TiO2–SnO2 nanomaterials for gas sensing and photocatalysis

Nanopowders of TiO₂–SnO₂ over a full composition range extending from 100 mol% TiO₂ to 100 mol% SnO₂ are obtained by the sol–gel method from TTIP and SnCl₂·5H₂O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO₂ is 95 m²/g while that of SnO₂ amounts to 129 m²/g. The highest SSA of 156 m²/g is achieved at 20 mol% of TiO₂. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO₂–SnO₂ over the range of 0–80 mol% TiO₂ is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO₂) to 3.18 eV (100 mol% TiO₂).     

Oxidation of dibenzothiophene with cumene hydroperoxide on MoO3/SiO2 modified with alkaline earth metals

Catalytic oxidation of dibenzothiophene (DBT) in decalin was performed using an oil-soluble oxidant, cumene hydroperoxide (CHP), over molybdenum oxide (MoO₃) supported on silica. The effects of MoO₃ loading, reaction time and the molar ratio of CHP/DBT were investigated. At a MoO₃ loading of 15 wt%, the conversion of DBT reached 82% at 70 °C, WHSV 30 h^?1, and O/S molar ratio 3. Alkaline earth metals, such as Ca, Ba, Sr and Mg were introduced on the surface of silica, prior to the impregnation of MoO₃. The results showed that the activity in the oxidation of DBT with CHP decreased in the order: MoO₃/Ca-SiO₂ > MoO₃/Ba-SiO₂ > MoO₃/SiO₂ > MoO₃/Sr-SiO₂ > MoO₃/Mg-SiO₂. The MoO₃/Ca-SiO₂ catalysts were characterized by XRD. The DBT conversions on MoO₃/Ca-SiO₂ catalysts with various Ca/Mo ratios were studied. When the Ca/Mo ratio was 0.05, the DBT conversion was the highest (95%) at 60 °C, WHSV 30 h^?1, and O/S molar ratio 3.0.     

Catalytic decomposition of CH2Cl2 over supported Ru catalysts

Ru/TiO₂ and Ru/Al₂O₃ were prepared by wet impregnation of TiO₂ and Al₂O₃, and tested in the catalytic decomposition of dichloromethane (DCM). Ru/TiO₂ catalyst presents the higher activity than Ru/Al₂O₃ catalyst, with 50% and 90% conversion occurring at 235 and 267 °C, respectively. Moreover, the higher stability on Ru/TiO₂ catalyst is observed, which can be related to ready removal of Cl species produced during DCM decomposition. The chlorine uptake on Ru/TiO₂ catalyst is estimated at 240 °C to be 0.36 mmol Cl/g_cat, while on Ru/Al₂O₃, the value is 1.46 mmol Cl/g_cat.     

Synergy effect in the photocatalytic degradation of methylene blue on a suspended mixture of TiO2 and N-containing carbons

N-containing carbon materials were obtained from waste plum stones submitted to pyrolysis under Ar flow at 700 °C or to activation under steam at 800 °C and enriched with nitrogen by heating in a NH₃/air mixture at 270 °C or in NO at 300 °C. In situ mixtures of TiO₂ and carbons were prepared by the slurry method and methylene blue photodegradation was chosen as a model reaction to verify the influence of N-containing carbons on the photocatalytic activity of TiO₂ under artificial visible light irradiation. From the kinetics of methylene blue degradation an important synergy effect between both solids was detected with a remarkable increase up to a factor of 5.3 higher in the photocatalytic activity on TiO₂–C than that on TiO₂ alone. A mechanism for the photoassisting role of N-containing carbons upon the photoactivity of TiO₂ under visible light is discussed.     

Tungstophosphoric acid supported on titania: A solid acid catalyst in benzylation of phenol with benzylalcohol

Benzylation of phenol with benzylalcohol was carried out in liquid phase over tungstophosphoric acid (TPA) supported on titania. The catalysts were prepared with different TPA (10–25%) loading by wet impregnation method, were calcined at 700 °C and characterized by XRD, surface area, FTIR and acidity of the catalysts was measured by temperature programmed desorption of NH₃–TPD, FTIR pyridine adsorption. The catalysts have been represented by a general formula as xPTiO₂₋y (where x = wt%, P = TPA, and y = calcination temperature in °C). The 20PTiO₂ catalyst calcined at various temperatures to know the effect of calcination temperature on activity of the catalyst and the 20PTiO₂-700 showed highest activity in benzylation of phenol with benzylalcohol because it had highest acidity. The effects of temperature, catalyst weight, mole ratio of the reactants on conversion of phenol and product selectivities have been optimized. 20PTiO₂-700 catalyst gave conversion of benzylalcohol (BA) 98% and the selectivity to benzyl phenol (BP) 83.6%, phenyl benzyl ether (PBE) 9.4%, benzylether (BE) 7% at 130 °C, phenol to benzylalcohol molar ratio 2 and in 1 h.     

Selective reduction of NO by NH3 over Fe-zeolite-promoted V2O5-WO3/TiO2-based catalysts: Great suppression of N2O formation and origin of NO removal activity loss

Great depression of the formation N₂O in the selective catalytic reduction of NO by NH₃ (NH₃-SCR) has been studied by combining a V₂O₅-WO₃/TiO₂ (VWT) catalyst with a Fe-exchanged ZSM-5 zeolite (FeZ). At temperatures > 400 °C, N₂O formation was significant over VWT but < 5 ppm over FeZ/VWT catalysts with the FeZ ≥ 8%. Unfortunately, all these FeZ-promoted catalysts disclosed a decrease in deNO_xing performances, due to an enhanced NH₃ oxidation into NO. At temperatures > 350 °C, the chemically-combined VWT-based FeZ systems could facilitate both N₂O reduction with NH₃ and N₂O decomposition, thereby suppressing N₂O emissions in NH₃-SCR reaction.     

Study on SO42−/ZrO2-MoO3 in the integrative transformation of cottonseed oil deodorizing distillate

With the integrative transformation of non α-tocopherols, glycerides, free fatty acids, and methyl alcohol in cottonseed oil deodorizing distillate as the target reaction, we prepared highly catalytic SO₄^2?/ZrO₂-MoO₃ solid acid catalyst by precipitation–wet impregnation. The optimal conditions for catalyst preparation were then determined by varying sulfuric acid concentration, MoO₃ loading factor, calcination temperature, and calcination time. The structure of SO₄^2?/ZrO₂-MoO₃ solid acid catalyst was then examined by X-ray diffraction (XRD), Brunauer–Emmett–Teller measurements, scanning electron microscopy, and other methods. Results show that the MoO₃ loading factor (percentage weight ratio of MoO₃ to ZrO₂), impregnation concentration of sulfuric acid, and calcination temperature were the most important factors that influenced catalytic activity. The optimal conditions for catalyst preparation were an MoO₃ loading factor of 20%, a sulfuric acid impregnation concentration of 0.75 mol/L, a calcination temperature of 550 °C, and a calcination time of 6 h. The obtained catalyst exhibited the highest catalytic activity under these conditions.     

Tuning the microwave dielectric properties of Zn2SnO4 ceramics by adding Ca0.8Sr0.2TiO3

The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1−y)Zn₂SnO₄–yCa_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their application in microwave devices. A (1−y)Zn₂SnO₄–yCa_0.8Sr_0.2TiO₃ ceramic system was prepared by the conventional solid-state method. The X-ray diffraction patterns of the 0.85Zn₂SnO₄–0.15Ca_0.8Sr_0.2TiO₃ ceramic system did not significantly vary with sintering temperature. A dielectric constant of 9.6, a quality factor (Q×f) of 15,900 GHz, and a temperature coefficient of resonant frequency of −4 ppm/°C were obtained when the 0.85Zn₂SnO₄–0.15Ca_0.8Sr_0.2TiO₃ ceramic system was sintered at 1175 °C for 4 h.     

The molybdenum species of MoO3/SiO2 and their catalytic activities for the epoxidation of propylene with cumene hydroperoxide

The MoO₃/SiO₂ catalysts containing different surface molybdenum species were prepared by a sol–gel method, and the effects of the preparation condition and MoO₃ loading on the surface molybdenum species and property of MoO₃/SiO₂ were studied. The XRD, FT-IR, UV–vis and Raman spectroscopies were used to characterize the surface molybdenum species, and temperature-programmed desorption of NH₃ adsorbed on a catalyst was used to detect the surface acidic properties. The results show that, there were the dispersed polymolybdate, α-MoO₃, β-MoO₃, monomeric molybdenum species and silicomolybdic acid on the MoO₃/SiO₂ catalyst, and their distributions and subsistence states were affected by the preparation condition and MoO₃ loading. Different molybdenum species exhibit different catalytic activities for the epoxidation of propylene with cumene hydroperoxide. In the 15 wt% MoO₃/SiO₂ catalyst synthesized at pH 9.1 and dried appropriately, there are the small size β-MoO₃ and monomeric molybdenum species that they are mainly effective catalyst components for the epoxidation of propylene. Using this catalyst, the ～100% conversion of cumene hydroperoxide and ～100% selectivity to propylene oxide can be obtained in the tert-butyl alcohol solvent at 2.6 MPa and 80 °C for 4 h.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

Microwave dielectric properties of Pb2MoO5 ceramic with ultra-low sintering temperature

Ultra-low firing microwave dielectric ceramic Pb₂MoO₅ with monoclinic structure was prepared via a conventional solid state reaction method. The sintering temperature ranged from 530 °C to 650 °C. The relative densities of the ceramic samples were about 97% when the sintering temperature was greater than 570 °C. The best microwave dielectric properties were obtained in the ceramic sintered at 610 °C for 2 h with a permittivity ∼19.1, a Q × f value about 21,960 GHz (at 7.461 GHz) and a temperature coefficient value of −60 ppm/°C. From the X-ray diffraction, backscattered electron image results of the co-fired samples with 30 wt% silver and aluminum additive, the Pb₂MoO₅ ceramics were found not to react with Ag and Al at 610 °C for 4 h. The microwave dielectric properties and ultra-low sintering temperature of Pb₂MoO₅ ceramic make it a promising candidate for low temperature co-fired ceramic applications.     

Low temperature sintering and microwave dielectric properties of TiO2 ceramics

The TiO₂ ceramics were prepared by a solid-state reaction in the temperature range of 920–1100 °C for 2 h and 5 h using TiO₂ nano-particles (Degussa-P25 TiO₂) as the starting materials. The sinterability and microwave properties of the TiO₂ ceramics as a function of the sintering temperature were studied. It was demonstrated that the rutile phase TiO₂ ceramics with good compactness could be readily synthesized from the Degussa-P25 TiO₂ powder in the temperature range of 920–1100 °C without the addition of any glasses. Moreover, the TiO₂ ceramics sintered at 1100 °C/2 h and 920 °C/5 h demonstrated excellent microwave dielectric properties, such as permittivity (Ɛ_r) value >100, Q × f  > 23,000 GHz and τ_f ≅ 200 ppm/°C.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

SO42−–Mn–Co–Ce supported on TiO2/SiO2 with high sulfur durability for low-temperature SCR of NO with NH3

The catalysts SO₄^2 − Mn–Co–Ce/TiO₂/SiO₂ were investigated for the low-temperature SCR of NO with NH₃ in the presence of SO₂. An excellent SO₂ durability at low temperature was obtained with the catalyst used TiO₂/SiO₂ as support and modified with SO₄^2 −. The catalyst sulfated with 0.1 mol/L H₂SO₄ solution and then calcined at 300 °C exhibited the best NO_x conversion efficiency of 99.5% at 250 °C in the presence of 50 ppm SO₂. The conversion efficiency did not decrease after repeatedly used for 8 times.     

A Ce–Sn–Ox catalyst for the selective catalytic reduction of NOx with NH3

A series of Ce–Sn–O_x catalysts prepared by the facile coprecipitation method exhibited good catalytic activity in a broad temperature range from 100 °C to 400 °C for the selective catalytic reduction of NO_x with NH₃ at the space velocity of 20,000 h^− 1. The Ce₄Sn₄O_x catalyst calcined at 400 °C showed high resistance to H₂O, SO₂, K₂O and PbO under our test conditions. The better catalytic performance was associated with the synergistic effect between CeO₂ and SnO₂, which strengthened the NH₃ and NO_x adsorption capacity on the surface of the catalyst.     

Enhanced activity of MnxW0.05Ti0.95 − xO2 − δ for selective catalytic reduction of NOx with ammonia by self-propagating high-temperature synthesis

A series of TiO₂ supported MnWO_x catalysts Mn_xW_0.05Ti_0.95 − xO_2 − δ (x = 0.05, 0.1, 0.15) were synthesized by solution combustion method. The Mn_0.10W_0.05Ti_0.85O_2 − δ catalyst showed highest activity in NH₃-SCR reaction within a broad temperature range of 200 °C–400 °C. XRD and TEM results indicate that the active Mn and W species are highly dispersed over TiO₂ support in the form of nanoparticles (4–7 nm). The TEM and H₂-TPR results also suggest that a MnWO_x phase has been formed on the TiO₂, which is beneficial for the activity of the Mn_xW_0.05Ti_0.95 − xO_2 − δ catalysts in the high temperature range of 280 °C–400 °C.     

Influence of Pd-loading on gas sensing characteristics of SnO2 thick films

Nanocrystalline pristine and 0.5, 1.5 and 3.0 wt% Pd loaded SnO₂ were synthesized by a facile co-precipitation route. These powders were screen-printed on alumina substrates to form thick films to investigate their gas sensing properties. The crystal structure and morphology of different samples were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The 3.0 wt% Pd:SnO₂ showed response of 85% toward 100 ppm of LPG at operating temperature of 250 °C with fast response (8 s) and quick recovery time (24 s). The high response toward LPG on Pd loading can be attributed to lowering of crystallite size (9 nm) as well as the role of Pd particles in exhibiting spill-over mechanism on the SnO₂ surface. Also selectivity of 3.0 wt% Pd:SnO₂ toward LPG was confirmed by measuring its response to other reducing gases like acetone (CH₃COCH₃), ethanol (C₂H₅OH) and ammonia (NH₃) at optimum operating temperature.     

Trimethylamine sensing properties of nano-SnO2 prepared using microwave heating method

The precursor was obtained through the reaction between SnCl₄·5H₂O and NaOH in the presence of PEG400 (polyethylene glycol, M = 400). Tin oxide (SnO₂) nano-powders were prepared by heating the precursor with microwave method. SnO₂ thick film sensors were fabricated using SnO₂ nano-materials as sensing materials. The phase composition and morphology of the material particles were characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The average particle sizes of the samples obtained with 616 W microwave heating and 800 W microwave heating (20 min) are about 5 and 15 nm, respectively. The influence of the heating duration and heating power on the gas-sensing properties of sensors based on SnO₂ nano-materials were investigated. The sensitivities of the sensors based on SnO₂ nano-materials heated with 616 and 800 W for 20 min were higher than those of the sensors based on SnO₂ nano-materials heated with 136, 264 and 440 W for 20 min. When operating at 200–310 °C, the sensor based on SnO₂ heated with 616 W for 20 min exhibits highest sensitivities in all sensors based on SnO₂ heated with 616 W for different duration. The sensitivity to a few kinds of organic gases, such as (CH₃)₃N and (CH₃)₂CO were studied. It was found that the sensor based on SnO₂ nano-materials (with 616 W microwave heating for 20 min) exhibited good performance characterized by high sensitivity and short response time to dilute trimethylamine when operated at 255 °C. The sensitivity to 0.001 ppm (CH₃)₃N at 255 °C was 3. The response time and recovery time were about 30 and 100 s, respectively.     

Sacrificial template synthesis of core-shell SrTiO3/TiO2 heterostructured microspheres photocatalyst

The core-shell SrTiO₃/TiO₂ heterostructure was obtained via a combined hydrothermal route and calcination treatment using amorphous spherical TiO₂ as both template and reactant. Adjusting the hydrothermal environments can control the morphology of the post-calcined sample when it is hydrothermally treated at 180 °C/3 h and 200 °C/6 h, respectively. Following the heat treatment at 700 °C/4 h, the obtained powder illustrates the core-shell heterostructure with a hierarchical surface, and the diameter of the microsphere is about 700 nm. This synthesizing route facilitates the formation of a concentration gradient of SrTiO₃ and TiO₂, and subsequently constructs a gradient energy level, which helps the samples exhibited an excellent de-colorize activity over the methylene blue. The possible formation mechanism of core-shell SrTiO₃/TiO₂ heterostructures was proposed to guide the further improvement of their photocatalytic activity.     

Synthesis and characterization of NH4PO3 based composite with superior proton conductivity for intermediate temperature fuel cells

In this work, we prepared NH₄PO₃/MO₂ (MSi, Ti) composite materials with various amounts of TiO₂ using a sol–gel method, which are potential for application as electrolytes for intermediate temperature fuel cells (150–250 °C). The effect of the amount of TiO₂ on the conductivities of the composite was investigated systematically by an impedance spectroscopy within the temperature range of 50–275 °C under different atmospheres. The composite SiTiO10APP (10 mol% TiO₂) showed high proton conductivity, 0.001–0.043 S cm^?1 at 150–250 °C. The maximum conductivities are 0.043 S cm^?1 at 225 °C under humid H₂ and 0.0085 S cm^?1 at 175 °C under humid air, respectively. A thermogravimetric analysis showed the composite had high thermal stability below 300 °C. Moreover, it was found that the microstructure has significant effect on the conductivity of the composites at higher temperature.