Thermophysical properties and devitrification of SrO–La2O3–Al2O3–B2O3–SiO2-based glass sealant for solid oxide fuel/electrolyzer cells

Thermal behaviors and stability of glass/glass–ceramic-based sealant materials are critical issues for high temperature solid oxide fuel/electrolyzer cells. To understand the thermophysical properties and devitrification behavior of SrO–La₂O₃–Al₂O₃–B₂O₃–SiO₂ system, glasses were synthesized by quenching (25 − X)SrO–20La₂O₃–(7 + X)Al₂O₃–40B₂O₃–8SiO₂ oxides, where X was varied from 0.0 mol% to 10.0 mol% at 2.5 mol% interval. Thermal properties were characterized by dilatometry and differential scanning calorimetry (DSC). Microstructural studies were performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). All the compositions have a glass transition temperature greater than 620 °C and a crystallization temperature greater than 826 °C. Also, all the glasses have a coefficient of thermal expansion (CTE) between 9.0 × 10⁻⁶ K⁻¹ and 14.5 × 10⁶ K⁻¹ after the first thermal cycle. La₂O₃ and B₂O₃ contribute to glass devitrification by forming crystalline LaBO₃. Al₂O₃ stabilizes the glasses by suppressing devitrification. Significant improvement in devitrification resistance is observed as X increases from 0.0 mol% to 10.0 mol%.     

Plasma-reduced Ni/γ–Al2O3 and CeO2–Ni/γ–Al2O3 catalysts for improving dry reforming of propane

Pristine Ni/γ–Al₂O₃ and CeO₂–Ni/γ–Al₂O₃ catalysts were prepared by co-impregnation technique for dry reforming of propane. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to examine the structure and morphology of the catalysts before and after the reforming reactions. The excellent interaction between catalyst active phases was observed in both CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃ stabilized with polyethelene glycol (Ni/γ–Al₂O₃–PEG). Towards C₃H₈ and CO₂ conversion, the CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃–PEG showed improved catalytic activity when compared to the pristine Ni/γ–Al₂O₃ catalyst. Interestingly, high H₂ concentration was achieved with the CeO₂–Ni/γ–Al₂O₃ and high CO concentration with the Ni/γ–Al₂O₃–PEG, which is due to the nanoconfinement of nickel particles within the support and favorable metal-support interaction as a result of plasma reduction. The CeO₂–Ni/γ–Al₂O₃ catalyst exhibited better stability for anti-sintering and coke resistance, thus exhibiting high reactivity and durability in the dry reforming.     

Metal-supported solid oxide fuel cells with in-situ sintered (Bi2O3)0.7(Er2O3)0.3–Ag composite cathode

Metal-supported solid oxide fuel cells (SOFCs) containing porous 430L stainless steel support, Ni-YSZ anode and YSZ electrolyte were fabricated by tape casting, laminating and co-firing in a reduced atmosphere. (Bi₂O₃)_0.7(Er₂O₃)_0.3–Ag composite cathode was applied by screen printing and in-situ sintering. The polarization resistances of the composite cathode were 1.18, 0.48, 0.18, 0.09 Ω cm² at 600, 650, 700 and 750 °C, respectively. A promissing maximum power density of 568 mW cm⁻² at 750 °C was obtained of the single cell. Short-term stability was measured as well.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Effect of B2O3–Bi2O3–PbO frit on the performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The effects of B₂O₃–Bi₂O₃–PbO (BBP) frit on the electrochemical performance, electrical conductivity, and thermal expansion of LaBaCo₂O_5+δ (LBCO) cathode were investigated. BBP frit was found to be effective in lowering the sintering temperature of LBCO cathode by about 200 °C and in improving its electrochemical performance within the intermediate-temperature range of 600–800 °C. LBCO with 5 wt.% BBP frit cathode based on Sm_0.2Ce_0.8O_1.9 electrolyte showed the best electrochemical performance, i.e., the lowest area-specific resistance (ASR) and cathodic overpotential. The ASR values were about 64.1%, 66.1%, and 74.5% lower than those of LBCO at 700, 750, and 800 °C, respectively. The cathodic overpotential decreased from 51.0 mV for LBCO to 8.2 mV at a current density of 0.2 A cm⁻² at 700 °C. The electrical conductivity of LBCO with 5 wt.% BBP frit was about 320–330 S cm⁻¹ at 600–800 °C in air.     

Ag/Al2O3(Li2O)/g-C3N4光催化乙醇制取环氧乙烷

本文制备了一系列Ag/Al₂O₃(Li₂O)/g-C₃N₄复合催化剂,考察了其可见光催化乙醇制取环氧乙烷的性能。Li₂O可调变Al₂O₃表面的酸性,从而降低了主要副产物乙醛的选择性。Ag/Al₂O₃(Li₂O) 在g-C₃N₄上的负载量对产物环氧乙烷的选择性有较大影响,当Ag/Al₂O₃(Li₂O) 负载量为5wt%时,乙醇具有较高的转换率,且环氧乙烷的选择性高达100%。     

(La0.74Bi0.10Sr0.16)MnO3−δ–(Bi2O3)0.7(Er2O3)0.3 composite cathodes for intermediate temperature solid oxide fuel cells

(La_0.74Bi_0.10Sr_0.16)MnO_3−δ (LBSM)–(Bi₂O₃)_0.7(Er₂O₃)_0.3(ESB) composite cathodes were fabricated for intermediate-temperature solid oxide fuel cells with Sc-stabilized zirconia as the electrolyte. The performance of these cathodes was investigated at temperatures below 750 °C by AC impedance spectroscopy and the results indicated that LBSM–ESB had a better performance than traditional composite electrodes such as LSM–GDC and LSM–YSZ. At 750 °C, the lowest interfacial polarization resistance was only 0.11 Ω cm² for the LBSM–ESB cathode, 0.49 Ω cm² for the LSM–GDC cathode, and 1.31 Ω cm² for the LSM–YSZ cathode. The performance of the cathode was improved gradually by increasing the ESB content, and the performance was optimal when the amounts of LBSM and ESB were equal in composite cathodes. This study shows that the sintering temperature of the cathode affected performance, and the optimum sintering temperature for LBSM–ESB was 900 °C.     

Effects of Y2O3-modification to Ni/γ-Al2O3 catalysts on autothermal reforming of methane with CO2 to syngas

The effects of Y₂O₃-modification to Ni/γ-Al₂O₃ catalysts on autothermal reforming of methane to syngas were investigated. It was found that the introduction of Y₂O₃ (5%, 8%, 10%) lead to significant improvement in catalytic activity and stability, and the H₂/CO ratio could be adjusted via controlling the O₂/CO₂ ratio of the feed gas. According to the characterization results of catalysts before and after reaction, it was found that the Y₂O₃·γ-Al₂O₃ supported Ni catalysts had higher NiO reducibility, smaller Ni particle size, higher Ni dispersion and stronger basicity than those of the Ni/γ-Al₂O₃ catalysts. The analysis of catalysts after reaction showed that the addition of Y₂O₃ inhibited the Ni sintering, changed the type of coke and decreased the amount of coke on the catalysts. All the experimental results indicated that the introduction of Y₂O₃ to Ni/γ-Al₂O₃ resulted in excellent catalytic performances in autothermal reforming of methane, and Y₂O₃ played important roles in preventing metal sintering and coke deposition via controlling NiO reducibility, Ni particle size and dispersion, and basicity of catalysts.     

Catalysts of Ni/α-Al2O3 and Ni/La2O3-αAl2O3 for hydrogen production by steam reforming of bio-oil aqueous fraction with pyrolytic lignin retention

This paper reports on the steam reforming, in continuous regime, of the aqueous fraction of bio-oil obtained by flash pyrolysis of lignocellulosic biomass (sawdust). The reaction system is provided with two steps in series: i) thermal step at 200 °C, for the pyrolytic lignin retention, and ii) reforming in-line of the treated bio-oil in a fluidized bed reactor, in the range 600–800 °C, with space-time between 0.10 and 0.45 g_catalyst h (g_bio-oil)⁻¹. The benefits of incorporating La₂O₃ to the Ni/α-Al₂O₃ catalyst on the kinetic behavior (bio-oil conversion, yield and selectivity of hydrogen) and deactivation were determined. The significant role of temperature in gasifying coke precursors was also analyzed. Complete conversion of bio-oil is achieved with the Ni/La₂O₃-αAl₂O₃ catalyst, at 700 °C and space-time of 0.22 g_catalyst h (g_bio-oil)⁻¹. The catalyst deactivation is low and the hydrogen yield and selectivity achieved are 96% and 70%, respectively.     

Nanostructured palladium–La0.75Sr0.25Cr0.5Mn0.5O3/Y2O3–ZrO2 composite anodes for direct methane and ethanol solid oxide fuel cells

A palladium-impregnated La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ/yttria-stabilized zirconia (LSCM/YSZ) composite anode is investigated for the direct utilization of methane and ethanol fuels in solid oxide fuel cells (SOFCs). Impregnation of Pd nanoparticles significantly enhances the electrocatalytic activity of LSCM/YSZ composite anodes for the methane and ethanol electrooxidation reaction. At 800 °C, the maximum power density is increased by two and eight times with methane and ethanol fuels, respectively, for a cell with the Pd-impregnated LSCM/YSZ composite anode, as compared with that using a pure LSCM/YSZ anode. No carbon deposition is observed during the reaction of methane and ethanol fuels on the Pd-impregnated LSCM/YSZ composite anode. The results show the promises of nanostructured Pd-impregnated LSCM/YSZ composites as effective anodes for direct methane and ethanol SOFCs.     

Hydrogen production by biomass gasification in supercritical water over Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts. The catalytic activity and H₂ selectivity of Ni/CeO₂-γAl₂O₃ was higher than that of Ni/γ-Al₂O₃ catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO₂-γAl₂O₃ catalyst had a certain role in the inhibition of carbon deposition and coking.     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Nano-magnetic catalyst KF/CaO–Fe3O4 for biodiesel production

A nano-magnetic catalyst KF/CaO–Fe₃O₄ was prepared by a facile impregnation method. The magnetic property of the catalyst was studied by vibrating sample magnetometer (VSM). The results demonstrated that the catalyst was ferromagnetic, and it could be recovered by magnetic separation. The nano-magnetic catalyst was also characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface area analyzer. It was found that the catalyst possessed a unique porous structure with an average particle diameter of ca. 50 nm. Besides, the factors affecting biodiesel yield were investigated, and a desired fatty acid methyl esters yield over 95% was obtained under the optimal conditions.     

Novel Ni–ZrO2 catalyst doped with Yb2O3 for ethanol steam reforming

A type of Yb₂O₃ doped Ni–ZrO₂ catalyst for ethanol steam reforming was developed, and displayed excellent catalyzing performance for the selective formation of H₂ and CO₂. Over a Ni_1.25Zr₁Yb_0.8 catalyst, STY(H₂) can maintain stable at the level of 0.396 mol h⁻¹ g⁻¹ (data taken 120 h after the reaction started) under the reaction conditions of 0.5 MPa and 723 K, which was 1.6 times that (0.247 mol h⁻¹ g⁻¹) of the Yb-free counterpart Ni_1.25Zr₁. Characterization of the catalyst revealed that dissolution of an appropriate amount of Yb³⁺ ions in the zirconia host resulted in the formation of the Zr–Yb composite oxide with cubic-ZrO₂ structure, c-(Zr–Yb)O_z, which inhibited effectively the transformation of c-ZrO₂ to thermodynamically more stable m-ZrO₂, thus avoiding sintering of the (Zr–Yb)O_z composite. It was demonstrated that the doping of Yb₂O₃ to Ni–ZrO₂ changed also the valence states or the micro-environments of the Ni-species at the quasi-active surface of the tested catalyst, which was conducive to inhibiting agglomeration of the Ni_x⁰–Niⁿ⁺ species active catalytically, with resulting in maintaining the high metallic nickel dispersion and inhibiting coking. The aforementioned two factors both contributed to improving the activity and operating stability as well as heat-resistant quality of the catalyst.     

Performance stability of impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ–Y2O3 stabilized ZrO2 cathodes of intermediate temperature solid oxide fuel cells

The stability of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ impregnated Y₂O₃ stabilized ZrO₂ (LSCF–YSZ) cathodes was investigated under the condition of open circuit or current polarization at 750 °C in air. The electrochemical measurement and the microstructure characteristic show that the flattening of LSCF particles has great contribution to the increase of resistance of LSCF–YSZ cathodes after 500 h heat treatment at 750 °C. Microstructure coarsening and the damage of well-connected porous structure are main reasons of the performance degradation for LSCF–YSZ cathodes testing at 200 mA cm⁻² and 750 °C in air. Higher current density of 500 mA cm⁻² applying on cathodes accelerates degradation processes. X-ray photoelectron spectroscopy (XPS) shows that Sr concentration on the cathode surface decreases after current polarization, which plays a main role in performance activation processes observed at the beginning stage. The enhancement of cobalt activity in LSCF lattice by current polarization increases the conductivity and decreases the stability of LSCF–YSZ cathodes.     

Performance of large-scale anode-supported solid oxide fuel cells with impregnated La0.6Sr0.4Co0.2Fe0.8O3−δ+Y2O3 stabilized ZrO2 composite cathodes

Anode-supported planar solid oxide fuel cells (SOFCs) with an active area of 81 cm² (9 cm × 9 cm) and nano-structured La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ + Y₂O₃ stabilized ZrO₂ (LSCF + YSZ) composite cathodes are successfully fabricated by tape casting, screen printing, co-firing and solution impregnation, and tested using H₂ fuel and air oxidant at various flow rates. Maximum power densities of 437 and 473 mW cm⁻² are achieved at 750 °C by loading 0.6 and 1.3 mg cm⁻² of LSCF in the composite cathodes, respectively. The gas flow rates, particularly the air, have a significant effect on the cell performance. Cell performance degradation with time is also observed, which is considered to be associated with the growth and coalescence of the nanosized LSCF particles in the composite cathode. The use of the LSCF cathode in combination with YSZ electrolyte without a Gd-doped CeO₂ (GDC) buffer layer is proved to be applicable in large cells, even though the thermal stability of the nanosized LSCF needs to be further improved.     

Syngas production by CO2 reforming of coke oven gas over Ni/La2O3–ZrO2 catalysts

Syngas production by CO₂ reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La₂O₃–ZrO₂ catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H₂-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La₂O₃–ZrO₂ catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH₄ and CO₂ both more than 95% at 800 °C under the atmospheric pressure. The Ni/La₂O₃–ZrO₂ catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO₂ reforming of COG in the future.     

CO2 reforming of CH4 by combination of cold plasma jet and Ni/γ-Al2O3 catalyst

CO₂ reforming of CH₄ to synthesis gas was investigated by cold plasma jet (CPJ) only and combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst at atmospheric pressure. The higher selectivity of H₂ and CO, and higher energy efficiency was obtained by this novel process. The optimum experimental conditions are: CH₄ = 3.33 Nl/min, CO₂ = 5.00 Nl/min, N₂ = 8.33 Nl/min, and the input power at 770 W. The results showed that, for the plasma only, the conversions of CH₄ and CO₂ were 46% and 34%, the selectivities of CO and H₂ were 85% and 78%, the energy efficiency was 2.9 mmol/kJ, respectively; for the combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst, the conversions of CH₄ and CO₂ were increased by 14% and 6%, the yield of H₂ and CO increased by 18% and 11%, the energy efficiency reached at 3.7 mmol/kJ, respectively. And the catalyst hasn't accessorial heating. The CPJ method has the advantage of simple processing and is easy to be industrialized.