Insights into SO2 Interaction with Pd/Co3O4–CeO2 Catalysts for Methane Oxidation

The catalytic performance and the sulphur resistance of a Pd (0.7 wt%) catalyst supported over Co₃O₄(30 wt%)–CeO₂(70 wt%) mixed oxide were investigated in the oxidation of methane under stoichiometric and lean conditions. The catalytic behaviour was compared with that of two reference catalysts, palladium supported over pure Co₃O₄ and CeO₂. Catalysts were characterized by XRD, BET, XPS and FTIR measurements. Regeneration by a CH₄-reducing treatment at 600 °C was investigated.     

SO4–ZrO2 catalysts for the esterification of benzoic acid to methylbenzoate

SO₄–ZrO₂ catalysts, prepared by varying the conditions of oxide preparation and H₂SO₄ impregnation, have been characterized by means of different techniques (XRD, BET, Hammett–Bertolacini technique, XPS). The esterification of benzoic acid to methylbenzoate has been used to test the different catalysts and their catalytic performance has been discussed in the light of their bulk and surface properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Behavior of alginate–gelatin blended gel with embedded macrovoids: Stress-induced changes and the solute release characteristics

Blending of gelatin to alginate promote cell–material interaction. However, the changes in diffusive and mechanical properties need to be ascertained. This study shows that the presence of two superposed polymer networks, where gelatin is not additionally crosslinked resulted in higher uptake and slower release of vitamin B₁₂. In the presence of gelatin, the stress is found higher for the same level of compressive deformation, and the permeability of the pore fluid during expulsion under compressive stress is found significantly lower. Also, a large residual strain at the end of each cycle in case of cyclic compression is observed, when gelatin is present. A microfluidic device is used to introduce voids uniformly across the blended gel with an objective to increase compressibility, permeability (for faster equilibration of pore pressure), and uptake of bioactive species. The results showing lower permeability and higher uptake in the presence of gelatin are discussed.     

Efficient structured catalysts for ethylene production through the ODE reaction: Ni and Ni–Ce on ceramic foams

Ni and Ni–Ce oxides alumina-supported formulations onto alpha-alumina foams were prepared, characterized and evaluated in the oxidative dehydrogenation of ethane (ODE) reaction. The catalysts were appropriately deposited on ceramic foams with a uniform, mechanically stable coverage. Besides, the structured systems were active and selective in the ODE reaction, demonstrating that the incorporation method was successful to obtain adequate active sites. Cerium markedly improved the ethane conversion due to a synergistic effect with nickel oxide, thus leading to a significant increment in ethylene productivity compared to that of the cerium-free system. An optimal Ce/Ni ratio was found which maximized the catalytic performance.     

Coke removal from deactivated Co–Ni steam reforming catalyst using different gasifying agents: An analysis of the gas–solid reaction kinetics

The reactivity of various gases, namely; O₂, air, CO₂, H₂ and N₂, with carbon deposited on alumina-supported Co–Ni catalyst during propane reforming in a fluidized bed reactor at 773–973 K using relatively low feed steam:carbon ratio (0.8–1.5) has been investigated in a thermogravimetric analysis unit. Analysis of the transient solid weight loss revealed that carbon removal mechanism is dependent on the type of gasifying agent. Carbon gasification kinetics using O₂ and air followed the Avrami-Erofeev (A2) model while data for both CO₂ and H₂ were captured by the geometrical (contracting area, R2) model. However, carbon gasification with inert N₂ proceeded at much slower rate (about 10 times lower than air) and was adequately fitted by the one-dimensional diffusion (D1) model. Specific reaction rates from these phenomenological models were also linearly correlated with the catalyst carbon content with reactivity coefficient of the gasifying agent decreasing in the order, O₂ > air > CO₂ > H₂ > N₂. In order to minimize energy consumption during catalyst regeneration, reduce greenhouse gas emissions and reduce catalyst sintering, it would be desirable to employ a mixture of air and CO₂ as the carbon gasifying agent to take advantage of the coupled exothermic (air oxidation) and endothermic (reverse Boudouard reaction involving CO₂ and carbon) nature taking place during the carbon removal operation.     

Effect of different iron precursors on the synthesis and photocatalytic activity of Fe–TiO2 nanotubes under visible light

Fe–TiO₂ nanotubes (Fe-TNTs) were developed to entitled photocatalytic reactions using a visible range of the solar spectrum. This work reports on the effect of different Fe precursors on the synthesis, characterization, kinetic study, material and photocatalytic properties of Fe-TNTs prepared by electrochemical method using three different Fe precursors i.e. (iron nitrate [Fe(NO₃)₃⋅9H₂O], iron sulfate [FeSO₄⋅7H₂O], and potassium iron ferricyanide [K₃Fe(CN)₆]). X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy are used to examine the influence of the Fe precursor on the Fe-TNTs material characterization. Different Fe-TNT properties, such as enhanced photoactivity, good crystallization, and composition of titania structures (anatase and rutile) could be acquired from different iron precursors. Among the three iron precursors, Fe(NO₃)₃ provided with the only anatase phase, yields the highest photocatalytic activity. Congo red is used as a model compound to check the photocatalytic efficiency of synthesized materials because it has a complex aromatic structure which makes it difficult to be biodegraded or oxidized with the aid of chemicals. The photocatalytic efficiency of all Fe-TNT can be arranged in the following order: TNT-FeN > TNT-FeS > TNT-FeK > TNT. The kinetic rate constant of congo red degradation using the Fe-TNT with Fe(NO₃)₃ was 0.44 h⁻¹ with a half-life of 1.57 h⁻¹     

Preparation of solid acid catalyst SO42−/TiO2/γ-Al2O3 for esterification: A study on catalytic reaction mechanism and kinetics

In this work, a series of SO₄^2-/TiO₂/γ-Al₂O₃ solid acid catalysts were synthesized by impregnation method, in which nano-TiO₂ was prepared by sol-gel method, and then the nano-TiO₂ sol was loaded on porous γ-Al₂O₃ supporter through impregnation. The structure and property of catalyst were characterized by XRD, N₂-BET, SEM, TEM, XPS, NH₃-TPD, Pyridine-IR and FT-IR. In addition, the catalyst of chelate bidentate coordination acid center model was established. The catalytic performance test was carried out in the esterification of n-butyl alcohol with lauric acid and the catalyst showed excellent activity. The experimental results showed that the medium strength acid sites were more dominant active sites than the strong and weak acid sites for the rapid esterification reaction. Its kinetic behaviors and activation energy were studied for the esterification under the catalytic reaction condition.     

A novel solid–liquid route for the preparation of Cu3Se2 and Ag2Se nanocrystals

Cu₃Se₂ and Ag₂Se nanocrystals have been synthesized with Se as the precursor in aqueous solutions under photo-irradiation at room temperature. The obtained products were analyzed through X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results showed that the tetragonal phase of Cu₃Se₂ with nearly spherical grains and the orthorhombic phase of Ag₂Se with nanoscale dendrite were formed. The experiments also confirmed that photo-irradiation and Na₂SO₃ played important roles in the formation of Cu₃Se₂ and Ag₂Se nanocrystals. The formation mechanism of Cu₃Se₂ and Ag₂Se nanocrystals was investigated in detail.     

Effect of the Ag–CeO2 interaction and the nature of pore structure on the catalytic activities of different Ag–CeO2/mesoporous-SiO2 catalysts on the reduction of 4-nitrophenol

Journal of Porous Materials - Photocatalytic reduction of 4-nitrophenol is one of the important waste-utilization techniques that transform toxic para-nitrophenol to useful chemicals, such as...     

Comparison of different alumina powders for the aqueous processing and pressureless sintering of Al2O3–SiC nanocomposites

Four different alumina powders, from European and Japanese sources having similar particle size (350–700 nm) were used for the fabrication of nanocomposites. They were compared in terms of green properties, sintering behaviour, microstructure and mechanical properties. The processing route used (attrition milling and freeze-drying) leads to a reduction in green density of the processed aluminas and composites compared to the as-received alumina. All powders had similar green properties except one, which contained a binder from the manufacturer. The presence of this binder led to the formation of hard agglomerates. In this case the pressing did not eliminate, totally, the inter-agglomerate pores, leading to an incomplete sintering. Calcining the powder to remove the binder resulted in similar pressing and sintering behaviour to the other powders and densities >99% were achieved at 1750 °C by pressureless sintering. All the composites exhibited similar microstructures (matrix grain size ∼3 μm) and elastic properties, hardness and fracture toughness. A finer matrix microstructure could be obtained with one of the European powders which achieved ∼99% density at 1700 °C. The presence of 5 vol.% SiC resulted in a mean grain size of ∼2 μm for the alumina matrix compared with 13.9 μm for a monolithic alumina prepared under identical conditions.     

Preparation and evaluation of RuO2–IrO2, IrO2–Pt and IrO2–Ta2O5 catalysts for the oxygen evolution reaction in an SPE electrolyzer

IrO₂–RuO₂, IrO₂–Pt and IrO₂–Ta₂O₅ electrocatalysts were synthesized and characterized for the oxygen evolution in a Solid Polymer Electrolyte (SPE) electrolyzer. These mixtures were characterized by XRD and SEM. The anode catalyst powders were sprayed onto Nafion 117 membrane (catalyst coated membrane, CCM), using Pt catalyst at the cathode. The CCM procedure was extended to different in-house prepared catalyst formulations to evaluate if such a method could be applied to electrolyzers containing durable titanium backings. The catalyst loading at the anode was about 6 mg cm⁻², whereas 1 mg cm⁻² Pt was used at the cathode. The electrochemical activity for water electrolysis was investigated in a single cell SPE electrolyzer at 80 °C. It was found that the terminal voltage obtained with Ir–Ta oxide was slightly lower than that obtained with IrO₂–Pt and IrO₂–RuO₂ at low current density (lower than 0.15 A cm⁻²). At higher current density, the IrO₂–Pt and IrO₂–RuO₂ catalysts performed better than Ir–Ta oxide.     

Influence of Mn and Fe Addition on the NO x Storage–Reduction Properties and SO2 Poisoning of a Pt/Ba/Al2O3 Model Catalyst

This work deals with the effect of Mn or Fe addition on the NO _x storage–reduction properties of a Pt/Ba/Al₂O₃ model catalyst. NO _x storage capacity, SO₂ poisoning and regeneration and NO _x removal efficiency under rich/lean cycling conditions are studied. Fe addition to Pt/Ba/Al₂O₃ leads only to a small increase of NO _x storage capacity, and more interestingly, to a better sulfur removal due to the inhibition of bulk barium sulfate formation. Unfortunately, the NO _x storage property cannot be fully recovered. Moreover, Fe addition results in a decrease in the NO _x removal efficiency. Mn addition also improves the NO _x storage capacity, but no significant influence on the sulfur elimination is observed. Mn-doped catalyst does not improve the NO _x removal efficiency, but NH₃ selectivity is found to drastically decrease at 400 °C, from 20 to 3%. In addition, the NO _x conversion can be improved at higher H₂ concentration in the rich pulse, always keeping NH₃ selectivity at low level.     

Influence of iron content on the color of the C3A–Fe2O3 system synthesized under different conditions of temperature,atmosphere and cooling

The 3CaO·Al₂O₃–Fe₂O₃ (C₃A–Fe₂O₃) system is important for the production of white clinker. In the present study this system was examined from the perspective of improving the sustainability of the production process. Microstructural evaluation was employed to explain the changes in color caused by variation of: iron content; temperature; type of atmosphere; and cooling conditions. It was found that color was more significantly affected by the iron content, temperature and type of atmosphere than by the type of cooling used. It was also observed that the utility of iron-rich raw materials could be maximized by understanding and enhancing the solubility of Fe₂O₃ in C₃A. It was found that a 2 wt.% Fe₂O₃ solid solution was stable only under kiln open to atmospheric conditions and remained clear at temperatures up to 1370 °C. However, the same 2 wt.% Fe₂O₃ solid solution suffered a significant change in color when the temperature rose to 1400 °C. Mössbauer spectroscopy showed that the oxidation state of Fe was Fe³⁺, which did not change between 1370 and 1400 °C; however, a structural change in the C₃A–Fe₂O₃ solid solution was detected as a result of the alteration of the thermal treatment. The distinction between the structures at these two temperatures was that at 1370 °C, all of the Fe³⁺ had a tetrahedral coordination, while at 1400 °C, 19 wt.% of the Fe³⁺ appeared in octahedral sites, a result that was corroborated by Rietveld analysis.     

Corrosion of SiO2–B2O3–Al2O3–CaF2-R2O (R=Na and K) enamels with different content of ZrO2 in H2SO4 and NaOH solutions

Corrosion of three SiO₂–B₂O₃–Al₂O₃–CaF₂-R₂O (R = Na and K) based enamels with different ZrO₂ contents in H₂SO₄ and NaOH solutions was studied. The addition of ZrO₂ reduced acid resistance of enamels. Especially for enamel with 5 wt% zirconia, the weight loss reached 4.04 mg/cm² after 30-day corrosion. On the contrary, substituting ZrO₂ for SiO₂ greatly improved the alkali resistance of enamel, since the weight loss of enamel with ZrO₂ was only 0.3 mg/cm² after 20-h corrosion, which decreased to less than one third of that of enamel without ZrO₂. Corrosion mechanism was comparatively discussed in these two solutions.     

Cu2O/nano-CuFe2O4: A novel and recyclable magnetic catalyst for three-component coupling of carbonyl compounds–alkynes–amines under solvent-free condition

Cu₂O/nano-CuFe₂O₄ magnetic composite with different loadings of Cu₂O has been synthesized by feasible and low-cost method. The as-prepared composite was fully characterized by FT-IR, XRD, FEG-SEM, EDS and VSM analyzer. The catalytic activity of magnetic composite for synthesis of propargylamines was evaluated. The catalyst has many obvious advantages and easily separated via an external magnet. It can be reused for five successive runs.