Synthesis and characterization of CuO/TiO2 catalysts for low-temperature CO oxidation

In this paper, the CuO/TiO₂ catalysts prepared by the deposition–precipitation (DP) method were extensively investigated for CO oxidation reaction. The structural characters of the CuO/TiO₂ catalysts were comparatively investigated by TG-DTA, XRD, and XPS measurements. It was shown that the catalytic behavior of CuO/TiO₂ catalysts greatly depended on the TiO₂-support calcination temperature, the CuO loading amount and the CuO/TiO₂ catalysts calcination temperature. CuO supported on the anatase phase of TiO₂-support calcined at 400 °C showed better catalytic activity than those supported on TiO₂ calcined at 500 and 700 °C. Among all our investigated catalysts with CuO loading from 2% to 12%, the catalyst with 8 wt% CuO loading exhibited the highest catalytic activity. The optimum calcination temperature of the CuO/TiO₂ catalysts was 300 °C. The XRD results indicated that the catalytic activity of the CuO/TiO₂ catalysts was related to the crystal phase and particle size of TiO₂ support and CuO active component.     

Facile preparation of Na-free anatase TiO2 film with highly photocatalytic activity on soda-lime glass

Na-free anatase TiO₂ film was prepared on soda-lime glass (SL-glass) from a TiF₄ aqueous solution upon addition of boric acid at 60 °C. It was found that the as-prepared TiO₂ film before calcination showed a higher photocatalytic activity than the calcined sample (500 °C). This could be attributed to the fact that the calcined TiO₂ film contained decent Na⁺ ions, which was diffused from the SL-glass substrate into the TiO₂ film during calcination, resulting in the decrease of photocatalytic activity.     

Synthesis of nano-crystalline Ce0.9Gd0.1O1.95 electrolyte by novel sol–gel thermolysis process for IT-SOFCs

In the present work, nano-crystalline Ce_0.9Gd_0.1O_1.95 (GDC) powder has been successfully prepared by a novel sol–gel thermolysis method using a unique combination of urea and PVA. The gel precursor obtained during the process was calcined at 400 and 600 °C for 2 h. A range of analyzing techniques including XRD, TGA, BET, SEM, EDS and TEM were employed to characterize the physical and chemical properties of obtained powders. GDC gel precursors calcined at 400 and 600 °C were found to have an average crystallite size of 10 and 19 nm, respectively. From the result of XRD patterns, we found that well-crystalline cubic fluorite structure GDC was obtained by calcining the precursor gel at 400 and 600 °C. It has been also found that the sintered samples with lower temperature calcined powder showed better sinterability as well as higher ionic conductivity of 2.21 × 10⁻² S cm⁻¹ at 700 °C in air.     

The effects of regeneration-phase CO and/or H2 amount on the performance of a NOX storage/reduction catalyst

The effects of regeneration-phase CO and/or H₂, and their amounts as a function of temperature on the trapping and reduction of NO_X over a model and a commercial NO_X storage/reduction catalyst have been evaluated. Overall, for both catalysts, their NO_X removal performance improved with each incremental increase in H₂ concentration. For the commercial sample, using CO at 200 °C, beyond a small amount added, was found to decrease performance. The addition of H₂ to the CO-containing mixtures resulted in improved performance at 200 °C, but the presence of the CO still resulted in decreased performance in comparison to activity when just H₂ was used. With the model sample, the presence of CO resulted in very poor performance at 200 °C, even with H₂. The data suggest that CO poisons Pt sites, including Pt-catalyzed nitrate decomposition. At 300 °C, H₂, CO, and mixtures of the two were comparable for trapping and reduction of NO_X, although with the model sample H₂ did prove consistently better. With the commercial sample, H₂ and CO were again comparable at 500 °C, but mixtures of the two led to slightly improved performance, while yet again H₂ and H₂-containing mixtures proved better than CO when testing the model sample. NH₃ formation was observed under most test conditions used. At 200 °C, NH₃ formation increased with each increase in H₂, while at 500 °C, the amount of NH₃ formed when using the mixtures was higher than that when using either H₂ or CO. This coincides with the improved performance observed with the mixtures when testing the commercial.     

Influence of sulfur on the structural, surface properties and photocatalytic activity of sulfated TiO2

TiO₂ materials were prepared by sol–gel method and then impregnated with sulfuric acid and calcined using different temperatures and atmosphere (air and nitrogen). Systematic variation of these two experimental parameters makes possible to modulate the amount of surface sulfur from the impregnation procedure. The best photocatalyst for liquid phenol degradation was obtained after calcination at 700 °C in air, while gas toluene degradation optimum performance is obtained by calcination at 700 °C in nitrogen from 500 °C. Structural analysis of these materials by XRD, micro-Raman spectroscopy and FE-SEM shows that once calcined at 700 °C the material was a well-crystallized, high surface area anatase structure in all cases. The surface characterization by FTIR and XPS confirms the presence of a higher amount of sulfur species and acidic OH groups in samples partially calcined in nitrogen, and a low XPS O/Ti-atomic ratio with the O 1s peak shifted to higher binding energies (1.8 vs. 2 ± 0.1 and 530.4 eV vs. 529.8 eV, respectively, against the reference materials) for samples calcined at 700 °C, temperature at which most of sulfate species have been evolved. The paper presents an attempt to correlate the contribution of the observed structural defects within the anatase sub-surface layers and surface acidity to the different photoactivity behaviour exhibited for phenol liquid phase and toluene gas phase photodegradation.     

NOx storage behavior and sulfur-resisting performance of the third-generation NSR catalysts Pt/K/TiO2–ZrO2

The NO_x storage and reduction (NSR) catalysts Pt/K/TiO₂–ZrO₂ were prepared by an impregnation method. The techniques of XRD, NH₃-TPD, CO₂-TPD, H₂-TPR and in situDRIFTS were employed to investigate their NO_x storage behavior and sulfur-resisting performance. It is revealed that the storage capacity and sulfur-resisting ability of these catalysts depend strongly on the calcination temperature of the support. The catalyst with theist support calcined at 500 °C, exhibits the largest specific surface area but the lowest storage capacity. With increasing calcination temperature, the NO_x storage capacity of the catalyst improves greatly, but the sulfur-resisting ability of the catalyst decreases. In situ DRIFTS results show that free nitrate species and bulk sulfates are the main storage and sulfation species, respectively, for all the catalysts studied. The CO₂-TPD results indicate that the decomposition performance of K₂CO₃ is largely determined by the surface property of the TiO₂–ZrO₂ support. The interaction between the surface hydroxyl of the support and K₂CO₃ promotes the decomposition of K₂CO₃ to form –OK groups bound to the support, leading to low NO_x storage capacity but high sulfur-resisting ability, while the interaction between the highly dispersed K₂CO₃ species and Lewis acid sites gives rise to high NO_x storage capacity but decreased sulfur-resisting ability. The optimal calcination temperature of TiO₂–ZrO₂ support is 650 °C.     

Solid acidities of SiO2–TiO2/montmorillonite composites synthesized under different pH conditions

SiO₂–TiO₂/montmorillonite composites were prepared under acidic, neutral and basic conditions and the solid acidity of the resulting composites were determined. All the SiO₂/TiO₂ ratio of the colloidal particles was set at 10 but the resulting SiO₂/TiO₂ ratios were significantly richer in TiO₂. The XRD patterns of the acidic composite showed expanding and broadening of the (001) reflection by intercalation of colloidal SiO₂–TiO₂ particles, but the neutral and basic composites showed only broadening of the reflections and no intercalation. The specific surface areas of the acidic, neutral and basic composites (375, 237 and 247 m²/g, respectively) were much larger than of montmorillonite (6 m²/g). The average pore sizes were about 4, 15 and 50 nm, and the amounts of solid acidic sites measured by the NH₃-TPD were 178, 95 and 86 µmol/g for the acidic, neutral and basic composites, respectively. The solid acid amount of the acidic composite was twice that of a commercial catalyst, K-10, (85 µmol/g) and much higher than the guest phase SiO₂–TiO₂ gel (16 µmol/g) or the host phase montmorillonite (6 µmol/g). The TPD peak temperatures reflect the acid strength, and were similar in all the samples, ranging from 175° to 200 °C.     

Nano-gold supported on Fe2O3: A highly active catalyst for low temperature oxidative destruction of methane green house gas from exhaust/waste gases

A number of nano-gold catalysts were prepared by depositing gold on different metal oxides (viz. Fe₂O₃, Al₂O₃, Co₃O₄, MnO₂, CeO₂, MgO, Ga₂O₃ and TiO₂), using the homogeneous deposition precipitation (HDP) technique. The catalysts were evaluated for their performance in the combustion of methane (1 mol% in air) at different temperatures (300–600 °C) for a GHSV of 51,000 h⁻¹. The supported nano-gold catalysts have been characterized for their gold loading (by ICP) and gold particle size (by TEM/HRTEM or XRD peak broadening). Among these nano-gold catalysts, the Au/Fe₂O₃ (Au loading = 6.1% and Au particle size = 8.5 nm) showed excellent performance. For this catalyst, temperature required for half the methane combustion was 387 °C, which is lower than that required for Pd(1%)/Al₂O₃ (400 °C) and Pt(1%)/Al₂O₃ (500 °C) under identical conditions. A detailed investigation on the influence of space velocity (GHSV = 10,000–100,000 cm³ g⁻¹ h⁻¹) at different temperatures (200–600 °C) on the oxidative destruction of methane over the Au/Fe₂O₃ catalyst has also been carried out. The Au/Fe₂O₃ catalyst prepared by the HDP method showed much higher methane combustion activity than that prepared by the conventional deposition precipitation (DP) method. The XPS analysis showed the presence of Au in the different oxidation states (Au⁰, Au¹⁺ and Au³⁺) in the catalyst.     

Low temperature deposition of titanium oxide containing thin films in trench features from titanium diisopropoxide bis(dipivaloylmethanate) in supercritical CO2

We studied supercritical carbon dioxide fluid deposition of titanium oxide (TiO₂) in trench features on Si substrates using a flow-type deposition apparatus from titanium diisopropoxide bis(dipivaloylmethanate), aiming at fabricating conformal films at a relatively low temperature. We investigated the deposition rate and step coverage under a fluid temperature from 40 to 60 °C, a pressure from 8.0 to 10.0 MPa, and a substrate temperature from 80 to 120 °C. They were dependent on the fluid density, indicating that the solubility difference between the bulk fluid and the neighborhood of the substrate surface plays a decisive role for the deposition. An excellent conformal filling of the trench features was achieved from the fluid of 60 °C under 8 MPa on the substrate kept at 80–100 °C. The XPS spectra of the deposited film suggested partial formation of TiO₂, and the XRD spectra showed the existence of some crystalline TiO₂ (anatase).     

Characterization of Ce0.9Gd0.1O1.95 powders synthesized by spray drying

Ce_0.9Gd_0.1O_1.95 powders were synthesized by spray drying and successive calcinations. The phase purity, BET surface area, and particle morphology of as-sprayed and calcined powders were characterized. After calcination above 300 °C, the powders were single phase and showed a BET surface area of 68 m²/g when calcined at 300 °C. The conductivity, in air, of sintered pellets was measured by electrochemical impedance spectroscopy (EIS) and it was found to be comparable with literature values. The activation energy for the total conductivity was around 0.83 eV. The powder calcined at lower temperature showed better sinterability and higher total conductivity due to an increased bulk conductivity.     

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.     

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.     

Gas phase hydrogenation of maleic anhydride to tetrahydrofuran by Cu/ZnO/TiO2 catalysts in the presence of n-butanol

Cu/ZnO/TiO₂ catalysts were prepared via the coprecipitation method. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectrometry, temperature programmed reduction, and N₂ adsorption. The catalytic activity of Cu/ZnO/TiO₂ catalyst in gas phase hydrogenation of maleic anhydride in the presence of n-butanol was studied at 235–280 °C and 1 MPa. The conversion of maleic anhydride was more than 95.7% and the selectivity of tetrahydrofuran was up to 92.7%. At the same time, n-butanol was converted to butyraldehyde and butyl butyrate via reactions, namely, dehydrogenation, disproportionation, and esterification. There were two kinds of CuO species present in the calcined Cu/ZnO/TiO₂ catalysts. At a lower copper content, the CuO species strongly interacted with ZnO and TiO₂; at a higher copper content, both the surface-anchored and bulk CuO species were present. The metallic copper (CuO) produced by the reduction of the surface-anchored CuO species favored the deep hydrogenation of maleic anhydride to tetrahydrofuran. The deep hydrogenation activity of Cu/ZnO/TiO₂ catalyst increased with the decrease of crystallite sizes of CuO and the increase of microstrain values. Compensations of reaction heat and H₂ in the coupling reaction of maleic anhydride hydrogenation and n-butanol dehydrogenation were distinct.     

Preparation of nanosized anatase TiO2-coated kaolin composites and their pigmentary properties

Nanosized anatase TiO₂-coated kaolin composites were prepared by the chemical deposition method starting from calcined kaolin and TiCl₄. The resultant TiO₂ nanoparticles on the kaolin surfaces existed in anatase phase after calcination at 200, 400, and 900 °C for 1 h, respectively. The surfaces of the kaolin powders were uniformly coated by a monolayer of TiO₂ nanoparticles. The higher calcination temperature was beneficial to formation of well crystallized anatase TiO₂ nanoparticles. The light scattering indexes of the TiO₂-coated calcined kaolin composites were two times higher than that of the kaolin substrate. XPS analysis shows that TiO₂ coating layers anchored at the kaolin surfaces via the Ti-O-Si and Ti-O-Al bonds.     

Chlorobenzene total oxidation over palladium supported on ZrO2, TiO2 nanostructured supports

Two series of supported Pd catalysts were synthesized on new mesoporous–macroporous supports (ZrO₂, TiO₂) labelled M (Zr and Ti). The deposition of palladium was carried out by wet impregnation on the calcined TiO₂ and ZrO₂ supports at 400 °C (Pd/Zr₄, Pd/Ti₄) and 600 °C (Pd/Zr₆, Pd/Ti₆) and followed by a calcination at 400 °C for 4 h. The pre-reduced Pd/MX catalysts were investigated for the chlorobenzene total oxidation and their catalytic properties where compared to those of a reference catalyst Pd/Ti-Ref (TiO₂ from Huntsman Tioxide recalcined at 500 °C) and of a palladium supported on the fresh mesoporous–macroporous TiO₂ (Pd/Ti). Based on the activity determined by T₅₀, the Pd/Ti and Pd/Ti₄ catalysts have been found to be more active than the reference one. Moreover activity decreased owing to the sequence: Pd/TiX  Pd/ZrX and in each series when the temperature of calcination of the support was raised. The overall results clearly showed that the activity was dependant on the nature of the support. The better activity of Pd/TiX compared to Pd/ZrX was likely due to a better reducibility of the TiO₂ support (Ti⁴⁺ into Ti³⁺) leading to an enhancement of the oxygen mobility. Production of polychlorinated benzenes PhCl_x (x = 2–6) and of Cl₂ was also observed. Nevertheless at 500 °C the selectivity in HCl was higher than 90% for the best catalysts.     

Low-temperature firing and microwave dielectric properties of 16CaO–9Li2O–12Sm2O3–63TiO2 ceramics with V2O5 addition

The sintering behaviors and microwave dielectric properties of the 16CaO–9Li₂O–12Sm₂O₃–63TiO₂ (abbreviated CLST) ceramics with different amounts of V₂O₅ addition had been investigated in this paper. The sintering temperature of the CLST ceramic had been efficiently decreased by nearly 100 °C. No secondary phase was observed in the CLST ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLST ceramics with small amounts of V₂O₅ addition could be well sintered at 1200 °C for 3 h without much degradation in the microwave dielectric properties. Especially, the 0.75 wt.% V₂O₅-doped ceramics sintered at 1200 °C for 3 h have optimum microwave dielectric properties of Kr = 100.4, Q × f = 5600 GHz, and TCF = 7 ppm/°C. Obviously, V₂O₅ could be a suitable sintering aid that improves densification and microwave dielectric properties of the CLST ceramics.     

Ceria modified MnOx/TiO2 as a superior catalyst for NO reduction with NH3 at low-temperature

A series of cerium modified MnOx/TiO₂ catalysts were prepared by sol–gel method and used for low-temperature selective catalytic reduction (SCR) of NOx with ammonia. The experimental results showed that NO conversion could be improved by doping Ce from 39% to 84% at 80 °C with a gas hourly space velocity (GHSV) of 40,000 h⁻¹. This activity improvement may be contributed to the increase of chemisorbed oxygen and acidity after Ce doping. TPR results also verified that the redox property of Ce modified MnOx/TiO₂ was enhanced at low-temperature.     

Catalytic reduction of NH4NO3 by NO: Effects of solid acids and implications for low temperature DeNOx processes

Ammonium nitrate is thermally stable below 250 °C and could potentially deactivate low temperature NO_x reduction catalysts by blocking active sites. It is shown that NO reduces neat NH₄NO₃ above its 170 °C melting point, while acidic solids catalyze this reaction even at temperatures below 100 °C. NO₂, a product of the reduction, can dimerize and then dissociate in molten NH₄NO₃ to NO⁺ + NO₃⁻, and may be stabilized within the melt as either an adduct or as HNO₂ formed from the hydrolysis of NO⁺ or N₂O₄. The other product of reduction, NH₄NO₂, readily decomposes at ≤100 °C to N₂ and H₂O, the desired end products of DeNO_x catalysis. A mechanism for the acid catalyzed reduction of NH₄NO₃ by NO is proposed, with HNO₃ as an intermediate. These findings indicate that the use of acidic catalysts or promoters in DeNO_x systems could help mitigate catalyst deactivation at low operating temperatures (<150 °C).     

iso-Octane partial oxidation over Ni-Sn/Ce0.75Zr0.25O2 catalysts

In this study, Ni/Ce_0.75Zr_0.25O₂ catalyst was doped with different amounts of Sn by co-impregnation method. The catalysts were characterized by BET, H₂ chemisorption, XRD, TPR, TEM, XPS and tested for iso-octane partial oxidation (iC8POX) to H₂ in the temperature range of 400–800 °C at atmospheric pressure. The results showed that most of Sn species were present on the surface of Ni particles and did not modify the reducibility of the support. Addition of a small amount of Sn (<0.5 wt.%) lowered the catalytic activity for iso-octane partial oxidation by less than 5% while the extent of carbon deposition was decreased by more than 50%. However, Sn loadings higher than 1 wt.% caused a massive drop in catalytic activity. This indicates that as long as the Ni surface is only partially covered with Sn species, the active sites for the partial oxidation of iso-octane remain intact, while the surface site ensembles required for carbon formation are blocked.