Low temperature preparation and characterization of nanospherical anatase TiO2 and its photocatalytic activity on Congo red degradation under sunlight

Nanospherical titanium oxide with anatase structure was obtained at low temperature and normal pressure using a simple method of preparation. The dilute titanium (III) chloride solution was stirred at room temperature for several hours, and then ammonium hydroxide with hydrogen peroxide was added. A yellow gel TiO₂·xH₂O was obtained with nanodot shape and amorphous structure. Heated at 300 °C, it crystallized to pure anatase structure with nanospherical shape. The anatase particles prepared show good adsorption and photodegradation of Congo red solution under the sunlight. Materials were characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and UV spectroscopy.     

Removal of NOx from wet flue gas by corona discharge

This paper researches on the reduction of NO_x (DeNO_x) from wet flue gas by a DC corona radical shower system. The experimental results show that the water vapor in the flue gas not only reduces the corona but also reduces the discharge current. The DeNO_x efficiency and the quantity of NO_x removal per unit energy can be enhanced by raising the concentration of water vapor in the flue gas properly and the maximum quantity of NO_x removal per unit energy is more than 25.5 g as the humidity of the flue gas ranges from 10 to 12%. The longer the flue gas resides in the reactor, the higher the DeNO_x efficiency is and the lesser NO_x will be reduced by per unit power.     

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.     

Various TiO2 microcrystals: Controlled synthesis and enhanced photocatalytic activities

Titania microspheres with higher photocatalytic activity have been synthesized using TiCl₄ and FeCl₃ as the precursor in the presence of Span-80. The products were characterized with XRD, TEM and UV–vis DRS. XRD and TEM indicated that the microsphere was a mixture of rutile, brookite and anatase with a diameter of about 5–7 μm. The photocatalytic experiments revealed that the microspheres exhibited high photocatalytic activities under UV-light and solar irradiation. The degradation rate of methyl orange (MO) was 100% under UV-light irradiation for 3 h and 91% under solar irradiation for 6 h. In particular, the catalysts could be readily separated by sedimentation after the photocatalytic reaction.     

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).     

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.     

Application of the thermal DeNOx process to diesel engine DeNOx: an experimental and kinetic modelling study

Diesel DeNO_x experiments have been conducted using the selective noncatalytic ‘thermal DeNO_x’ process in a diesel fuelled combustion-driven flow reactor which simulated a single cylinder (966 cm³) and head equipped with a water-cooling jacket and an exhaust pipe. NH₃ was directly injected into the cylinder to reduce NO_x emissions. A wide range of air/fuel ratios (A/F=20-40) was selected for NO_x reduction where an initial NO_x of 530 ppm was usually maintained with a molar ratio (β=NH₃/NO_x) of 1.5.The results indicate that a 34% NO_x reduction can be achieved from the cylinder injection in the temperature range, 1100-1350 K. Most of the NO_x reduction occurs within the cylinder and head section (residence time<40 ms), since temperatures in the exhaust are too low for additional NO_x reduction. Under large gas quenching rates, increasing β values (e.g. 4.0) substantially increase the NO_x reduction up to 60%, which is comparable with those achieved under isothermal conditions. Experimental findings are analysed by chemical kinetics using the Miller and Bowman mechanism including both N/H/O species and CO/hydrocarbon reactions to account for CO/UHC oxidation effects, based on practical nonisothermal conditions. Comparisons of the kinetic calculations with the experimental data are given as regards temperature characteristics, residence time and molar ratio. In addition, the effects of CO/UHC and branching ratio (α=k₁/(k₁+k₂)) for the reaction NH₂+NO=products are discussed in terms of NO reduction features, together with practical implications.     

Transient TPSR, DRIFTS-MS and TGA studies of a Pd/ceria-zirconia catalyst in CH4 and NO2 atmospheres

In this study, the parameters governing the activity of Pd/ceria-zirconia catalysts in the selective catalytic reduction (SCR) of NO_x assisted by methane are investigated using a combination of temperature-programmed spectroscopic and thermogravimetric techniques and transient SCR conditions. By DRIFTS of adsorbed CO, it is established that Pd species on Ce_0.2Zr_0.8O₂ are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH₄ + NO₂ atmosphere, the CH₄-SCR reaction is initiated at 280 °C on Pd/Ce_0.2Zr_0.8O₂ and yields almost 100% N₂ above 500 °C. DRIFTS-MS and TGA experiments performed under transient SCR conditions show that DeNO_x activity is due to a surface reaction between some methane oxidation products on reduced Pd sites with ad-N_xO_y species presumably located on the support. The detrimental effect of O₂ on DeNO_x is explained by the promotion of the total combustion of methane assisted by the ceria-zirconia component at the expense of the SCR reaction above 320 °C.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Microwave-hydrothermal synthesis of Fe-based materials for lithium-ion batteries and supercapacitors

Fe-based materials, Fe₂O₃, Fe₃O₄, and FeOOH, were synthesized by the microwave–hydrothermal process in the temperature range of 100–200 °C and under very short reaction times of 15 min to 2 h. Under microwave-controlled hydrolysis and redox reactions, cube-like Fe₂O₃ was crystallized using FeCl₃, Fe₃O₄ particles were crystallized from FeCl₂ and FeOOH nanorods were crystallized using FeCl₃. The Fe-based materials were fabricated to make anodes and cathodes of lithium-ion battery and supercapacitor electrode materials to study their potential electrochemical applications. The electrochemical results showed that FeOOH had better anode capacity as lithium-ion batteries than those of Fe₂O₃ and Fe₃O₄. The present results suggest that the microwave–hydrothermally synthesized Fe-based materials are promising lithium-ion battery anode materials.     

Nitrogen-promoted active carbons as DeNOx catalysts: 1. The influence of modification parameters on the structure and catalytic properties

The influence of modification by post-treatment of active carbon with ammonia or urea on catalytic reduction of NO with ammonia was studied. The amount of nitrogen introduced into the structure depended on the pre-treatment of active carbon. The formed N-species were mainly pyridinic or pyrrole/pyridone in nature. No amine, amide or cyano species were found. Both modification procedures (ammonia or urea) led to the increase in activity in SCR and selectivity to N₂. The extent of the improvement depended on the pre-oxidation of active carbon before N-introduction and was higher for urea than ammonia treatment.     

Hydrothermal synthesis of LiNixCo1−xO2 cathode materials

Ultrafine powders of LiCoO₂, nonstoichiometric LiNiO₂ and LiNi_0.9Co_0.1O₂ were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/Co, Li/Ni and Li/(Ni + Co) was studied. The final products were investigated by XRD, TEM and EDS. To synthesize a stoichiometric LiNiO₂ under mild hydrothermal conditions was found to be a big challenge. Transmission electron microscopies (TEM) revealed the formation of well-crystallized LiCoO₂ and LiNi_0.9Co_0.1O₂ with average size of 100 nm and 10 nm, respectively.     

Influence of preparation conditions to structure property, NOx and SO2 sorption behavior of the BaFeO3 − x perovskite catalyst

A series of the BaFeO_3 − x perovskite catalysts was synthesized by a sol-gel method using citric acid and/or EDTA as complexants with a purpose to improve their sulfur-resistance by forming a uniform perovskite structure at a low calcination temperature, i.e. 750 °C. The thermogravimetry results show that almost no carbonate was formed after calcination of the xerogel precursor with the complexants' molar ratio of CA/EDTA ≤ 1.5, which was convinced by the in situ DRIFT spectra results of the Ba-Fe-1 catalyst during the SO₂/O₂ sorption. It indicates that, after adding EDTA into the complexants, the metal ions of the raw material could be mixed homogeneously and react stoichiometrically by calcination at 750 °C to form a uniform perovskite structure. Accordingly, the obtained Ba-Fe-1 perovskite presented a performed sulfur-resistance. Moreover, the seriously damaged structure of the BaFeO_3 − x perovskite by reduction could be in situ regenerated by calcination under lean conditions at 400 °C, which is within the operating temperature zone of the aftertreatment system of diesel to meet the real commercial demands.     

Experimental investigation on NOx emission and carbon burnout from a radially biased pulverized coal whirl burner

Experiments have been performed on 1 MW pulverized coal (pc) furnace in order to investigate the characteristics of coal combustion and NO_x emission from a new type of radially biased dual register whirl burner. The burner is characterized by a primary air pipe with a continuously changing cross-section and an impact ring. The mixture of pulverized coal and air inside the primary pipe is split into two streams, which are the outer pc rich annular jet and the inner pc lean annular jet respectively. Three Chinese coals, which are high rank bituminous coal, low rank bituminous coal and meager coal respectively, are used in the experiments. We examine the influences of various parameters such as the relative position of the over-fire air (OFA) nozzle, over-fire air ratio (19.1%), primary air ratio, inner secondary air ratio, outer secondary air ratio, inner secondary air swirling intensity, and outer secondary air swirling intensity on NO_x formation and unburned carbon in fly ash. With the primary air ratio increasing from 13.4% to 23.4%, the value of the NO_x emission of the SH coal decreases by 26.7% at first, and then increases by 21.7%. In contrast, the value of the carbon in fly ash (C_FA) increases by 40.1% at first, and then decreases by 58.3%.According to the experimental results, the influence of each individual parameter on NO_x formation and unburned carbon in fly ash agrees well with the existing literature. In this study, the influences of various combinations of these parameters are also examined, thus providing some reference for the design of the radial biased whirl burner, the configuration of the furnace and the distribution of the air.     

Effects of precursors on the surface Mn species and the activities for NO reduction over MnOx/TiO2 catalysts

TiO₂-supported manganese oxide catalysts were prepared from two different precursors, manganese nitrate (MN) and manganese acetate (MA), and these samples were characterized by BET, XRD, TG/DTA, XPS and FT–IR. The characterization results showed that the MN precursor resulted primarily in MnO₂, accompanied with some Mn-nitrate, while the MA precursor caused mainly Mn₂O₃ species. These two different precursors also led to different surface Mn atom concentrations indicated by XPS and NH₃ adsorption. Consequently, the higher low-temperature activity of MnO_x/TiO₂ from MA precursor was attributed to higher surface Mn concentration and the surface Mn₂O₃ species.     

Cationic surfactant promoted reductive electrodeposition of nanocrystalline anatase TiO2 for application to dye-sensitized solar cells

A new strategy involving the introduction of the common cationic surfactant cetyltrimethylammonium bromide (CTAB) for the cathodic deposition of titanium dioxide from hydrolyzed TiCl₄ and TiCl₃ solutions by cyclic voltammetry has been developed. Crack-free and non-transparent anatase TiO₂ films were obtained for the first time and characterized with the aid of Raman spectra and SEM. Selection of TiCl₄ as the precursor for the electrodeposition is quite a novel approach for the research in the area of dye-sensitized solar cells (DSSCs). It is noted that NO₃⁻ ion is essential for such a deposition. Under the same conditions, a thicker TiO₂ film was obtained by adding CTAB into KNO₃ electrolyte, compared with the case without it. The CTAB-promoted film led to an increased energy conversion efficiency of the corresponding DSSC. Mechanisms are proposed for the electrochemical deposition and the beneficial role of CTAB.     

Improved electrochemical performance of LiFePO4 by increasing its specific surface area

Cathode material LiFePO₄ with an excellent rate capability has been successfully prepared by a simple solid state reaction method using LiCH₃COO·2H₂O, FeC₂O₄·2H₂O and (NH₄)₂HPO₄ as the starting materials. We have investigated the effects of the sintering temperature and mixing time of the starting materials on the physical properties and electrochemical performance of LiFePO₄. It was found that the rate capability of LiFePO₄ is mainly controlled by its specific surface area and it is an effective way to improve the rate capability of the sample by increasing its specific surface area. In the present study, our prepared LiFePO₄ with a high specific surface area of 24.1 m² g⁻¹ has an excellent rate capability and can deliver 115 mAh g⁻¹ of reversible capacity even at the 5 C rate. Moreover, we have prepared lithium ion batteries based on LiFePO₄ as the cathode material and MCMB as the anode material, which showed an excellent cycling performance.     

NOx and SOx emissions of a high sulfur self-retention coal during air-staged combustion

NO_x and SO_x emissions of air-staged combustion were investigated in a 1 MW tangentially-fired furnace combusting a high sulfur self-retention coal. Two variables including the air stoichiometric ratio of primary combustion zone and the relative location of over-fire air (OFA) injection ports were studied. These results suggest that NO_x reduction efficiency monotonically increases with increasing the relative location of OFA injection ports, and the lowest NO_x emissions are achieved when the air stoichiometric ratio of primary combustion zone is 0.85. In the meantime, SO_x emissions can be effectively reduced when the air stoichiometric ratio of primary combustion zone is 0.85 or 0.95, and SO_x emissions monotonically decrease with increasing the relative location of OFA injection ports.     

Characterization of uniform,nanodispersed NOx storage catalyst materials synthesized by successive ionic layer deposition

A dispersed phase of barium oxide (BaO) supported on alumina has been shown to be primarily responsible for NO_x storage in practical lean NO_x trap catalysts. Conventional impregnation based catalyst loading techniques generate a mixture of dispersed and less active bulk-like BaO phases on alumina, with the bulk-like phase increasing as weight loading increases. Samples of equivalent BaO weight loading on fused alumina were prepared by successive ionic layer deposition (SILD) and wet impregnation. NO₂ temperature programmed desorption experiments demonstrate that SILD is uniquely capable of selectively synthesizing uniform, nanodispersed BaO rafts with high surface coverage. These nanodispersed SILD structures show remarkable thermal stability under high operating temperatures up to 650 °C.     

High surface area BaZrO3 photocatalyst prepared by base-hot-water treatment

Barium zirconate (BaZrO₃) nanoparticles have been prepared by modified sol-gel route. Low temperature process of base-hot-water treatment (BHWT) was conducted to obtain high surface area BaZrO₃. The treatments were carried out at 90 °C and at pH 14 with various concentrations of NaOH solution. Single phase nanocrystalline perovskite structure of BaZrO₃ powders was successfully obtained by immersing the BaZrO₃ precursor into hot-basic condition of 1 M NaOH solution for 1 h and consecutively calcined at 1000 °C for 2 h. BaZrO₃ powders with BHWT showed surface area of 18.4 m²/g which is nearly 8 times larger than those of the powders without BHWT. Photocatalytic activities of BaZrO₃ powders upon bleaching of methylene blue in an aqueous solution under UV light irradiation were enhanced by the increment of their surface area.