochemical stability of 10,000 cycles in 0.5 M LiClO₄ + PC electrolyte due to its film thickness (584 nm) coupled with relatively larger porosity (8%). The optically passive behavior of such CeO₂-ZrO₂ film (with 5 vol.% Zr) is affirmed by its negligible transmission modulation irrespective of repeated Li⁺ and electron insertion/extraction. The coloration efficiency of spray deposited WO₃ thin film is found to enhance from 47 to 107 cm² C⁻¹ when CeO₂-ZrO₂ is coupled as a counter electrode with WO₃ in an electrochromic device (ECD). These films can be used as stable ‘passive’ counter electrodes in electrochromic smart windows as they retain full transparency in both the oxidized and reduced states and ever-reported longevity.     

Synthesis of CeO2-ZrO2 solid solution by glycothermal method and its oxygen release capacity

The glycothermal (GT) reaction of Ce acetate and Zr alkoxide directly yielded CeO₂-ZrO₂ solid solutions in a region of low Ce content ≤40 mol%. Of the CeO₂-ZrO₂ solid solutions obtained by the GT method and subsequent calcination at 500 or 800 °C, the sample with 20 mol% Ce content had the largest BET surface area. This sample exhibited the highest Ce-based oxygen release capacity in the whole Ce/Zr composition range. The oxygen release capacities of CeO₂-ZrO₂ solid solutions synthesized by the GT method were much larger than those of the samples prepared by a coprecipitation (CP) method. The Reitveld analysis and the repetitive reduction-oxidation experiment indicated that the CeO₂-ZrO₂ solid solution synthesized by the GT method has a homogeneous structure as compared with that prepared by the CP method.     

CO hydrogenation to iso-C4 hydrocarbons over CeO2–TiO2 catalysts

CeO₂–TiO₂ (Ce:Ti = 0.25–9, molar ratio) catalysts were synthesized by a sol–gel method and the catalytic performances were evaluated in the selective synthesis of isobutene and isobutane from CO hydrogenation under the reaction conditions of 673–748 K, 1–5 MPa and 720–3000 h⁻¹. The physical properties, such as specific surface area, cumulative pore volume, average pore diameter, crystal phase and size, of the catalysts were characterized by N₂ adsorption/desorption and XRD. All the CeO₂–TiO₂ composite oxides showed higher surface areas than pure TiO₂ and CeO₂. No TiO₂ phase was detected on the samples of CeO₂–TiO₂ in which TiO₂ contents were in the range of 10–50 mol%. Crystalline Ce₂O₃ was detected in CeO₂–TiO₂ (8:2). The reaction conditions, temperature, pressure and space velocity, had obvious influences on the CO conversion and distribution of the products over CeO₂–TiO₂ (8:2) catalyst.     

The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films

Hybrid nanocomposite films of titanium dioxide (TiO₂) in polyimide (PI) from 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) and 4,4′-oxydiphthalic anhydride (ODPA) have been successfully fabricated by an in situ sol-gel process. These nanocomposite films exhibit fair good optical transparency up to 40 wt% of TiO₂ content. X-ray diffraction spectroscopy shows three sharp peaks in pure BAO-ODPA PI. It results from the intermolecular regularity. However, the intermolecular regularity in the hybrid film is disrupted by the introduction of TiO₂ nanoparticles with no sharp peak in XRD spectra. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm the formation of TiO₂ particles in PI matrix. The surface Ti content is much lower than the theoretical bulk content in all hybrid films. The ratio of the former to the latter increases with the TiO₂ content and levels off at TiO₂ wt%≥20. Transmission electron microscope (TEM) images show that the TiO₂ phase is well dispersed in the polymer matrix. The size of the TiO₂ phase increases from 10 to 40 nm when the TiO₂ content is 5-30 wt%, respectively.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Synthesis of a TiO2 ceramic membrane containing SrCo0.8Fe0.2O3 by the sol-gel method with a wet impregnation process for O2 and N2 permeation

A SrCo_0.8Fe_0.2O₃ impregnated TiO₂ membrane (TiO₂-SrCo_0.8Fe_0.2O₃ membrane) was successfully prepared using a sol-gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O₂) and nitrogen (N₂). The TiO₂ membrane was immersed in the SrCo_0.8Fe_0.2O₃ solution, dried and then calcined to affix SrCo_0.8Fe_0.2O₃ into the membrane. The effect of the acid/alkoxide (H⁺/Ti⁴⁺) molar ratio of the TiO₂ sol on the TiO₂ phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO₂ and SrCo_0.8Fe_0.2O₃ was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO₂-SrCo_0.8Fe_0.2O₃ membrane with fully crystallized anatase and SrCo_0.8Fe_0.2O₃ phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO₂ membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO₂ and TiO₂-SrCo_0.8Fe_0.2O₃ membranes exhibited high permeances. The TiO₂-SrCo_0.8Fe_0.2O₃ membrane developed provided greater O₂/N₂ selectivity compared to the TiO₂ membrane alone.     

Effect of CeO2 addition on densification and microstructure of Al2O3-YSZ composites

Alumina (Al₂O₃) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO₂) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al₂O₃ based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl₁₁O₁₈ grains was observed in the ceria containing composites sintered at 1400 °C. Al₂O₃-YSZ composites without CeO₂ had higher hardness than monolithic Al₂O₃ sintered body and the hardness of Al₂O₃-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO₂ increased from 10 to 30 vol%. The fracture toughness of Al₂O₃ increased from 2.8 MPa m^1/2 to 5.6 MPa m^1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m^1/2, was achieved with the addition of 30 vol% YSZ.     

Onset coarsening-coalescence kinetics of ZrO2 and less refractory TiO2 nanoparticles: Effect of homologous temperature and phase transformation

Specific surface area change of ZrO₂ (predominant tetragonal - (t) symmetry, 30-50 nm) and less refractory TiO₂ anatase nanoparticles (20-50 nm) upon isothermal firing at 700-1000 °C in air was determined by N₂ adsorption-desorption hysteresis isotherm. The nanoparticles underwent onset coarsening-coalescence within minutes without appreciable phase transformation for TiO₂, but with extensive transformation into monoclinic (m-) symmetry for ZrO₂. The apparent activation energy of such a process being not much higher for ZrO₂ (77 ± 23 kJ/mol) than TiO₂ (56 ± 3 kJ/mol) nanoparticles can be attributed to transformation plasticity. The minimum temperature for coarsening/coalescence of the present ZrO₂ and TiO₂ nanoparticles was estimated as 710 and 641 °C, respectively.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

Chemical reduction of nanocrystalline CeO2

The reduction of commercial and mechanochemically processed CeO₂ powders was studied. Nanostructured CeO₂, with the crystallite size of 21 nm and the lattice distortion of 0.37%, was obtained during 60 min of milling in a high-energetic vibratory mill. X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller method were applied to characterize the milled powders. During the thermal treatment at 1200 and 1400 °C in an argon atmosphere the nonstoichiometric CeO_2−x oxides with the defect fluorite structure were formed. Compositions of CeO_2−x oxides were determined according to its lattice parameter. The results showed that the release of oxygen, as well as the rate of reduction, was more effective in nanocrystalline then in the microcrystalline CeO₂, producing at 1200 °C CeO_1.80 and CeO_1.85 oxides, while at 1400 °C were obtained similarly, CeO_1.77 and CeO_1.78, compositions.     

Meldola blue immobilized on a new SiO2/TiO2/graphite composite for electrocatalytic oxidation of NADH

Meldola blue immobilized on a new SiO₂/TiO₂/graphite composite was applied in the electrocatalytic oxidation of NADH. The materials were prepared by the sol-gel processing method and characterized by several techniques including scanning electronic microscopy coupled to energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electronic microscopy (HRTEM). Si and Ti mapping profiles on the surface showed a homogeneous distribution of the components. Ti2p binding energy peaks indicate that the formation of Si-O-Ti linkage is presumably the responsible for the high rigidity of the matrices. The good electrical conductivity presented by the composites (5 and 11 S cm⁻¹) can be related to a homogeneous distribution of graphite particles observed by TEM. After the materials characterization, a SiO₂/TiO₂/graphite electrode was prepared and some chemical modifications were performed on its surface to promote the adsorption of meldola blue. The resulting system presented electrocatalytic properties toward the oxidation of NADH, decreasing the oxidation potential to −120 mV. The proposed sensor showed a wide linear response range from 0.018 to 7.29 mmol l⁻¹ and limit of detection of 0.008 mmol l⁻¹. SiO₂/TiO₂/graphite has shown to be a promising material to be used as a suitable support in the construction of new electrochemical sensors.     

Effect of Ta2O5 in (Ca,Si, Ta)-doped TiO2 ceramic varistors

TiO₂ varistors doped with 0.2 mol% Ca, 0.4 mol% Si and different concentrations of Ta were obtained by ceramic sintering processing at 1350 °C. The effect of Ta on the microstructures, nonlinear electrical behavior and dielectric properties of the (Ca, Si, Ta)-doped TiO₂ ceramics were investigated. The ceramics have nonlinear coefficients of α = 3.0–5.0 and ultrahigh relative dielectric constants which is up to 10⁴. Experimental evidence shows that small quantities of Ta₂O₅ improve the nonlinear properties of the samples significantly. It was found that an optimal doping composition of 0.8 mol% Ta₂O₅ leads to a low breakdown voltage of 14.7 V/mm, a high nonlinear constant of 4.8 and an ultrahigh electrical permittivity of 5.0 × 10⁴ and tg δ = 0.66 (measured at 1 kHz), which is consistent with the highest and narrowest grain boundary barriers of the ceramics. In view of these electrical characteristics, the TiO₂–0.8 mol% Ta₂O₅ ceramic is a viable candidate for capacitor–varistor functional devices. The characteristics of the ceramics can be explained by the effect and the maximum of the substitution of Ta⁵⁺ for Ti⁴⁺.     

Synthesis and electrochemical characterization of nano-CeO2-coated nanostructure LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ spinel cathode materials were coated with 0.5, 1.0, and 1.5 wt.% CeO₂ by a polymeric process, followed by calcination at 850 °C for 6 h in air. The surface-coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). XRD patterns of CeO₂-coated LiMn₂O₄ revealed that the coating did not affect the crystal structure or the Fd3m space group of the cathode materials compared to uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated using SEM, TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 20 nm. The XPS data illustrated that the CeO₂ completely coated the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the uncoated and CeO₂-coated LiMn₂O₄ cathode materials were measured in the potential range of 3.0-4.5 V (0.5 C rate) at 30 °C and 60 °C. Among them, the 1.0 wt.% of CeO₂-coated spinel LiMn₂O₄ cathode satisfies the structural stability, high reversible capacity and excellent electrochemical performances of rechargeable lithium batteries.     

Effect of ceria on the structure and catalytic activity of V2O5/TiO2–ZrO2 for oxidehydrogenation of ethylbenzene to styrene utilizing CO2 as soft oxidant

The present study was undertaken to investigate the influence of ceria on the physicochemical and catalytic properties of V₂O₅/TiO₂–ZrO₂ for oxidative dehydrogenation of ethylbenzene to styrene utilizing CO₂ as a soft oxidant. Monolayer equivalents of ceria, vanadia and ceria–vanadia combination over TiO₂–ZrO₂ (TZ) support were impregnated by a coprecipitation and wet impregnation methods. Synthesized catalysts were characterized by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction, transmission electron microscopy and BET surface area methods. The XRD profiles of 550 °C calcined samples revealed amorphous nature of the materials. Upon increasing calcination temperature to 750 °C, in addition to ZrTiO₄ peaks, few other lines due to ZrV₂O₇ and CeVO₄ were observed. The XPS V 2p results revealed the existence of V⁴⁺ and V⁵⁺ species at 550 and 750 °C calcinations temperatures, respectively. TEM analysis suggested the presence of nanosized (<7 nm) particles with narrow range distribution. Raman measurements confirmed the formation ZrTiO₄ under high temperature treatments. TPR measurements suggested a facile reduction of CeO₂–V₂O₅/TZ sample. Among various samples evaluated, the CeO₂–V₂O₅/TZ sample exhibited highest conversion and nearly 100% product selectivity. In particular, the addition of ceria to V₂O₅/TZ suppressed the coke deposition and allowed a stable and high catalytic activity.     

Morphology control of cathodically deposited TiO2 films

This work demonstrates that the microstructure of TiO₂ film can be designed and controlled by adjusting the temperature and cycle number of cathodic deposition in a solution containing TiCl₃ and NaNO₃. The redox interactions between TiCl₃ and NO₃⁻ are investigated by in situ ultraviolet-visible (UV-vis) absorption spectroscopy. Linear sweep voltammetry (LSV) is employed to study the NO₃⁻ reduction and to clarify the deposition behavior of TiO₂ in the designed plating solution. The decrease in TiO₂ deposition rate with the TiO₂ thickness may be due to the poor electron conductivity of TiO₂ depressing the generation rate of OH⁻ from the NO₃⁻ reduction. The morphology and size of TiO₂ aggregates are strongly influenced by varying the deposition temperature from 5 to 50 °C and a maximal rate of TiO₂ deposition is obtained at 25-35 °C. TiO₂ deposited at 25 °C is the roughest with a roughness factor (Ra) of ca. 67 nm. This study provides a useful method to control the morphology and deposition rate of TiO₂ film for practical photoelectrochemical applications.     

Preparation of MnOx/TiO2 ultrafine nanocomposite with large surface area and its enhanced toluene oxidation at low temperature

The TiO₂ support materials were synthesized by a chemical vapor condensation (CVC) method and the subsequent MnO_x/TiO₂ catalysts were prepared by an impregnation method. Catalytic oxidation of toluene on the MnO_x/TiO₂ catalysts was examined with ozone. These catalysts had a smaller particle size (9.1 nm) and a higher surface area (299.5 m² g⁻¹) compared to MnO_x/P25-TiO₂ catalysts. The catalysts show high catalytic activity with the ozone oxidation of toluene even at low temperature. As a result, the synthesized support material by the CVC method gave more active catalyst.     

Synthesis and reaction mechanism of Ti3SiC2 ternary compound by carbothermal reduction of TiO2 and SiO2 powder mixtures

The present study aims to investigate synthesis of Ti₃SiC₂ from TiO₂ and SiO₂ powder mixtures by carbothermal reduction method. Equilibrium TiO₂–SiO₂–C ternary phase diagram was used to predict the conditions for the formation of Ti₃SiC₂ at 1800 K under Ar atmosphere. A reactant mixture with a TiO₂:SiO₂ molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti₃SiC₂ at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti₃SiC₂ phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti₃SiC₂ contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO₂:SiO₂ molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti₃SiC₂ content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti₃SiC₂ nanolaminates. Equilibrium thermodynamic analysis of the TiO₂–SiO₂–C system suggested that the reaction of solid Ti₂O₃ with SiO and CO gases may play a dominant role in the formation of Ti₃SiC₂.     

Effect of heat treatment on 7Na2O-23B2O3-70SiO2 glass

Porous 7Na₂O-23B₂O₃-70SiO₂ glass was successfully fabricated by acid leaching treatment and phase-separation. The 2 mol/l hydrochloric acid (HCl) solution treatment was used for 24 h. Thermal analysis and X-ray diffraction were used to identify the temperature range of heat-treatment. The average pore size and the pore volume were investigated by a nitrogen adsorption instrument, and SEM was used to characterize the appearance of the porous glass. The results show that the average size of pores changed from 3.75 nm to 3.03 nm when heat treated at 640-680 °C for 6 h. In addition, when heat treated at 640 °C for 6-24 h, the pore size fell from 3.75 nm to 3.66 nm. The surface area and pore volume become larger with the increase in both temperature and heat treatment time.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.