Optimization of experimental conditions based on Taguchi robust design for the preparation of nano-sized TiO2 particles by solution combustion method

This investigation was aimed at preparing nanocrystalline TiO₂ powder by solution combustion method, and searching the optimum preparing conditions by employing Taguchi robust design method. Taguchi robust design method with L₁₈ orthogonal array was implemented to optimize experimental conditions for preparing nano-sized titania particles. Titanium IV n-butoxide was hydrolyzed to obtain titany1 hydroxide [TiO(OH)₂], and titanyl nitrate [TiO(NO₃)₂] was obtained by reaction of TiO(OH)₂ with nitric acid. Finally, the aqueous solution containing titanyl nitrate [TiO(NO₃)₂] and a fuel, glycine, were mixed and combusted to obtain the nano-sized titania. The optimum conditions obtained by this method are as follows (based on 1 mol of TiO₂ per batch): concentration of HPC, 0.053 mg cm^?3; mole ratio of Ti:H₂O:IPA, 1:4:10; hydrolysis time, one hr; the amounts of HNO₃ and glycine are 10 ml and 0.5 g, respectively; nitrated temperature, 298 K and nitrated time, 2 h. TiO₂ nanocrystalline (～15 nm) with high BET surface area (350 m² g^?1) and narrow band gap energy (2.7 eV) were thus obtained.     

Optimization of experimental conditions based on Taguchi robust design for the preparation of nano-sized TiO2 particles by solution combustion method

This investigation was aimed at preparing nanocrystalline TiO₂ powder by solution combustion method, and searching the optimum preparing conditions by employing Taguchi robust design method. Taguchi robust design method with L₁₈ orthogonal array was implemented to optimize experimental conditions for preparing nano-sized titania particles. Titanium IV n-butoxide was hydrolyzed to obtain titany1 hydroxide [TiO(OH)₂], and titanyl nitrate [TiO(NO₃)₂] was obtained by reaction of TiO(OH)₂ with nitric acid. Finally, the aqueous solution containing titanyl nitrate [TiO(NO₃)₂] and a fuel, glycine, were mixed and combusted to obtain the nano-sized titania. The optimum conditions obtained by this method are as follows (based on 1 mol of TiO₂ per batch): concentration of HPC, 0.053 mg cm⁻³; mole ratio of Ti:H₂O:IPA, 1:4:10; hydrolysis time, one hr; the amounts of HNO₃ and glycine are 10 ml and 0.5 g, respectively; nitrated temperature, 298 K and nitrated time, 2 h. TiO₂ nanocrystalline (∼15 nm) with high BET surface area (350 m² g⁻¹) and narrow band gap energy (2.7 eV) were thus obtained.     

Barium titanate characterization by differential scanning calorimetry

Differential scanning calorimetry (DSC) was used to characterize barium titanate formed after decomposition of barium titanyl oxalate. Three different methods of the oxalate precipitation reaction were used to prepare barium titanyl oxalate which after calcinations result in barium titanates with different barium to titanium ratio (A/B). It appears that two factors have effect on Curie temperature: barium to titanium ratio and mechanical stress introduced by milling.     

The synthesis and structure of [Er(terpy)(NO3)3·(C2H5OH)]; an example of preference for monodentate over bidentate coordination for the nitrate group

Erbium is nine-coordinate in [Er(terpy)(NO₃)₃·(C₂H₅OH)], which contains two bidentate and one monodentate nitrate groups as well as a coordinated ethanol molecule.     

Phase development of barium titanate from chemically modified-amorphous titanium (hydrous) oxide precursor

A synthesis procedure for barium titanate involving a chemically modified titanium precursor has been developed. Using a titanium isopropoxide precursor modified with acetylacetone and barium acetate, coprecipitated gels were obtained by addition to a KOH solution. Direct precipitation of cubic BaTiO₃ from such precursor suspensions was obtained under hydrothermal conditions. The pH value was found to be a critical reaction parameter such that production of phase pure BaTiO₃ required high pH (>13.0), a finding consistent with thermodynamic predictions of the Ba–Ti–H₂O stability system and prior hydrothermal syntheses. It was determined that phase-pure barium titanate can be synthesized at temperatures as low as 50 °C and that higher reaction temperatures accelerate the crystallization process. The particle size of the synthesized powder ranged from 50 to 350 nm for the synthesis conditions explored in the current work.. It was demonstrated that particle size can be controlled by proper selection of the hydrothermal synthesis conditions such as reaction concentration, temperature, and time. The chemically modified synthesis produces barium titanate more rapidly at lower reaction temperatures than previously reported for similar syntheses.     

Synthesis of Nb-doped SrTiO3 by a modified glycine-nitrate process

The objective of the present investigation was to develop a technique to synthesize submicronic particles of Nb-doped strontium titanate with a homogeneous composition. This was achieved by a modified glycine-nitrate process, using Ti-lactate, Nb-oxalate, and Sr(NO₃)₂ as starting materials. A combination of both citric acid and glycine was needed in order to integrate the useful features of both complexation and combustion natures of citric acid and glycine, respectively. The amount of citric acid, glycine, and nitrates in the starting solution, as well as the source for extra nitrates, and the uniformity of heating during the thermal dehydration step were found to have significant influence on the final phase purity of the material. Calcination at 1100 °C in 7% H₂ in N₂ produced single phase Nb-doped strontium titanate with grain sizes of about 100 nm in diameter on average.     

Preparation of Rutile Titanium Dioxide White Pigment by a Novel NaOH Molten‐Salt Process: Influence of Doping and Calcination

Rutile titanium dioxide (TiO₂) white pigment is prepared by a novel NaOH molten‐salt process. Titanium slag is decomposited by NaOH molten salt to obtain sodium titanate which is then converted into hydrate titanium dioxide (H₂TiO₃) through acid dissolution and hydrolysis. Finally, TiO₂ white pigment is prepared by H₂TiO₃ doping and calcinations. H₂TiO₃ prepared by this innovative method is characterized and the influencing factors of doping and calcination of H₂TiO₃ on pigmentary properties of TiO₂ are investigated. H₂TiO₃ with certain characteristics could be prepared through the controlled hydrolysis step in the NaOH molten‐salt process. Good pigmentary properties of rutile TiO₂ white pigment are achieved by doping with suitable amounts of K₂O, P₂O₅, Al₂O₃, and rutile nuclei, thereby approaching the quality of the commercial TiO₂ pigment standards.     

Mechanochemical route for synthesizing nitrate form of layered double hydroxide

This paper introduces a mechanochemical process for synthesizing a nitrate compound, Mg-Al-(NO₃) (Mg:Al = 3:1), which is a layered double hydroxide (LDH) from three kinds of starting materials, Mg(OH)₂, Al(OH)₃ and Mg(NO₃)₂.6H₂O. The operation was attempted by one-and two-step milling operations, and the former is to grind the three kinds of samples simultaneously, while the latter is to mill two kinds, Mg(OH)₂ and Al(OH)₃, followed by further milling with Mg(NO₃)₂.6H₂O. Characterizations by XRD, FT-IR, and TG-DTA indicate that the latter step operation is superior to the former one in terms of the formation of the target material, nitrate form of LDH. This form could be taken as a potential candidate for slow-release fertilizer, where the release of the nitrate from the synthesized LDH has been held back due to the intercalation into the LDH structure.     

Solution combustion synthesis of metal nanopowders: Copper and copper/nickel alloys

Based on a general methodology for the preparation of metal–nanopowders by solution combustion synthesis (SCS), the reaction pathways for SCS of pure copper and copper–nickel alloy nanopowders are investigated. It is confirmed that the necessary condition for SCS of metals in a metal‐nitrate oxidizer–glycine system is the property of the oxidizer to decompose with formation of HNO₃ species. In this case, for compositions with excess of glycine, a hydrogen reducing atmosphere develops in the reaction front, leading to the formation of reduced metals. The proposed reaction pathways are supported by X‐ray diffraction analysis of the quenched samples and DTA–TGA studies of the Cu(NO₃)₂·6H₂O–glycine and Ni(NO₃)₂·6H₂O/Cu(NO₃)₂·6H₂O–glycine systems. The results show that the formation of Cu₂O and CuO oxide phases takes place at early stages in the reaction front followed by their reduction to pure Cu phase in the postcombustion zones. However, in a Cu–Ni alloy, a fraction of intermetallic Cu–Ni phase appeared directly in the combustion front, whereas the rest of the oxygen‐free alloy formed through reduction of oxide phases. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Preparation of a new type of half-sandwich (alkoxylalkylcyclopentadienyl)titanium trichloride complex and X-ray structural characterization of (CH3OCH2CH(CH3)C5H4)TiCl3

New substituted alkoxylalkylcyclopentadienyl titanium trichloride complexes, CH₃OCH₂CH(CH₃)C₅H₄TiCl₃ (3), CH₃OCH(CH₃)CH₂C₅H₄TiCl₃ (4) and CH₃OCH₂CH₂CH₂C₅H₄TiCl₃ (5) have been synthesized and 3 has been studied by X-ray diffraction. The crystal structure of 3 shows that there is an intramolecular coordination between the ethereal oxygen atom in the side chain on the Cp ring and the titanium atom with an average Ti–O bond length of 2.24 Å. Due to steric limitation around the coordination sphere of titanium, the oxygen atoms in the side chain in complexes 4 and 5 do not coordinate with the central metals.     

Preparation of Semiconducting Titanates by Chemical Methods

Semiconducting barium titanate has been prepared both by coprecipitating the lanthanum in the preparation of barium titanyl oxalate and by precipitation of lanthanum hydroxide in a slurry of the titanate. Partial substitution of strontium or lead for barium and zirconium for titanium has also been achieved using this oxalate process. The electrical conductivity of these materials was measured and is discussed. The effect of excess titanium on the electrical properties was also determined and an excess of 1 to 2 mole % was found to raise the positive temperature coefficient under the firing conditions employed.     

Polymérisation des oléfines par le système TiO2 chloré – alcoyle-aluminium

A superficial chlorination of titanium dioxide leads, combined with Al(C₂H₅)₂Cl, to a moderately active catalyst for the ethylene polymerization. The chlorination may be done using Al(C₂H₅)₂Cl only. The polymer remains strongly attached to the surface of the solid and cannot be extracted. The polymerization, although limited to very low conversion, causes a neat agglomeration of the TiO₂ grains.     

The use of plastic waste as carbon raw materials to obtain TiC-based powders

Plastic pollution is one of the most pressing environmental problems, and a huge amount of effort and money is directed towards solving it. The existing processing methods are ineffective. The main component of all plastic materials (C_xH_y) is carbon. High-purity fine titanium carbide was obtained using plastic waste (polyethylene terephthalate – C₁₀H₈O₄) as a carbon raw material. Combustion processes, phase composition and structure of the obtained materials were studied. A probable mechanism for the formation of titanium carbide during the combustion of the (Ti + C₁₀H₈O₄) mixture was proposed. During the synthesis, polyethylene terephthalate decomposes into carbon, hydrogen and oxygen. Carbon and oxygen react with titanium and form titanium oxycarbide. Titanium oxycarbide is saturated with carbon to form titanium carbide and carbon dioxide. The remaining hydrogen and carbon dioxide are released from the synthesis products, which leads to self-purification of the synthesis products. The obtained results will create the basis for the development of a fundamentally new, cost-effective technology for recycling plastic waste into carbides and carbide-containing materials.     

Selective synthesis of TiO2 nanopowders

Nanosized anatase, rutile, brookite, and mixtures of these materials taken in different ratios are synthesized using the detonation method with variations in the densities and ratios of explosives composed of the TiO₂ precursor, NH₄NO₃, and C₃H₆N₃(NO₂)₃. It is shown that the phase composition, the phase content, and the average particle size of TiO₂ nanopowders depend on the composition of the explosive mixtures and their densities. When the weight ratio between the C₃H₆N₃(NO₂)₃ compound and the TiO₂ precursor lies in the range 0.695–1.270, the average size of rutile particles is larger than that of anatase particles by a factor of approximately two.     

Synthesis of nano-crystalline NiO-YSZ by microwave-assisted combustion synthesis

Nano-crystalline NiO-YSZ composite powders have been successfully prepared by microwave-assisted combustion of a gel derived from an aqueous solution containing ZrO(NO₃)₂·6H₂O ,Y(NO₃)₃·6H₂O, Ni(NO₃)₂·6H₂O and glycine. The as-prepared powders were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. It was found that the process took only a few seconds to obtain NiO-YSZ composite powders. The as synthesized composite powder was a homogeneous mixture of YSZ, NiO and Ni phases with crystallite size of 24.2, 33.6 and 25.3 nm respectively.     

Combustion synthesis of PZN-10PT nanopowders

Discussed is the influence of the fuel and water employed in combustion synthesis of single-phase (perovskite) PZN-10PT nanopowder with an x = 0.10 composition. Pb(NO₃)₂, Zn(NO₃)₂ · 6H₂O, (NH₄NbO(C₂O₄)₂), and C₈H₂₀O₄Ti were used as cation precursors while urea, glycine, glycine/urea (50/50 ratio), and tetraformal triazine (TFTA), as fuels. Two sets of precursors (denoted as set-1 and set-2) were used with each of these fuels, and four different fuels: without and with the addition of 250 mL of water. The results indicated that the highest percentage of perovskite phase in the PZN-10PT nanopowders was obtained using an urea/glycine mixture as a fuel. When the urea/glycine mixture was added to the solution containing cations precursors, the two fuels form a gel in aqueous solution, this gel contributes not only to obtain homogeneously mixed in the starting material but also aids explosive combustion leading to a high-temperature reaction within a shorter period of time, which is a condition that favors the formation of metastable PZN-10PT nanopowders.     

Homogeneous reduction of aromatic nitrocompounds by a triphenylphosphine complex of palladium

The complex Pd₂(PPh₃)₂Cl₄ has been used as a homogeneous catalyst for the reduction of C₆H₅NO₂ and p-ClC₆H₄NO₂ in basic ethanol. A reaction intermediate [Pd(PPh₃) (C₆H₅NO₂)Cl₂] has been isolated and characterised. Reduction of C₆H₅NO₂ produced aniline (75%), azobenzene (5%) and azoxybenzene (15%) under conditions of atmospheric pressure, while under conditions of high pressure the reduction product contained aniline (95%) only. The yield of p-ClC₆H₄NH₂ was highest (75%) at normal pressure and decreased with increasing pressure.     

Modelling of NOx adsorption over NOx adsorbers

Modelling of the phenomena involved during the adsorption of NO_x on NO_x trap catalysts was developed. The aim of the model is the prediction of the quantity of stocked barium nitrate as well as the emissions of NO and NO₂, as a function of time and temperature. The mechanism of the process is sounded on the adsorption of gas species (NO, NO₂, O₂) on platinum sites, equilibrium reaction between adsorbed species followed by the formation of Ba(NO₃)₂. This formation of barium nitrate is limited by the thermal decomposition reaction which liberates NO in the gas phase. The kinetic constant of decomposition of barium nitrate was determined by temperature programmed thermogravimetry on pure Ba(NO₃)₂, using the method of Freeman and Carroll. Other kinetic constants bound to the mechanism were estimated by fitting the results of the model to experimental results.The mechanism was validated for various values of the molar fraction of O₂, the molar fraction of NO and various values of the NO/NO₂ ratio in the gas entering the reactor. It was also tested with different catalyst compositions (variation of the platinum and BaO concentrations). The importance of oxygen in the process was clearly demonstrated as well as the promoting role of NO₂.     

NO Oxidation Inhibition by Hydrocarbons over a Diesel Oxidation Catalyst: Reaction Between Surface Nitrates and Hydrocarbons

Abstract  

C₃H₆ oxidation over a Pt/Al₂O₃ catalyst with or without NO _x present was investigated, and the reaction mechanism was studied by diffuse reflectance infrared spectroscopy (DRIFTS). C₃H₆ oxidation is inhibited by the presence of NO, and vice versa, and data indicate that adsorbed NO _x can react with gas phase C₃H₆. DRIFTS results confirm the reaction between C₃H₆ and nitrates, which are formed during NO _x adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C₃H₆ oxidation in the presence of NO _x , namely, nitrates acting as oxidants. Using NO₂ instead of NO, or using a high NO _x /C₃H₆ ratio, which is beneficial for nitrate formation, favors this nitrate reaction pathway.     

Contribution of (NO3 −)surf Reduction to the Overall Mechanism of H2-Promoted n-C6H14-DeNOx Over Ag/Al2O3

Transient response experiments indicated that H₂-promoted n-C₆H₁₄-SCR over Ag/Al₂O₃ has a significant contribution from the pathway proceeding through the formation of surface nitrate complexes (NO₃ ^?)_surf followed by their reduction. The rate of (NO₃ ^?)_surf reduction by 300 ppm C₆H₁₄ in the presence of 1,000 ppm H₂ is virtually identical to the rate of steady-state H₂-promoted n-C₆H₁₄-SCR, while surface nitrate species reveal their inertness with respect to 300 ppm n-C₆H₁₄ only. Transient response experiments and temperature programmed desorption indicate that (NO₃ ^?)_surf is readily transformed by NO or H₂ to the reactive (NO₂ ^?)_surf complexes. The latter are further reduced by n-hexane in the presence of H₂.