Characterization of zirconium sulfate supported on TiO2 and activity for acid catalysis

A series of Zr(SO₄)₂/TiO₂ catalysts were prepared by impregnation of powder TiO₂ with an aqueous solution of zirconium sulfate. No diffraction line of zirconium sulfate was observed up to 30 wt%, indicating good dispersion of Zr(SO₄)₂ on the surface of TiO₂. The high catalytic activities of Zr(SO₄)2/TiO₂ for both 2-propanol dehydration and cumene dealkylation were related to the increase of acidity and acid strength due to the addition of Zr(SO₄)₂. Zr(SO₄)₂/TiO₂ containing 25% zirconium sulfate and calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for these reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. This paper is dedicated to Professor Hyun Ku Rhee on the occasion of his retirement from Seoul National University.     

Lignin–silica hybrids as precursors for silicon carbide

Lignin, prepared by digesting cedar with acetic acid, and tetraethoxysilane have been allowed for a sol–gel reaction in tetrahydrofuran using H₂SO₄ as catalyst to yield lignin–SiO₂ hybrids in the bulk gel form. The solid-state ¹³C nuclear magnetic resonance spectra of the hybrids and products formed solely from the lignin under the acidic conditions revealed that the lignin underwent crosslinking during the sol–gel reaction. The degree of crosslinking increased with an increasing amount of H₂SO₄. The powdered hybrids have been heated at 1500°C in Ar for carbothermal reduction, resulting in the formation of SiC powders. The lignin-to-tetraethoxysilane mixing ratio of the starting solutions varied free carbon content in the SiC powders. In addition, the amount of carbonaceous residue formed from the lignin upon heating depended on the degree of crosslinking of the lignin. Thus, to adjust the amounts of both the lignin and H₂SO₄ was necessary for producing the hybrids suitable for precursors for SiC powders with high purity. Critical adjustment of the amounts led to the formation of SiC powders with a free carbon content of 0.57 wt %, implying that the lignin is a beneficial carbon source for the production of SiC powders by the hybrid route. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1321–1328, 1999     

Methane combustion on sol–gel Rh/ZrO2–SiO2 catalysts

Rh/ZrO₂–SiO₂ catalysts prepared by impregnation of mixed ZrO₂–SiO₂ oxides obtained by using the sol–gel method were characterised and used in the combustion of CH₄. It was found that the specific area and porosity depend strongly on the pH of gelation. Two different Zr precursors were used: Zr(acac)₄ and Zr alkoxide. When the former precursor is used, no significant changes in the surface area are detected, however, important changes in pore size distribution are observed. In those samples prepared from Zr alkoxide, both the surface area and the porosity change significantly. No important changes in rhodium dispersion were observed by TEM, in agreement with XPS results. On the contrary hydrogen chemisorption results indicate that the hydrogen uptake of the sulfated samples drops drastically compared with those in which sulfate ions are absent. This behaviour has been attributed to a poisoning of rhodium particles by sulfide species produced by reduction of sulfate ions, as was revealed by TPR. The catalytic activity in the methane combustion is affected by the presence of chloride ions, which induce an inhibitory effect on the combustion. Additionally, the presence of micropores also decreases the activity due to diffusional limitations. © 1999 Society of Chemical Industry     

Role of dual dopants in highly ordered crystalline polyaniline nanospheres: Electrode materials in supercapacitors

Aniline is oxidized by ammonium persulfate oxidant with a weak organic acid, 1,3‐(6,7)‐napthalene trisulfonic acid (NTSA), via an aqueous polymerization pathway to polyaniline (PANI) salt. The effects of the sodium lauryl sulfate surfactant, mineral acid [sulfuric acid (H₂SO₄)], and a combination of surfactant with mineral acid in the aniline polymerization reaction are also carried. These salts were designated as PANI–NTSA–dodecyl hydrogen sulfate (DHS), PANI–NTSA–H₂SO₄, and PANI–NTSA–DHS–H₂SO₄, respectively. Interestingly, PANI–NTSA–DHS showed a highly ordered crystalline sample with a nanosphere morphology. These PANIs were used as electrode materials in supercapacitor applications. Among the four salts, the PANI–NTSA–DHS–H₂SO₄ material showed higher values of specific capacitance (520 F/g), energy (26 W h/kg), and power densities (200 W/kg) at 0.3 A/g. Moreover, 77% of the original capacitance was retained after 2000 galvanostatic charge–discharge cycles with a Coulombic efficiency of 98–100%. PANI–NTSA–DHS–H₂SO₄ was obtained in excellent yield with an excellent conductivity (6.8 S/cm) and a thermal stability up to 235°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42510.     

Efficient Esterification of Fatty Acids with Alcohols Catalyzed by Zr(SO4)2 · 4H2O Under Solvent-Free Condition

Zirconium sulfate (Zr(SO₄)₂ · 4H₂O) was an efficient catalyst for the esterification of fatty acids and alcohols under solvent-free condition. The esterification of fatty acid with branched alcohols using Zr(SO₄)₂ · 4H₂O catalyst gave a good yield of the corresponding ester. The zirconium sulfate Bronsted acid site was suggested to be the catalytically active species in this reaction. In addition, Zr(SO₄)₂ · 4H₂O compound is a potential green catalyst due to its high catalytic activity and low toxicity. This compound is also cost effective, easy to handle, is easily recovered by simple filtration and can be recycled for further reactions.     

Washcoating method for Pd/γ-Al2O3 deposition on metallic foams

A method for coating open celled metal foams with a thin layer of Pd–Al₂O₃ was developed. The method makes use of a sol–gel of pseudobohemite as a precursor of γ-Al₂O₃ to fill the porous structure by percolation whilst the excess of material is flushed away with an air jet. The influence of solid content, acid content and ageing on the sol–gel rheological behaviour was studied to find a sol–gel dispersion with an appropriate viscosity whose deposition resulted in a 20 μm thick coating layer. Foam samples of different nominal porosities (10, 20 and 40 PPI) were coated with this method and activated with palladium using a wet impregnation procedure with loadings of 3% (w/w) palladium on the alumina.As an alternative approach, dry impregnation of γ-Al₂O₃ with palladium was performed and a slurry was prepared adding water and nitric acid. The slurry was deposited by percolation through the foam structure. The coating quality was evaluated with adhesion tests and the activity of coated foams was measured by performing catalytic oxidation of CO in a 9 mm i.d. tubular reactor. Both methods produced highly active foams, resulting in light off temperatures between 175 and 250 °C depending on CO concentration. Moreover, the mass transfer controlled regime was achieved in all runs independently of the coating method. Nevertheless, conversions reached when the sol–gel dispersion was deposited and activated via wet impregnation were higher than the ones obtained with the coating method based on slurry deposition of active powders, indicating that the sol–gel deposition resulted in more uniform coating.     

Thermal stability of Pt particles of Pt/Al2O3 catalysts prepared using microemulsion and catalytic activity in NO–CO reaction

Sintering behaviors of the Pt particles of Pt/Al₂O₃ catalyst prepared using different preparation methods (microemulsion, sol–gel, and impregnation methods) were investigated. It was found that the catalyst prepared by microemulsion had a higher resistance to sintering than did the sol–gel and impregnation catalysts. To limit the sintering even more, the catalysts were pressed. The resistance to sintering in all the catalysts was improved by pressing. The pressed microemulsion catalyst was little deactivated in the NO–CO reaction by thermal treatment at 700 °C for 12 h, and had a high activity relative to that of the sol–gel and impregnation catalysts.     

Efficient and selective conversion of hexose to 5-hydroxymethylfurfural with tin–zirconium-containing heterogeneous catalysts

Efficient and selective production of 5-hydroxymethylfurfural (HMF) from the hexose is achieved in the presence of heterogeneous Sn-based catalyst. The mixed SnO₂–ZrO₂ is prepared from zirconium n-propoxide and different metal Sn precursors using Sol–gel method. The sulfated SnO₂–ZrO₂ (SO₄^2 −/SnO₂–ZrO₂) is obtained by the impregnation method with H₂SO₄ solution. All catalytic materials are detected with XRD, TG, SEM, TEM and BET techniques in order to reveal the physical properties and structures of these materials. When these materials were used in the dehydration of fructose, it was found that the suitable ratio of Sn/Zr is 0.5, and the catalytic activity of SO₄^2 −/SnO₂–ZrO₂ is higher than that of SnO₂–ZrO₂ where more than 75.0% yield of HMF was obtained for 2.5 h at 120 °C. The effects of reaction temperature and reaction time were also investigated. Moreover, the recycling experiment of catalyst shows that the catalytic activity can be almost kept unchanged after being used five times.     

Lamellar Inorganic Ion Exchangers. H+/M2+ (M=Ca,Cu) Ion Exchange in γ-Titanium Phosphate by Using Acetate Salts.

Exchange isotherms and pH curves at 25.0, 40.0, 55.0 and 80.0°C are obtained. The hydrolysis degree and the amount of metallic phosphate precipitated are determined. The evolution of the solids is followed by X-ray diffraction. The substitution increases with temperature, reaching at 80.0°C the 70% (Ca²⁺) and the 90% (Cu²⁺). The results are compared with those obtained by using (CaCl₂ + HCl), (CaCl₂ + Ca(OH)₂) or (CuSO₄ + H₂SO₄) solutions.     

Active sites on Pt containing sulfated zirconia

The influence of the Pt and sulfate concentration on the activity of Pt containing sulfated zirconia for n-heptane conversion was investigated. Pt was deposited on the support by impregnation and by photocatalytic deposition. The amount deposited was 2.5 and 0.4 wt% respectively. For comparison a hybrid catalyst consisting of sulfated zirconia and Pt on SiO₂ was prepared. As supports a commercial sulfated zirconia with a fixed sulfate concentration, a commercial and self synthesized Zr(OH)₄ were used. The sulfate content varied between 20 and 60% of a monolayer. The shifts to higher frequency in the IR spectra of CO adsorbed on Pt correlate with the increasing amounts of sulfates on zirconia and are attributable to the changes in the electron density of the supported metal, i.e. the electron deficiency of Pt increases with increasing concentration of acid sites. After activation in air and reduction in hydrogen two SO₂ peaks were detected by a temperature programmed heating procedure (TPE—temperature programmed evolution). The lower the desorption temperature of the first SO₂ peak, the higher the activity. The shift to lower temperature is connected with a higher Pt and sulfate concentration, furthermore with the proximity of the metal to acid sites. The catalysts with a low sulfate concentration possess only Lewis acid sites and are inactive for n-heptane conversion. At higher sulfate concentration, Br?nsted acid sites are present and the catalysts are active. The concentration of these acid sites is related to the concentration of sulfates, which desorb at lower temperature. Dedicated to Professor Konrad Hayek.     

Synthesis of Camphene by α-Pinene Isomerization Using W2O3–Al2O3 Catalysts

W₂O₃–Al₂O₃ catalysts prepared by “sol–gel” and impregnation methods were characterised by XRD, FTIR and nitrogen adsorption. Both catalysts were tested in the isomerization of α-pinene in a batch reactor at atmospheric pressure and 150 °C. Conversion of α-pinene and selectivity to camphene was superior for the “sol–gel” catalyst than that observed for the impregnated catalyst.     

Colloidal Sol–Gel Synthesis and Photocatalytic Activity of Nanoparticulate Nb2O5 Sols

A detailed study of a novel synthesis via colloidal sol–gel route for obtaining nanoparticulate Nb₂O₅ was performed. Parameters such as temperature and H⁺:Nb⁵⁺ and Nb⁵⁺:H₂O molar ratios were controlled in order to determine the best conditions of synthesis. Moreover, particle size distribution, zeta potential, structure by X‐ray diffraction, and the photocatalytic activity of the particulate sols were also evaluated. The obtained results indicate that the colloidal sol–gel synthesis is a good alternative for obtaining Nb₂O₅ either as stable nanoparticulate sol or as a nanosized powder. Nb₂O₅ amorphous nanoparticles with an average size of 20 nm were obtained by controlling the synthesis variables. The heat‐treatment process allowed the formation of Nb₂O₅ with orthorhombic structure that transforms at higher temperatures to monoclinic phase. The highest photocatalytic activity was observed under λ = 365 nm, the smallest UV energy used in the experimental tests.     

Chemical additives for calcium sulfate scale control

The morphology of calcium sulfate phases precipitated from sea water over the temperature range 125–150°C has been investigated and the effect of chemical additives on morphology is discussed. Effective additives appear to adsorb on nuclei in the liquid to slow crystal growth by displacing SO⁼₄ and attaching to Ca⁺⁺. The effectiveness of PO₃H^- and CO₂H suggests that adsorption may involve OH^- bonding to calcium ions on the growth face.     

Steam Reforming of Bio‐Oil for Hydrogen Production: Effect of Ni‐Co Bimetallic Catalysts

Various Ni‐Co bimetallic catalysts were prepared by incorporating sol‐gel and wet impregnation methods. A laboratory‐scale fixed‐bed reactor was employed to investigate their effects on hydrogen production from steam reforming of bio‐oil. The catalyst causes the condensation reaction of bio‐oil, which generates coke and inhibits the formation of gas at temperatures of 250 °C and 350 °C. At 450 °C and above the transformation of bio‐oil is initiated and gaseous products are generated. The catalyst also can promote the generation of H₂ as well as the transformation of CO and CH₄ and plays an active role in steam reforming of bio‐oil or gaseous products from bio‐oil pyrolysis. The developed 3Ni9Co/Ce‐Zr‐O catalyst achieved maximum hydrogen yield and lowest coke formation rate and provided a better stability than a commercial Ni‐based catalyst.     

Preparation and characterization of the continuous titanium-doped ZrO2 mesoporous fibers with large surface area

The continuous titanium-doped ZrO₂ mesoporous fibers with a large surface area (190 m² g^?1, TZ50-400) have been prepared by the sol–gel method coupled with the chemical template route. In the formation process, the self-induced acid environment of ZrOCl₂·8H₂O in ethanol solution was utilized to avoid a rapid hydrolysis process and the viscous sol precursors were successfully obtained for spinning fibers. X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectra were used to study the chemical environment of surface Ti(IV) and Zr((IV)) ions. The findings disclose that the partial Ti atoms (less than 30 %) enter into the ZrO₂ lattice and occupy the positions of Zr atoms, while the excess Ti atoms construct the linear Ti–O–Ti chains inside the extra framework, being favorable to prevent the collapse of meso structure.     

Mechanistic study of hafnium and zirconium extraction with organophosphorus extractants

Research on the purification of Zr has increased in the last few decades and although effective processes have been developed, little is known about the mechanism of Hf and Zr extraction; particularly, at low acid concentrations. This study’s aim was to determine the influence of alterations in alkyl substituents on the extraction mechanism of Hf and Zr from sulfate media. Seven organophosphorus extractants (Dio-PA, TPPA, DPPA, TPPO, TPPS, D2EHPA and Ionquest 801) were screened with four of them (Dio-PA, DPPA, D2EHPA and Ionquest 801) resulting in promising extraction results. This was attributed to the activity of the acidic hydroxy phosphinyl (=P(O)OH) group which is responsible for the dimerization and cation exchange properties of the extractant. The extractant and hydrogen ion stoichiometries involved in the extraction mechanism were determined for these four extractants by slope analysis from extractant- and acid-variation experiments. It was found that Dio-PA, D2EHPA, and Ionquest 801 extract via a cation-exchange mechanism, according to [M(OH)₂]²⁺ + 2 HA ? M(OH)₂A₂ + 2 H⁺. In contrast, the extraction with DPPA was best described by a solvated cation exchange (SCE) mechanism, according to [M(OH)]³⁺ + 6 HA ? M(OH)A₃.3HA + 3 H⁺. It was concluded that the presence of electron-withdrawing substituents produced softer Lewis base extractants, which favored the extraction of Hf over Zr from acidic sulfate media.     

The influence of iron content on the promotion of the zircon structure and the optical properties of pink coral pigments

A sol–gel reaction starting from Si and Zr alkoxides, in water-ethanol mixtures, was employed to obtain iron doped zirconium silicate powders (zircon). The starting amount of the ferric salt in the sol–gel reacting mixture was varied in order to obtain Fe₂O₃/Zr molar ratios in the range 0.7–10%. The products of the sol–gel reaction were calcined in the range 800–1300 °C. X-ray diffractograms, EDX analyses and diffuse reflectance spectra were obtained and analysed for all the calcined powders; the colour of the pigments was characterised on the grounds of the CIE (Commission Internationale de l’Eclairage) standard procedure (CIE L¹a¹b¹ measurements). Results from the structural and spectral characterisations are examined and cross-compared to produce a consistent picture of the role played by iron on the promotion of the zircon lattice and on the optical properties of the reaction products.     

Extraction of Zirconium and Hafnium in Polyethylene Glycol‐Based Aqueous Biphasic System

Abstract

The behavior of zirconium and hafnium in PEG 2000‐Na₂SO₄‐HCl aqueous biphasic system has been investigated. The dependences of HCl concentration (0.185–0.55 M), extraction temperature (298–318 K), and extraction time (5–120 min) on distribution ratios have been determined. Extraction of this metals in PEG 2000‐Na₂SO₄‐H₂SO₄ and PEG 2000‐Na₃Cit‐HCl systems has been also studied. The sulfate and citrate complexes of Zr and Hf prefer salt‐rich phase in contrast to chloride complexes which pass into PEG rich phase in about 50% (w/w) to the greatest degree in room temperature and at short extraction time. The increase of distribution ratios (D*_Zr=3.75, D*_Hf=4.31) was observed after addition of water soluble organic ligand ‐ tiron (4,5‐dihydroxy‐m benzenedisulfonic acid disodium salt). The results obtained in studied conditions are not very useful for the separation of zirconium and hafnium.     

The Hafnium-Selective Extraction Fom a Zirconium(Hafnium) Heptafluoride Ammonium Solution Using Organophosphorus-Based Extractants

ABSTRACT

The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHPA was evaluated for the selective extraction of Zr and Hf from an (NH₄)₃Zr(Hf)F₇ acidic solution using both dispersive and pertraction solvent extraction (SX). A stock solution of (NH₄)₃Zr(Hf)F₇ was dissolved in either HCl or H₂SO₄ (0.1–8 M). The following extraction variables were investigated: type and concentration of the acidic solution, the contact time, and extractant to metal ratio. Subsequently, the stripping was investigated using (NH₄)₂CO₃, CaCl₂, H₂SO₄ and C₂H₂O₄ in the concentration ranges of 0–2 M. During extraction, scrubbing and stripping using D2EHPA, CaCl₂ and C₂H₂O₄, the Zr purity was increased from 97.2% to 99.0%. When extracting from 4 M H₂SO₄ with 9 wt% D2EHPA, a Hf selectivity of 32% was observed where after stripping with C₂H₂O₄ resulted in a 98.7% recovery of Zr. With 1.2 M CaCl₂ as stripping liquor, almost no Hf and 75% Zr stripping was obtained. During the pertraction 72% Hf and 44% Zr extraction was achieved after 180 min when extracting with 9 wt% D2EHPA from 4 M H₂SO₄. Pertraction based stripping with 1.2 M C₂H₂O₄ yielded 75% of both Zr and Hf, while stripping with 2 M CaCl₂ resulted in 58% Hf stripped with almost no Zr stripping.     

Characterization and reactivity of VMgO catalysts prepared by wet impregnation and sol–gel methods

This paper reports the study of physicochemical, surface, and catalytic properties of two series of VMgO catalysts prepared by two different methods: wet impregnation and sol–gel. The characterizations of the elaborated materials were performed using N₂-sorption (Brunauer, Emmett and Teller (BET)), X-ray diffraction, Raman, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analyses. The catalytic properties of the elaborated materials were investigated in the isopropanol decomposition reaction to determine their acid–base character and in the selective oxidation of n-butane to evaluate their dehydrogenation properties. The preparation method and vanadium content strongly affected the properties of our materials. The sol–gel method leads to smaller crystallite size, higher specific surface area, and uniform particle distribution compared to the impregnation one. Both impregnation and SG solids promote the formation of acetone, which is related to the presence of strong basic sites (O^2? species) on the catalytic exposed surface. The more pronounced basic character was obtained through the SG samples. The sol–gel samples exhibited the highest catalytic activity and C4-olefin selectivity in the partial oxidation of n-butane. Whatever the preparation procedure, the nature of surface oxygen species plays an important role in the orientation of catalytic performances.