Parametric study of coiled carbon fibre synthesis on an in situ generated H2S-modified Ni/Al2O3 catalyst

Coiled carbon fibre (CCF) synthesis on an in situ generated H₂S-modified Ni/Al₂O₃ catalyst is investigated using a high-throughput reaction system that allows real time observation of weight changes. The influence of reduction and synthesis temperatures, reduction duration, H₂ addition during synthesis, synthesis duration, C₂H₂ concentration in the synthesis gas and catalyst loading are investigated and products are analysed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. Thermodynamic equilibrium models of various experimental scenarios provide insight into the predominant species present at equilibrium. Reduction temperature and reduction duration affect H₂S concentration, a vital parameter for CCF synthesis, and CCFs form in only a narrow reduction and synthesis temperature range of 650 °C ± 50 °C with greatest coil yields observed at 650 °C and following reduction durations of between 1 and 20 min with greatest coil yields observed after a 10 min reduction. The presence of H₂ during synthesis was found to have a positive effect on CCF formation. The ratio of thick to thin carbon fibres increased with catalyst nickel loading and the greatest ratio of CCFs was produced with a 1:20 wt. Ni:Al₂O₃ catalyst.     

Ni/Al_2O_3催化剂的CO_2-TPD表征

Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。     

Modelling of citral hydrogenation kinetics on an Ni/Al2O3 catalyst

The kinetics of citral hydrogenation in ethanol over an Ni/Al₂O₃ catalyst was studied in a slurry reactor operating at atmospheric pressure and at a temperature range of 60–77°C. Citronellal was the primary reaction product, whereas the amounts of unsaturated alcohols were very minor. Citronellol was the dominating product, generated mainly through the hydrogenation of the carbonyl group of citronellal. Based on the experimental data, a kinetic model was developed for hydrogenation. The model comprises competitive and rapid adsorption steps as well as rate-determining hydrogenation steps. The mass transfer limitation of hydrogen was included in the mathematical model. The kinetic parameters and the mass transfer parameter of hydrogen were estimated from the experimental data. A comparison of the model predictions with the experimental data revealed that the proposed kinetic approach gave a satisfactory reproduction of the data.     

Ethylene dimerization over NiSO4 supported on Fe2O3-promoted ZrO2 catalyst

The NiSO₄ supported on Fe₂O₃-promoted ZrO₂ catalysts were prepared by the impregnation method. Fe₂O₃-promoted ZrO₂ was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe₂O₃–ZrO₂. The addition of nickel sulfate (or Fe₂O₃) to ZrO₂ shifted the phase transition of ZrO₂ (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Fe₂O₃) and ZrO₂. 15-NiSO₄/5-Fe₂O₃–ZrO₂ containing 15 wt.% NiSO₄ and 5 mol% Fe₂O₃, and calcined at 500 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO₄/Fe₂O₃–ZrO₂ catalysts was very effective for ethylene dimerization even at room temperature, but Fe₂O₃–ZrO₂ without NiSO₄ did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe₂O₃ up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Fe₂O₃ and ZrO₂ and due to consequent formation of Fe–O–Zr bond.     

Effective kinetics of 3-hydroxypropanal hydrogenation over Ni/SiO2/Al2O3 catalyst

Concentration-time curves at 45-80°C and 2.60-5.15 MPa were measured, in a spinning basket reactor, to model the hydrogenation of 3-hydroxypropanal (HPA) to 1,3-Propanediol (PD) over Ni/SiO₂/Al₂O₃ catalyst pellets. A mathematical model whose parameters are effective diffusion coefficients and intrinsic kinetic parameters is proposed to describe this process and to avoid the dependence of the model parameters on the catalyst particle size. This model fits the experimental data reasonably and allows a reliable scale up of this process in comparison to other empirical models.     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.     

Investigation of the solidification behavior of Al2O3/YAG/YSZ ceramic in situ composite with off-eutectic composition

Directionally solidified Al₂O₃/YAG/YSZ ceramic in situ composite is an interesting candidate for the manufacture of turbine blade because of its excellent mechanical property. In the present study, two directionally solidified hypoeutectic and hypereutectic Al₂O₃/YAG/YSZ ceramic in situ composites are prepared by laser zone remelting, aiming to investigate the solidification behavior of the ternary composite with off-eutectic composition under high-temperature gradient. The results show that the composition and laser scanning rate significantly influence the solidification microstructure. The ternary in situ composite presents ultra-fine microstructure, and the eutectic interspacing is refined with the increase of the scanning rate. The Al₂O₃/YAG/YSZ hypoeutectic ceramic displays an irregular hypoeutectic network structure consisting of a primary Al₂O₃/YAG binary eutectic and fine Al₂O₃/YAG/YSZ ternary eutectic. Only at low scanning rate, homogeneous ternary eutectic-like microstructures are obtained in the hypoeutectic composition. Meanwhile, the Al₂O₃/YAG/YSZ hypereutectic ceramic shows homogeneous eutectic-like microstructure in most cases and the eutectic interspacing is finer than the ternary eutectic. Furthermore, the formation and evolution mechanism of the off-eutectic microstructure of the ternary composite are discussed.     

In situ TEM observation of crack propagation in LiTaO3 particle toughened Al2O3 ceramics

Direct observation of crack propagation in LiTaO₃/Al₂O₃ composite ceramics was carried out using in situ transmission electron microscopy (TEM). Domain switching induced by crack propagation, crack deflection and branching at domain boundaries and ripples similar to the contrasts of 180° domains at the microcrack tip inside LiTaO₃ grains were detected evidently. Domain switching, crack deflection, branching and energy dissipation resulting from the formation of contrasts similar to the 180° domains at the microcrack tip, were proposed as the toughening mechanisms in LiTaO₃/Al₂O₃ ceramics.     

Microstructure, growth mechanism and mechanical property of Al2O3-based eutectic ceramic in situ composites

Directionally solidified Al₂O₃-based eutectic ceramic in situ composites with inherently high melting point, low density, excellent microstructure stability, outstanding resistance to creep, corrosion and oxidation at elevated temperature, have attracted significant interest as promising candidate for high-temperature application. This paper reviews the recent research progress on Al₂O₃-based eutectic ceramic in situ composites in State Key Laboratory of Solidification Processing. Al₂O₃/YAG binary eutectic and Al₂O₃/YAG/ZrO₂ ternary eutectic ceramics are prepared by laser zone melting, electron beam floating zone melting and laser direct forming, respectively. The processing control, solidification characteristic, microstructure evolution, eutectic growth mechanism, phase interface structure, mechanical property and toughening mechanism are investigated. The high thermal gradient and cooling rate during solidification lead to the refined microstructure with minimum eutectic spacing of 100 nm. Besides the typical faceted/faceted eutectic growth manner, the faceted to non-faceted growth transition is found. The room-temperature hardness H_V and fracture toughness K_IC are measured with micro-indentation method. For Al₂O₃/YAG/ZrO₂, K_IC = 8.0 ± 2.0 MPa m^1/2 while for Al₂O₃/YAG, K_IC = 3.6 ± 0.4 MPa m^1/2. It is expectable that directionally solidified Al₂O₃-based eutectic ceramics are approaching practical application with the advancement of processing theory, technique and apparatus.     

Ru-Fe/Al_2O_3氧化-还原性能探究

以Al_2O_3为载体,RuCl_3·xH_2O和FeCl_3·6H_2O为活性组分前驱体,采用吸附-沉淀法制备了Ru-Fe/Al_2O_3和Ru/Al_2O_3催化剂,以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应,结合H_2-TPR和XRD表征技术,考察Fe改性Ru基催化剂的氧化-还原性能及催化活性。经氧化-还原循环处理后,催化剂Ru-Fe/Al_2O_3上马来酸二甲酯加氢活性高于Ru/Al_2O_3。XRD结果显示,经处理的Ru-Fe/Al_2O_3上未见金属Ru的特征衍射峰,而Ru/Al_2O_3上出现了金属Ru的特征衍射峰。结合H_2-TPR结果推断,Ru与Fe之间发生了相互作用,这种协同作用可以改善Ru/Al_2O_3催化剂的热稳定性。     

Characterizations and activities of the nano-sized Ni/Al2O3 and Ni/La–Al2O3 catalysts for NH3 decomposition

A series of nano-sized Ni/Al₂O₃ and Ni/La–Al₂O₃ catalysts that possess high activities for NH₃ decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N₂ adsorption/desorption, XRD, H₂-TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni⁰ particles with the average size lower than 5.0 nm are always obtained even though the Ni loading ranged widely from 4 to 63%. Compared with the Ni/Al₂O₃ catalysts, the Ni/La–Al₂O₃ ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni–Al mixed oxide phase was detailed.     

Lean NOx reduction with CO + H2 mixtures over Pt/Al2O3 and Pd/Al2O3 catalysts

The reduction of NO_x by hydrogen under lean burn conditions over Pt/Al₂O₃ is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO_x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al₂O₃. In this case, although pure H₂ and pure CO are ineffective for NO_x reduction under lean burn conditions, H₂/CO mixtures are very effective. With a realistic (1:3) H₂:CO ratio, typical of actual exhaust gas, Pd/Al₂O₃ is significantly more active than Pt/Al₂O₃, delivering 45% NO_x conversion at 160 °C, compared to >15% for Pt/Al₂O₃ under identical conditions. The nature of the support is also critically important, with Pd/Al₂O₃ being much more active than Pd/SiO₂. Possible mechanisms for the improved performance of Pd/Al₂O₃ in the presence of H₂+CO are discussed.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Mixtures of carbon and Ni/Al2O3 as catalysts for the microwave-assisted CO2 reforming of CH4

In this work, the microwave-assisted CO₂ reforming of CH₄ over mixtures of carbonaceous materials and an in-lab prepared Ni/Al₂O₃ was studied. Ni/Al₂O₃ is not heated by microwave radiation, and for this reason, microwave receptors, such as carbonaceous materials, must be mixed with this catalyst. In order to evaluate the role of the carbonaceous component of the blend, two different carbonaceous materials were used: an activated carbon, FY5, and a metallurgical coke, CQ. The carbonaceous component acted not only as microwave receptor but also as catalyst and, consequently, it influenced the catalytic activity of the mixture. FY5 + Ni/Al₂O₃ was found to be a better catalyst than CQ + Ni/Al₂O₃, since FY5 on its own showed a better catalytic activity than CQ. Ni/FY5, which consists of Ni impregnated directly onto the microwave receptor, was also evaluated as a catalyst. It was found that the catalytic activity of the mixture FY5 + Ni/Al₂O₃ was better than that of Ni/FY5. Finally, the influence of the heating device on the catalytic activity of FY5 + Ni/Al₂O₃ was studied. Conversions over FY5 + Ni/Al₂O₃ and microwave heating were found to be similar to conversions over Ni/Al₂O₃ and conventional heating.     

Structure and reactivity of plasma treated Ni/Al2O3 catalyst for CO2 reforming of methane

The glow discharge plasma treated Ni/Al₂O₃ catalyst showed an excellent anti-coke property for CO₂ reforming of methane. Characterizations using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), transmission electron microscopy (TEM), and CO adsorbed infrared spectroscopy (IR) were conducted to investigate the structure and reactivity of the plasma treated Ni/Al₂O₃ catalyst for CO₂ reforming of methane. It confirms that the plasma treatment of Ni precursor at room temperature followed by calcination thermally has a significant influence on the surface characteristics of the active phase. The plasma treated catalyst contains high concentration of close packed plane with improved Ni dispersion and enhanced Ni-alumina interaction, which lead to high catalytic activity and excellent resistance to formations of filamentous carbon and encapsulating carbon.     

In situ synthesis of Au/Ti-HMS and its catalytic performance in oxidation of bulky sulfur compounds using in situ generated H2O2 in the presence of H2/O2

Gold particles are supported on Ti-containing mesoporous silica (Ti-HMS) through an in situ process. The obtained samples were characterized by a series of techniques including ICP, powder X-ray diffraction, N₂ sorption, UV-visible spectroscopy and transmission electron microscopy. The performance of the catalyst in direct synthesis of H₂O₂ from H₂/O₂ in methanol solvent and oxidative desulphurization using the in situ generated H₂O₂ have been systematically investigated. The results show that in situ synthesized Au/Ti-HMS, the organic template of which is eliminated via extraction with ethanol, successfully maintains the typical wormhole structure of HMS and possesses uniform mesopores, which is confirmed by N₂ sorption and TEM. UV-visible spectroscopy result confirms the simultaneous existence of Au and Ti active centers in this bifunctional catalyst. Gold particles supported on Ti-HMS show high activity in the direct synthesis of H₂O₂ from H₂ and O₂ in methanol solvent. Furthermore, high removal rate of bulky sulfur compounds can be obtained using the in situ generated H₂O₂ over Au/Ti-HMS. Final conversion rate of the substrates confirms the dominant role of the in situ H₂O₂ oxidation in deep desulphurization. In addition, this bifunctional catalyst can avoid the insufficiency of H₂O₂ caused by the decomposition comparing with the Ti-HMS/commercial H₂O₂ system.     

Catalytic oxidation of naphthalene using a Pt/Al2O3 catalyst

Polycylic aromatic hydrocarbons (PAHs) are listed as carcinogenic and mutagenic priority pollutants, belonging to the environmental endocrine disrupters. Most PAHs in the environment stem from the atmospheric deposition and diesel emission. Consequently, the elimination of PAHs in the off-gases is one of the priority and emerging challenges. Catalytic oxidation has been widely used in the destruction of organic compounds due to its high efficiency (or conversion of reactants), its economic benefits and good applicability.

This study investigates the application of the catalytic oxidation using Pt/γ-Al₂O₃ catalysts to decompose PAHs and taking naphthalene (the simplest and least toxic PAH) as a target compound. It studies the relationships between conversion, operating parameters and relevant factors such as treatment temperatures, catalyst sizes and space velocities. Also, a related reaction kinetic expression is proposed to provide a simplified expression of the relevant kinetic parameters.

The results indicate that the Pt/γ-Al₂O₃ catalyst used accelerates the reaction rate of the decomposition of naphthalene and decreases the reaction temperature. A high conversion (over 95%) can be achieved at a moderate reaction temperature of 480 K and space velocity below 35,000 h⁻¹. Non-catalytic (thermal) oxidation achieves the same conversion at a temperature beyond 1000 K. The results also indicate that Rideal–Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-first-order reaction kinetic equation with activation energy of 149.97 kJ/mol and frequency factor equal to 3.26 × 10¹⁷ s⁻¹.     

Direct synthesis of H2O2 acid solutions on carbon cathode prepared from activated carbon and vapor-growing-carbon-fiber by a H2/O2 fuel cell

Direct synthesis of H₂O₂ acid solutions was studied using a gas-diffusion cathode prepared from activated carbon (AC), vapor-growing-carbon-fiber (VGCF) and poly-tetra-fluoro-ethylene (PTFE) powders, with a new H₂/O₂ fuel cell reactor. O₂ reduction to H₂O₂ was remarkably enhanced at the three-phase boundary (O₂(g)-electrode(s)-acid(l)) at the [AC + VGCF] cathode. Fast diffusion processes of O₂ to the active surface and of H₂O₂ to the bulk acid solutions were essential for H₂O₂ accumulation. Synergy of AC and VGCF was observed for the H₂O₂ formation. RRDE and cyclic voltammetry studies indicated that the surface of AC functioned as the active phase for O₂ reduction to HO₂, and VGCF functioned as an electron conductor and a promoter to convert HO₂ to H₂O₂. A maximum H₂O₂ concentration of 353 mM (1.2 wt%) was accomplished under short-circuit conditions (current density 12.7 mA cm⁻², current efficiency 40.1%, geometric area of cathode 1.3 cm², reaction time 6 h).