Effect of Fe2O3 on properties and densification of Ce0.8Gd0.2O2−δ by PCAS

Dense Ce_0.8Gd_0.2O_2−δ was sintered by pulsed current activated sintering (PCAS) within 6 min from Ce_0.8Gd_0.2O_2−δ nanopowder prepared by co-precipitation method. Sintering was accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense Ce_0.8Gd_0.2O_2−δ with relative density of up to 96.3% was produced under simultaneous application of an 80-MPa pressure and the pulsed current. The effects of Fe₂O₃ additions on the sintering behavior, ionic conductivities, and mechanical properties of the Ce_0.8Gd_0.2O_2−δ were investigated.     

Effect of calcination temperature on the oxidation of benzene with ozone at low temperature over mesoporous α-Mn2O3

Highly ordered mesoporous α-Mn₂O₃ was synthesized from cubic mesoporous silica (KIT-6) via nano-casting method. The mesoporous α-Mn₂O₃ thus obtained was calcined at 200-500 °C, and characterized using XRD, N₂ sorption and temperature-programmed reduction (TPR). The calcination temperature did not significantly affect the BET surface areas, mesopore sizes, pore structures and crystallinities of the mesoporous α-Mn₂O₃ materials. The mesoporous α-Mn₂O₃ calcined at 300 °C showed the highest catalytic activity due to its high reduction ability revealed from the TPR analysis. However, the catalytic activity was negligible without ozone. In addition, the selectivity to CO₂ was about 90% and this seems to be an advantage of mesoporous α-Mn₂O₃ for removing benzene using ozone.     

Non-thermal plasma assisted CO2 reforming of propane over Ni/γ-Al2O3 catalyst

Non-thermal plasma (NTP) assisted CO₂ reforming of propane was studied in combination with a Ni/γ-Al₂O₃ catalyst. The activation temperature of the catalyst is reduced, and the conversion of the reactants is improved compared with the summed results of the plasma and catalytic modes. The selectivity of H₂ and CO is greatly enhanced. Both excited species produced by NTP and the interaction of NTP with the catalyst are probably responsible for the decrease of the activation temperature of the catalyst. Synergistic effect between the plasma and the catalyst leads to the improvement of the conversion of reactants and the selectivity of H₂ and CO.     

Spinelisation and properties of Al2O3–MgAl2O4–C refractory: Effect of MgO and Al2O3 reactants

The effect of particle size of MgO and Al₂O₃ on the spinel formation associated with permanent linear change on reheating (PLCR) and microstructure of Al₂O₃–MgAl₂O₄–C refractory is investigated as a function of heating cycle at 1600 °C with 2 h holding at each cycle. It was found that rate of spinel formation and associated volume expansion is very much dependent on the reactivity and particle size of the reactant. When the reactants are very fine and reactive there is considerable amount of spinel formation, whereas coarser reactants with lower reactivity show negligible formation of spinel phase and associated expansion. Magnesia and alumina with moderate reactivity develops optimum PLCR of the refractory. It continuously increases with the number of heating cycles. The SEM photomicrographs show that in Al₂O₃–MgAl₂O₄–C refractory the spinel phase is formed in between the calcined bauxite grain and the EDX analysis indicates that the spinel phase formed is stoichiometric in nature.     

Dehydrogenation of propane in the presence of N2O over In2O3―Al2O3 mixed oxide catalysts

Dehydrogenation of propane coupled with N₂O over a series of binary In₂O₃―Al₂O₃ mixed oxides was investigated. In contrast to the poor performance for sole N₂O decomposition, a remarkable synergy was identified between N₂O decomposition and propane dehydrogenation. Among the catalysts tested, the In₂O₃―Al₂O₃ sample containing a 20 mol% In₂O₃ showed the highest activity for propane dehydrogenation in the presence of N₂O. Moreover, stability far superior to those of the conventional iron-based materials was observed, attributable to the moderate surface acidity of the In―Al―O composite. The essential role of N₂O is suggested to generate active oxygen species facilitating propane dehydrogenation.     

Coke deposition mechanism on the pores of a commercial Pt-Re/γ-Al2O3 naphtha reforming catalyst

Coke deposition mechanism on a commercial Pt-Re/γ-Al₂O₃ naphtha reforming catalyst was studied. A used catalyst that was in industrial reforming operation for 28 months, as well as the fresh catalyst of the unit were characterized using XRD, XRF, and nitrogen adsorption/desorption analyses. Carbon and sulfur contents of the fresh and the used catalysts were determined using Leco combustion analyzer. The pore size distributions (PSD) of the fresh and the used reforming catalysts were determined using BJH and Comparison Plot methods. The Comparison Plot method produced the most reasonable PSDs for the catalysts. Through comparison of the PSDs of the fresh and the used catalysts, it was revealed that coke deposited on both micropores and mesopores of the catalyst at a constant thickness of 1.0 nm. The constant coke thickness on the catalyst pore walls in the naphtha reforming process (temp. ∼ 500 °C) implies that coke deposition reaction is the slow controlling step in comparison to the fast mass transfer rate of coke ingredients into the pores. The bulk density of the deposited coke on the used catalyst was calculated as 0.966 g/cm³.     

Intrinsic kinetics for the synthesis of acetonitrile from ethanol and ammonia over Co–Ni/γ–Al2O3 catalyst

The intrinsic kinetics was studied for the synthesis of acetonitrile from amination–dehydrogenation of ethanol over the Co–Ni/γ–Al₂O₃ catalyst in the fixed-bed reactor. Experiments were carried out at reaction temperatures in the range 613–643 K, reactor pressure of 0.1 MPa, the ratios of volume feed velocity to catalyst volume (V₀/V_R) more than 12.99 min⁻¹ and large excesses of ammonia concentration over that of ethanol. The power-law model was used to fit the experimental data, and the model parameters were estimated using the Matlab software. Finally, a reaction kinetic model was proposed to describe the reaction, the calculated activation energy was 51.18 kJ mol⁻¹ and the reaction order to ethanol was 1.183.     

Effect of Bi2O3 on the electrochemical performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The LaBaCo₂O_5+δ−x wt.% Bi₂O₃ (LBCO-xBi₂O₃, x=10, 20, 30, and 40) were prepared as composite cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) via the conventional mechanical mixing method. The effect of Bi₂O₃ on polarization resistance, overpotential, and long-term stability of the LBCO cathode was investigated. An effective sintering aid for LBCO cathode, Bi₂O₃ not only lowers its sintering temperature by ~200 °C, but also improves the electrochemical performance within the intermediate temperature range of 600–800 °C. Electrochemical impedance spectroscopy measurements showed that the addition of 20 wt% Bi₂O₃ to LBCO exhibited the lowest area-specific resistance of 0.020 Ω cm² at 800 °C in air, which was about a seventh of that of the LBCO cathode at the same condition. At a current density of 0.2 A cm⁻², the cathodic overpotential of LBCO-20Bi₂O₃ was about 12.6 mV at 700 °C, while the corresponding value for LBCO was 51.0 mV. Compared to B₂O₃–Bi₂O₃–PbO frit, the addition of Bi₂O₃ significantly improved the long-term stability of cathode. Therefore, LBCO-20Bi₂O₃ can be a promising cathode for IT-SOFCs.     

Effect of the addition ZrO2–Al2O3 on nanocrystalline hydroxyapatite bending strength and fracture toughness

Nanocrystalline hydroxyapatite powder has been synthesized from a Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ solution by the precipitation method. In the next step we prepared ZrO₂–Al₂O₃ powder. After preparation, the powder was dried at 80 °C and calcined at 1200 °C for 1 h. Various amounts (HAP–15 wt% ZA, HAP–30 wt% ZA) of powder were mixed with the hydroxyapatite by ball milling. The powder mixtures were pressed and sintered at 1000 °C, 1100 °C and 1200 °C for 1 h. In order to study the structural evolution, X-ray diffraction (XRD) was used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to estimate the particle size of the powder and observe fracture surfaces. Results show that the bending strength of pressed nanocrystalline HAP was improved significantly by the addition 15 wt% of ZrO₂–Al₂O₃ powders at 1200 °C, but the fracture toughness was not changed, however when 30 wt% of ZA powders were added to nanocrystalline HAP, the bending strength and fracture toughness of the specimens decreased at all sintering temperature.     

The adsorption characteristics of two Mo sites on a sulfided MoO3/γ-Al2O3 surface

The surface structure of the oxidized and ammonia dissolved MoO₃/-Al₂O₃ samples and the adsorption characteristics of the sulfided samples were investigated by Laser Raman Spectroscopy (LRS) and Low Temperature Infrared Spectroscopy (LTIR) techniques.It was verified that there were two kinds of coordinated unsaturated Mo sites (denoted as Mo_A(CUS) and Mo_B(CUS)) on the surface and the precursors of Mo_A(CUS) and Mo_B(CUS) were Mo(O) and Mo(T), respectively. It was also concluded that Mo_A(CUS) sites could adsorb NO and CO, while Mo_B(CUS) could adsorb CO only. The surface concentration of Mo_A(CUS) might be far smaller than that of Mo_B(CUS).     

Catalytic removal of NO in waste incineration processes over Rh/Al2O3 and Rh–Na/Al2O3: Effects of particulates,heavy metals,SO2 and HCl

Two novel catalysts Rh/Al₂O₃ and Rh–Na/Al₂O₃ were prepared for NO removal and tested their practical performances in a laboratory-scale waste incineration system. The effects of particulates, heavy metals, and acid gases on the catalysts were evaluated and investigated through several characterization techniques, such as SEM, EA, XRPD, ESCA, and FTIR. The results indicated that the NO conversions were increased with the accumulation of particulates on the surface of catalysts, which was attributed to the increase in carbon content. However, the increase in heavy metals Cd and Pb contents on the surface of catalysts decreased the activity of catalyst for NO removal but did not change the chemical state of Rh and Na. The Rh/Al₂O₃ catalysts were poisoned when the acid gases SO₂ and HCl were present in the flue gas, because Rh and Al reacted with S and Cl to form inactive products. Adding Na to Rh/Al₂O₃ catalysts produced a promoting effect for SO₂ removal due to the formation of Na₂SO₄. The influence levels of different pollutants on the performances of Rh/Al₂O₃ and Rh–Na/Al₂O₃ catalysts for NO removal followed the sequence of HCl > heavy metals > SO₂ > particles.     

Effect of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo: II. Electrodeposition in the presence of SiC and Al2O3 and production of ZnCo–SiC and ZnCo–Al2O3 coatings

SiC or Al₂O₃ microsized particles were added to acid sulfate-based solutions for the electrodeposition of Zn, Co, and ZnCo. Initially, their effects on the electrochemical processes were evaluated. The Zn electrodeposition rate was increased in both SiC and Al₂O₃-loaded solutions. The Co electrodeposition rate was also increased by SiC. However, Al₂O₃ decreased it, especially at the beginning. Both SiC and Al₂O₃ influenced the electrodeposition of ZnCo positively at moderate loadings. The factors involved in producing ZnCo–SiC and ZnCo–Al₂O₃ composites were evaluated. ZnCo–SiC composites could be deposited with a higher [Co/Zn] ratio in the metal matrix than for pure ZnCo. In ZnCo–Al₂O₃, the [Co/Zn] ratio was smaller than in ZnCo and ZnCo–SiC. It was necessary to reduce the CoSO₄ concentration to improve the Al₂O₃ co-deposition. The variation in [Co/Zn] ratio could, in principle, be related to the effects of SiC and Al₂O₃ on the individual Zn and Co electrodeposition.     

Effect of the Nb2O5 content on electrical properties of lead-free BaTiO3–Bi0.5Na0.5TiO3 ceramics

(1−x)BaTiO₃–xBi_0.5Na_0.5TiO₃ (BT–BNT) ceramics were prepared by the solid-state reaction method. With an increase of BNT content, both the Curie temperature and the room temperature resistivity increased. At 1 mol% BNT addition, the sample was not semiconducting, due to Bi₂O₃ volatilization resulting from the decomposition of pre-calcined BNT during sintering. Appropriate extra Nb₂O₅ doping in the raw materials could offset Bi₂O₃ volatilization and neutralize the redundant acceptor Na⁺ ions. When the extra Nb₂O₅ content was 0.6 mg, the sample room-temperature resistivity was 6.3×10³ Ω cm, with the Curie point about 135 °C and a high PTC effect of ∼3 orders of magnitude.     

Selective CO oxidation over promoted Au/γ-Al2O3 catalysts in the presence of CO2 and H2O in the feed

In this work, the effect of promoter type (Mg, Mn, Ce, Co, Fe and Ni) on selective CO oxidation performance of Au/γ-Al₂O₃ was studied with the realistic feed stream containing CO₂ and H₂O. The effects of Au loading, promoter loading, reaction temperature and the feed composition were also investigated. It was found that MgO was the best promoter in the presence of CO₂ and H₂O, and 1.25 wt.% Mg was sufficient for promotion. The CO conversion decreased with the addition of CO₂ while the presence of H₂O had some positive effects.     

Co catalysts supported on SiO2 and γ-Al2O3 applied to ethanol steam reforming: Effect of the solvent used in the catalyst preparation method

Cobalt catalysts were prepared on supports of SiO₂ and γ-Al₂O₃ by the impregnation method, using a solution of Co precursor in methanol. The samples were characterized by XRD, TPR, and Raman spectroscopy and tested in ethanol steam reforming. According to the XRD results, impregnation with the methanolic solution led to smaller metal crystallites than with aqueous solution, on the SiO₂ support. On γ-Al₂O₃, all the samples exhibited small crystallites, with either solvent, due to a higher Co-support interaction that inhibits the reduction of Co species. The TPR results were consistent with XRD results and the samples supported on γ-Al₂O₃ showed a lower degree of reduction. In the steam reforming of ethanol, catalysts supported on SiO₂ and prepared with the methanolic solution showed the best H₂, CO₂ and CO selectivity. Those supported on γ-Al₂O₃ showed lower H₂ selectivity.     

Enhancement of pyrolysis gasoline hydrogenation over Zn- and Mo-promoted Ni/γ-Al2O3 catalysts

Alumina-supported nickel catalysts modified by Zn and/or Mo were prepared and characterized using several techniques (XRF, BET, XRD, XPS, and TPR). The effect of Zn and Mo on catalytic hydrogenation activity was evaluated in hydrogenation of pyrolysis gasoline (PyGas) using styrene conversion for monitoring the activity trend in a fixed-bed reactor under the following conditions: temperature of 70–120 °C, H₂:PyGas volume ratio of 200:1, pressure of 2.8 MPa, and volume space velocity of 3.0 h^− 1. The promoted Ni-based catalysts exhibited excellent catalytic activity for the hydrogenation of PyGas. The styrene conversion doubled after the introduction of Zn and Mo.     

Influences of La and Er on structure and properties of Bi2O3–B2O3 glass

Bi₂O₃·2B₂O₃ glasses doped with La₂O₃ and Er₂O₃ were prepared by the melting-quenching method with AR-grade oxides. IR analysis was used to investigate the glass network structure. The characteristic temperatures including the glass transition temperature (T_g), crystallization temperature (T_p), and melting temperature (T_m) were estimated by DSC. The coefficient of thermal expansion (α), mass density (D), and Vickers hardness (H_v) were also measured. The results show that the basic network structure of Bi₂O₃·2B₂O₃ glasses doped with rare-earth oxides consists of chains composed of [BO₃], [BO₄], and [BiO₆] units. La₂O₃ and Er₂O₃ act as network modifiers. As the doping concentrations of the rare-earth oxides were increased, T_g increased and α decreased, indicating that a more rigid glass was obtained. Er₂O₃ reduces the melting temperature and prevents glass crystallization. La₂O₃ contributes to the improvement of the microhardness of Bi₂O₃·2B₂O₃ glass.     

Effect of magnesium addition on catalytic performance of PtSnK/γ-Al2O3 catalyst for isobutane dehydrogenation

The effect of magnesium addition on the catalytic properties of PtSnK/γ-Al₂O₃ catalyst for isobutane dehydrogenation has been investigated by reaction tests and some physicochemical characterizations such as nitrogen adsorption, TEM, H₂ chemisorption, TPR, H₂-TPD, and TPO. It was found that with the suitable addition of magnesium (0.2 and 0.4 wt.%), the platinum dispersion increased, while the carbon depositions decreased. The presence of Mg in the PtSnMgK/γ-Al₂O₃ catalysts could not only strengthen the Sn-Al₂O₃ interaction, but also stabilize the oxidation states of Sn species, which resulted in the increased reaction activity and stability. However, when the content of magnesium was excessive (0.6 and 0.8 wt.%), the character of platinum and the interfacial properties between the metal and the support changed evidently, which was disadvantageous to the reaction. In our experiments, addition of 0.4 wt.% Mg to PtSnK/Al₂O₃ catalyst showed the best catalytic performance. After reaction for 6 h, selectivity toward isobutene of higher than 94% was achieved with the corresponding conversion value of about 29.0%.     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Effect of different nucleation catalysts on the crystallization of Li2O–ZnO–MgO–Al2O3–SiO2 glasses

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO₂, Cr₂O_3, and ZrO₂ on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO₂ > Cr₂O₃ > ZrO₂. Virgilite, β-spodumene ss, gahnite, enstatite and cristobalite were formed in the prepared glass-ceramics. The microstructure of glass-ceramic samples showed growths of rounded and subrounded grains in the base sample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO₂. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO₂ and Cr₂O₃. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr₂O₃ > TiO₂ > ZrO₂) varying from 24.8 × 10⁻⁷ to 65.1 × 10⁻⁷ °C⁻¹ being almost unchanged with the heat-treatment. The microhardness values of glass-ceramic samples were in the 763–779 kg/mm² range.