One-step preparation of manganese-, iron-, and aluminum-promoted sulfated zirconias for reaction of butane to isobutane

Highly active superacids of Mn-, Fe-, and Al-sulfated ZrO₂'s for the isomerization of butane to isobutane were obtained by exposing zirconia gel to aqueous solutions of 0.05 M MnSO₄, 0.25 M FeSO₄, and 0.5 M Al₂(SO₄)₃ followed by calcining in air at 700, 600, and 675°C, respectively. The catalysts were much more active than the superacid of sulfated zirconia, the temperature difference to show the same conversion (20%) between the catalysts and sulfated zirconia being 85, 77, and 85°C for the Mn-, Fe-, and Al-catalysts, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Co-doped MnCeOx/ZrO2 catalysts for low temperature selective catalytic reduction of NO

Co-doped MnCeO_x/ZrO₂ catalysts were synthesized by impregnation method and their low temperature deNOx performance were evaluated. The physicochemical properties of the catalysts were studied. The results showed that the doped Co could promote the deNOx performance of MnCeO_x/ZrO₂ significantly, and the doped catalyst with the Co/Mn molar ratio of 1:2 possessed the best catalytic performance. Compared with pure MnCeO_x/ZrO₂ catalyst, the deNOx efficiency of the optimal 1Co₂MnCeO_x/ZrO₂ was higher to 93% at 100 °C, improved nearly by 17%. The complete removal of NO was achieved at the temperature range of 120–250 °C. The promoted catalytic performance of Co-doped MnCeO_x/ZrO₂ catalyst was mainly attributed to the improvement of the catalyst support structure and surface acidity by Co. The catalytic reaction of NO with NH₃ over 1Co2MnCeO_x/ZrO₂ catalyst follows both Eley–Rideal mechanism and Langmiur–Hinshelwood mechanism.

     

The transformations of toluene on alumina and bifunctional catalysts

The activity of Pt, Rh, and Ni catalysts deposited on Al₂O₃ and tungsten-containing catalysts 20% H₄SiW₁₂O₄₀/ZrO₂ and 15% WO_x/ZrO₂ in the hydrogenation of toluene and toluene ring opening and isomerization in the presence of hydrogen was studied. Under experimental conditions (160–360°C, 2.2 MPa), the main reactions on Rh/Al₂O₃ were the hydrogenation of toluene into methylcyclohexane, hydrogenolysis into isoheptanes, and hydrocracking into alkanes C₁–C₆. On Pt, Rh, and Ni catalysts on carriers with strong acid properties, the isomerization of the six-membered into five-membered ring followed by hydrogenolysis (hydrocracking) of alkylcyclopentanes occurred. The yield of heptane isomers, however, did not exceed 13%. The activity of Pt and Rh catalysts on a high-acidity carrier (WO_x/ZrO₂) in hydrocracking was much higher than that of catalysts based on deposited heteropoly acid. The yields of hydrogenolysis (hydrocracking) products on Ni/WO_x/ZrO₂ were much lower than on Pt(Rh)/WO_x/ZrO₂. The highest yield of ring opening products (isoheptanes and n-heptane) was obtained with layered loading of two catalysts; it reached 58 wt % at 300°C and a 2.2 MPa pressure, which was 4.5 and 2 times higher than the yield obtained on Ni-Pt/WO_x/ZrO₂ and 2% Rh/Al₂O₃ catalysts. Hydrodemethylation was not the main direction of toluene transformations on any of the catalysts studied.     

Preparation and Catalytic Activity of a Novel Nanocrystalline ZrO2@C Composite for Hydrogen Storage in NaAlH4

Sodium alanate (NaAlH₄) has attracted intense interest as a prototypical high‐density hydrogen‐storage material. However, poor reversibility and slow kinetics limit its practical applications. Herein, a nanocrystalline ZrO₂@C catalyst was synthesized by using Uio‐66(Zr) as a precursor and furfuryl alcohol (FA) as a carbon source. The as‐synthesized ZrO₂@C exhibits good catalytic activity for the dehydrogenation and hydrogenation of NaAlH₄. The NaAlH₄‐7 wt % ZrO₂@C sample released hydrogen starting from 126 °C and reabsorbed it starting from 54 °C, and these temperatures are lower by 71 and 36 °C, respectively, relative to pristine NaAlH₄. At 160 °C, approximately 5.0 wt % of hydrogen was released from the NaAlH₄‐7 wt % ZrO₂@C sample within 250 min, and the dehydrogenation product reabsorbed approximately 4.9 wt % within 35 min at 140 °C and 100 bar of hydrogen. The catalytic function of the Zr‐based active species is believed to contribute to the significantly reduced operating temperatures and enhanced kinetics.     

Nonenzymatic glucose sensing at ruthenium dioxide–poly(vinyl chloride)–Nafion composite electrode

Development of nonenzymatic glucose sensors with high reproducibility and stability is an urgent need to reduce cost of regular diabetic monitoring. Here, we have fabricated ruthenium dioxide–poly(vinyl chloride)–Nafion (RuO₂–PVC–Nafion) composite for direct glucose sensing in sodium hydroxide and phosphate buffer nonenzymatically for the first time. The restricted activity of the RuO₂–PVC film electrode in alkaline pH is extended to neutral pH using Nafion as an outer membrane, which reduces the distance between Ru active sites by bridging effect and improves the electrode stability. The catalytic rate, measured in terms of change of RuO₂ resistance, is similar irrespective of the medium for the high temperature annealed RuO₂ (700 °C), whereas the low temperature annealed RuO₂ (300 °C) is highly sensitive for the change in the pH of the solution. This is revealed by observing large Michaelis–Menten kinetic constant K _M for the RuO₂ (700 °C) than the low temperature annealed RuO₂ (300 °C) due to effective increase in the catalytic active sites similar to oxygen evolution reaction. Contrast to this, the buffer solution does not influence significantly the apparent K _M observed for RuO₂ (300 °C) and has greater impact on the high temperature 500 and 700 °C annealed RuO₂ samples. Cyclic voltammetry, chrono amperommetry, and electrochemical impedance spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction techniques are used for characterization of the sensor behavior. The RuO₂–PVC–Nafion senses glucose selectively in the presence of potential interferences like fructose, galactose, mannose, sucrose, starch, uric acid, ascorbic acid, dopamine, and catechol in NaOH and phosphate buffer. Glucose sensing in the blood serum of the diabetic and nondiabetic patients is made. The results suggest that the RuO₂–PVC–Nafion is a promising candidate for the development of nonenzymatic glucose sensors.     

ZrO2- and Li2ZrO3-stabilized spinel and layered electrodes for lithium batteries

Strategies for countering the solubility of LiMn₂O₄ (spinel) electrodes at 50 °C and for suppressing the reactivity of layered LiMO₂ (M=Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn₂O₄ with colloidal zirconia (ZrO₂) dramatically improves the cycling stability of the spinel electrode at 50 °C in Li/LiMn₂O₄ cells. ZrO₂-coated LiMn_0.5Ni_0.5O₂ electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li⁰). The use of Li₂ZrO₃, which is structurally more compatible with spinel and layered electrodes than ZrO₂ and which can act as a Li⁺-ion conductor, has been evaluated in composite 0.03Li₂ZrO₃ · 0.97LiMn_0.5Ni_0.5O₂ electrodes; glassy Li_xZrO_2 + x/2 (0<x⩽2) products can be produced from colloidal ZrO₂ for surface coatings.     

Photodegradation of organic compounds using chromium oxide-doped nano-sulfated zirconia

ZrO₂ is considered a huge-gap semiconductor (band gap ≈ 5 eV). To improve the visible-light photocatalytic activities of ZrO₂, an efficient Cr, SO₄ ^2? co-doped ZrO₂ photocatalyst was synthesized by the simple impregnation method followed by calcination at different calcination temperatures (300, 400, 500, and 600 °C) for 3 h. The synthesized photocatalysts were characterized by x-ray diffraction, transmission electron microscopy analysis, scanning electron microscopy analysis, energy dispersive X-ray spectroscopy analysis, FT-IR spectroscopic technique, potentiometric titration and UV–Vis spectroscopy analysis. ZrO₂ co-doped with Cr and SO₄ ^2? shows more efficiency than SO₄ ^2?-doped ZrO₂ in several aspects like surface structure, decreasing electron–hole recombination and band gap energy. The photodegradation of methylene blue dye for SO₄ ^2?-doped ZrO₂ and Cr, SO₄ ^2?-co-doped ZrO₂ has been investigated. The photocatalytic reaction confirmed that the co-doped ZrO₂ photocatalyst showed higher photocatalytic activity than mono-doped ZrO₂.     

RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO₂-PVC film electrodes, fabricated using RuO₂ powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO₂-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO₂ (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO₂ (300°C)-PVC electrode. Also, RuO₂ (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO₂ (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K _M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO₂ powder samples.     

Promotional effect of acidic oxide on catalytic activity and N2 selectivity over CeO2 for selective catalytic reduction of NOx by NH3

The CeO₂, CeO₂‐ZrO₂ and CeO₂‐WO₃ catalysts were prepared by hydrothermal method and used to the selective catalytic reduction of NO_x by NH₃. The addition of ZrO₂ or WO₃ into CeO₂ was favorable for pore structure, and then improved the number of active sites. Besides, the introduction of ZrO₂ into CeO₂ could improve the Lewis acid sites while WO₃ could contribute to the generation of Brønsted and Lewis acid sites, which could improve the catalytic performance and N₂ selectivity. The CeO₂‐WO₃ catalyst exhibited optimal catalytic activity with above 90% NO_x conversion performance at 220–425 °C and approximately 100% N₂ selectivity at 150–425 °C.     

Microwave-assisted synthesis of organic–inorganic poly(3,4-ethylenedioxythiophene)/RuO2·xH2O nanocomposite for supercapacitor

An organic–inorganic poly(3,4-ethylenedioxythiophene) (PEDOT)/RuO₂·xH₂O nanocomposite (approximately 1 wt.% RuO₂) has been successfully prepared for the first time under microwave irradiation within 5 min with power 900 W via in situ chemical polymerization. The morphology and structure of the resultant material is characterized by transmission electron microscope and Fourier transform infrared. Moreover, the electrochemical properties of the synthesized nanocomposite can be controlled by adjusting the annealing temperature, which is definitely illustrated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectra. Electrochemical data have shown that the PEDOT/RuO₂·xH₂O nanocomposite annealed at 150 °C possesses the most favorable charge/discharge ability with a specific capacitance of 153.3 F g⁻¹ at a current density of 150 mA g⁻¹ and the high efficient utilization of PEDOT at various current densities. Furthermore, such composite has a less capacitance degradation of 23.8% after 1,000 continuous cycles. The improved electrochemical performance are mainly attributed to the large electroactive surface of nanocomposite and the existence of amorphous RuO₂·xH₂O particles as well as a synergistic effect of the polymer PEDOT and annealed RuO₂·xH₂O. Thus, the PEDOT/RuO₂·xH₂O nanocomposite annealed at 150 °C can act as a promising electroactive material for supercapacitor application.     

Physicochemical properties and mixed electronic and ionic conduction of composite ceramics in the system ZrO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

Composites ZrO₂-(Bi₂CuO₄+ 20 wt % Bi₂O₃) (50–80 vol % ZrO₂) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO₂ of a monoclinic modification, Bi₂CuO₄, and solid solution Bi_2?x Zr _x O_{3 + x/2} and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 10⁴ Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ～0.01 S cm^?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO₂ and 50 vol % (Bi₂CuO₄ + 20 wt % Bi₂CuO₄) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10^?8 mol cm^?2 s^?1, testifying that these materials may be used as gas-separating membranes.     

Facile synthesis of WOx/ZrO2 catalysts using WO3·H2O precipitate as synthetic precursor of active tungsten species

Zirconia-supported tungsten oxide (WO_x/ZrO₂) catalysts were successfully synthesized using a suspension containing amorphous hydrous zirconia precipitates [ZrO_x(OH)_4-2x·yH₂O]_n and tungstate monohydrate (WO₃·H₂O) precipitates. The procedure involved the dissolution of the WO₃·H₂O precipitate during the aging process with the release of oxyanion [WO₄]^2- species, interaction of this species with the surface of the [ZrO_x(OH)_4-2x·yH₂O]_n precipitate and, formation of active WO_x species after thermal treatment. Non-bridging hydroxyl (OH^?) groups present in the [ZrO_x(OH)_4-2x·yH₂O]_n precipitate act as an active agent for the WO₃·H₂O dissolution. N₂ physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction using hydrogen (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD), Fourier-transform infrared (FTIR) spectroscopy of adsorbed pyridine, and Raman spectroscopy were used to elucidate the catalyst structure–performance relationship. The catalytic activity was evaluated for the oxidative desulfurization (ODS) of a model fuel containing dibenzothiophene (DBT). For a fixed WO₃·H₂O content, longer aging times improved the catalyst activity, reaching a maximum when WO₃·H₂O was completely dissolved. The increase in surface area and formation of more active Zr-WO_x clusters and polytungstates are observed for the highest active catalysts. A synergetic effect between local Lewis and Brønsted acid sites seems to have contributed to the observed superior activity. The proposed strategy provides an efficient approach to produce active WO_x/ZrO₂ catalysts and may be applicable for designing other heterogeneous catalytic systems.     

Hydrogen production by aqueous phase reforming of sorbitol using bimetallic Ni–Pt catalysts: metal support interaction

Hydrogen was produced by Aqueous Phase Reforming (APR) of 10% (w/w) sorbitol using mono- and bi-metallic catalysts of Ni and Pt supported on alumina nano-fibre (Alnf), mesoporous ZrO₂ and mixed oxides of ceria–zirconia–silica (CZxS) with varying concentration of silica (where x is silica concentration). X-ray diffraction, TEM/EDS and temperature programmed reduction were also carried on these catalysts to study the surface properties. It was observed that co-impregnation of Pt and Ni in atomic ratio 1:12 increased the reducibility of Ni by forming an alloy. However, sequential impregnation of Ni followed by Pt does not form the bi-metallic particles to increase the Ni reducibility. Reduction peak of co-impregnated Ni–Pt/Alnf was found to be 270 °C lower than the sequentially impregnated Pt/Ni/Alnf. The presence of silica at high concentration in CZxS support decreased the reducibility of ceria by forming an amorphous layer on Ce_xZr_1?xO₂ crystals, which also decreased Ni reducibility. The rate of H₂ formation from aqueous phase sorbitol reforming was found to be highest for co-impregnated Ni–Pt catalysts followed by sequentially impregnated Pt/Ni and monometallic Ni catalyst. The H₂ activity decreased in the following order of the supports: Alnf > ZrO₂ > CZ3S > CZ7S.     

Physicochemical characteristic of neodymium oxide-based catalyst for in-situ CO2/H2 methanation reaction

Carbon dioxide emission to the atmosphere is worsened as all the industries emit greenhouse gases (GHGs) to the atmosphere, particularly from refinery industries. The catalytic chemical conversion through methanation reaction is the most promising technology to convert this harmful CO₂ gas to wealth CH₄ gas for the combustion. Thus, supported neodymium oxide based catalyst doped with manganese and ruthenium was prepared via wet impregnation route. The screening was initiated with a series of Nd/Al₂O₃ catalysts calcined at 400?°C followed by optimization with respect to calcination temperatures, based ratios loading and various Ru loading. The Ru/Mn/Nd (5:20:75)/Al₂O₃ calcined at 1000?°C was the potential catalyst, attaining a complete CO₂ conversion and forming 40% of CH₄ at 400?°C reaction temperature. XRD results revealed an amorphous phase with the occurrence of active species of RuO₂, MnO_2, and Nd₂O₃, and the mass ratio of Mn was the highest among other active species as confirmed by EDX. The ESR resulted in the paramagnetic of Nd³⁺ at the g value of 2.348. Meanwhile nitrogen adsorption (NA) analysis showed the Type IV isotherm which exhibited the mesoporous structure with H3 hysteresis of slit shape pores.     

Benzoylation of benzene and substituted benzenes catalyzed by superacid ZrO_2:H_2SO_4

Superacid ZrO_2:H_2SO_4 showed high activity in Friedel-Crafts benzoylation of benzeneand substituted benzenes such an chlorobenzene,toluene and 1,3,5-trimethylbenzene.Benzophenonesin 90-100% yields were obtained with catalytic amount of superacid ZrO_2:H_2SO_4.The calcinationtemperature greatly influenced the acid strength and activity of the superacid ZrO_2:H_2SO_4.Thesuperacid has both Lewis and Bronsted acid sites.The reversibility of Friedel-Crafts benzoylation andtransacylation were observed over the superacid.The used superacid could be readily regenerated andshowed identical benzoylation activity to toluene.     

Phase formation in mixed TiO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> oxides prepared by sol-gel method

Pure titania, zirconia, and mixed oxides (3–37 mol.% of ZrO₂) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the presence of 3–13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature increase above 700°C. The mixed oxide with 37 mol.% of ZrO₂ treated at 550°C shows a new single amorphous phase with a surface area of the nanoparticles double with respect to the other crystalline samples and the formed srilankite structure (at 700°C). The anatase phase is not observed in the sample containing 37 mol.% of ZrO₂. The treatment at 700°C causes the formation of the srilankite (Ti_0.63Zr_0.37O_x) phase.     

High-performance supercapacitors of hydrous ruthenium oxide/mesoporous carbon composites

The amorphous hydrous ruthenium oxide/mesoporous carbon composites (denoted as RuO₂·xH₂O/MC), obtained by loading small amount of amorphous hydrous ruthenium oxide nanoparticles ranged from 0.9 to 5.4% by weight of Ru (denoted as RuO₂·xH₂O) on mesoporous carbon (MC), were investigated for the first time and were used for supercapacitors. Electrochemical measurements showed that RuO₂·xH₂O/MC composites not only have an enhanced specific capacitance but also retain the superior rate capability of MC. The RuO₂·xH₂O/MC composite with Ru loading of 3.6 wt% exhibited an increase of the specific capacitance of approximately 57% (from 115 to 181 F/g) at the scan rate of 25 mV s⁻¹ in 0.1 M H₂SO₄ aqueous electrolyte. The specific capacitance based on the mass of RuO₂ was estimated to be 1,527 F/g, by subtracting the contribution from MC in the composite. Cycle performance tests for RuO₂·xH₂O/MC composite (3.6 wt% Ru) showed that approximately 2.8% loss of the total capacitance was observed after 1,000 cycles.     

Oxygen reduction behavior of RuO2/Ti,IrO2/Ti and IrM (M: Ru,Mo, W,V) Ox/Ti binary oxide electrodes in a sulfuric acid solution

Some oxide catalysts, such as RuO₂/Ti, IrO₂/Ti and IrM(M: Ru, Mo, W, V)O_x/Ti binary oxide electrodes, were prepared by using a dip-coating method on a Ti substrate. Their catalytic behavior for the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H₂SO₄ at 60 °C. These catalysts were found to exhibit considerably high activity, and the most active one among them was Ir_0.6V_0.4O₂/Ti prepared at 450 °C, showing onset potential for the ORR at about 0.86 V–0.90 (vs RHE).     

Preparation of Nanostructural ZrO2/SiO2 and Study on Catalytic Activity of its Superacid Catalyst

A novel material ZrO₂/SiO₂ was synthesized on SiO₂ support by means of electrostatic self‐assembly technique and sol‐gel method. After treating this material with 0.7 mol·L^?1 H₂SO₄, a nanostructural solid superacid catalyst SO₄^2?‐ZrO₂/SiO₂ was prepared. The material was characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Brunauer Emmett Teller method (BET) and Hammett indicator method. The catalytic activity of the catalyst was carried out for the esterification between acetic acid and butanol. Results show that the catalytic activity of this catalyst was much higher than that of powdered superacid catalyst SO₄^2?/ZrO₂. Due to the SiO₂ spherical support, the solid superacid catalyst could be separated and recovered easily. The nanostructural ZrO₂/SiO₂ will be a promising material for the chemical industry in the future.     

Application of RuO<Subscript>2</Subscript> Nanoparticles as Catalyst in Preparation of Indolo[3,2-a]Carbazoles

RuO₂ nanoparticles were readily prepared from RuCl₃·3H₂O via the formation of Ru-hydroxide precursor, followed by calcination at 550 °C. Under similar conditions, uniform dispersion of spherical RuO₂ nanoparticles over the surface of MCM-41 was also obtained. The synthesized materials were characterized by transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD), BET surface area measurements, and magnetic measurements (VSM). The obtained RuO₂ nanoparticles found application as catalyst in preparation of indolo[3,2-a]carbazoles from the reaction of indoles and benzils. Under mild reaction conditions, satisfactory yields of the desired products were obtained. Stabilization of RuO₂ nanoparticles over the surface of MCM-41 (RuO₂–MCM41), however, had the advantage of easy recycling, although a slight decrease in efficiency after five successive runs was observed.