Effect of mineralizers for preparing ZrO2 support on the supported Ni catalyst for steam-CO2 bi-reforming of methane

Supported Ni catalysts on ZrO₂ towards steam-CO₂ bi-reforming (SCBR) of methane for the production of synthesis gas were synthesized by the hydrothermal process with different mineralizers followed by l-arginine ligand-assisted incipient wetness impregnation (HT-LA-IWI) method. The effect of type and amount of mineralizers for preparing ZrO₂ supports on the nature of supports and supported Ni catalysts, as well as on the catalytic properties and structure–performance relationship were investigated. Results show that the catalytic performance is strongly dependent on the morphology and textural of ZrO₂ support notably affected by the type and amount of mineralizer. The supported Ni catalyst on the ZrO₂ prepared by using sodium acetate (molar ratio of sodium acetate/zirconium, N_SAc/Zr = 0.5) as mineralizer (Ni/ZrO₂ (SAc0.5)) shows much higher catalytic activity than the one on ZrO₂ prepared by using sodium carbonate (molar ratio of sodium carbonate/zirconium, N_SC/Zr = 0.5) as a mineralizer (Ni/ZrO₂ (SC0.5)), ascribed to higher Ni dispersion and smaller average crystallite size of Ni. With respect to both activity and stability, the sodium acetate can be selected as a suitable mineralizer for the preparation of excellent ZrO₂ support. Furthermore, the increasing N_SAc/Zr from 0.5 to 2.0 leads to an increase in surface area but a decrease in pore diameter and pore volume, which endows the Ni/ZrO₂ (SAc2.0) catalyst with much larger average crystallite size of Ni but much worse Ni dispersion than Ni/ZrO₂ (SAc0.5). As a result, Ni/ZrO₂ (SAc2.0) shows much lower catalytic activity than Ni/ZrO₂ (SAc0.5). Moreover, the Ni/ZrO₂ (SAc2.0) catalyst shows worse Ni sintering resistance than Ni/ZrO₂ (SAc0.5) owing to its weaker NiZrO₂ interaction confirmed by H₂-TPR results, which endows it with lower catalytic stability although it has higher coke deposition resistance.     

Synthesis and electrochemical properties of Li[Li(1−2x)/3NixMn(2−x)/3]O2 as cathode materials for lithium secondary batteries

Layered Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ materials with x=0.41, 0.35, 0.275 and 0.2 are synthesized by means of a sol–gel method. The layered structure is stabilized by a solid solution between LiNiO₂ and Li₂MnO₃. The discharge capacity increases with increasing lithium content at the 3a sites in the Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂. A Li[Li_0.2Ni_0.2Mn_0.6]O₂ electrode delivers discharge capacities of 200 and 240 mAh g⁻¹ with excellent cycleability at 30 and 55 °C, respectively.     

Thermodynamic development and design of a concentrating solar thermochemical water-splitting process for co-production of hydrogen and electricity

A concentrating solar plant is proposed for a thermochemical water-splitting process with excess heat used for electricity generation in an organic Rankine cycle. The quasi-steady state thermodynamic model consisting of 23 components and 45 states uses adjustable design parameters to optimize hydrogen production and system efficiency. The plant design and associated thermodynamic model demonstrate that cerium oxide is suitable for thermochemical water-splitting cycles involving the co-production of hydrogen and electricity. Design point analyses at 900 W/m² DNI indicate that a single tower with solar radiation input of 27.74 MW and an aperture area of 9.424 m² yields 10.96 MW total output comprised of 5.55 MW hydrogen (Gibbs free energy) and 5.41 MW net electricity after subtracting off 22.0% of total power generation for auxiliary loads. Pure hydrogen output amounts to 522 tonne/year at 20.73 GWh/year (HHV) or 17.20 GWh/year (Gibbs free energy) with net electricity generation at 14.52 GWh/year using TMY3 data from Daggett, California, USA. Annual average system efficiency is 38.2% with the constituent hydrogen fraction and electrical fraction being 54.2% and 45.8%, respectively. Sensitivity analyses illustrate that increases in particle loop recuperator effectiveness create an increase in hydrogen production and a decrease in electricity generation. Further, recuperator effectiveness has a measurable effect on hydrogen production, but has limited impact on total system efficiency given that 81.1% of excess heat is recuperated within the system for electricity generation.     

Alkali insertion within NiONi electrode in contact with molten Li2CO3K2CO3 and Li2CO3Na2CO3K2CO3 at 650°C

Lithium, sodium and potassium species have been analysed by different spectroscopic techniques in the NiO layer recovering nickel cathode used in the state-of-the-art molten carbonate fuel cell. The nickel electrode was previously oxidized in lithium-containing carbonate electrolytes, Li₂CO₃K₂CO₃ and Li₂C0₃Na₂CO₃K₂CO₃ at 650°C. Similarly to the well-known case of lithium, it has been shown that the presence of sodium and potassium cations could be associated to their insertion in the NiO lattice.     

Kinetics and mechanism of CO2 gasification of coal catalyzed by Na2CO3, FeCO3 and Na2CO3–FeCO3

The purpose is to develop a mild catalytic CO₂-gasification technology that can promote CO₂ utilization and reduce cost in air separation systems with improving system efficiency and obtaining desirable gaseous products. In this study, the influence of Na, Fe and their composite catalysts on the structure and gasification reactivity of chars derived from pyrolysis of Powder River Basin (PRB) coal was investigated. The results showed that a strong positive synergistic effect between Na and Fe catalyst in the gasification process was observed, the catalytic activity of the added catalysts was in order of: 4% Na > 3% Na–1%Fe > 2% Na-2% Fe > 1% Na-3% Fe > 1% Na-2% Fe > 4% Fe > raw coal. The catalysts inhibited the growth of the aromatic ring structure and enriched the generation of O-containing functional groups. Compared to Fe, the Na-based catalyst could easily diffuse into inner pores of coal char, forming C–O–Na structure and thus increasing the gasification reactivity of chars. In addition, due to the formation of inert material between SiO₂ and Na, the catalytic activity of Na catalysts was significantly decrease at the late stage of char conversion. Comparatively, the Fe-based catalysts showed better stability life. Moreover, it was found that the activation energy for CO₂-gasification of PRB coal can be decreased by 50% due to the addition of Na catalyst.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/Al2O3–ZrO2 xerogel catalysts: Effect of calcination temperature of Al2O3–ZrO2 xerogel supports

Al₂O₃–ZrO₂ (AZ) xerogel supports prepared by a sol-gel method were calcined at various temperatures. Ni/Al₂O₃–ZrO₂ (Ni/AZ) catalysts were then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AZ supports on the catalytic performance of Ni/AZ catalysts in the steam reforming of LNG was investigated. Crystalline phase of AZ supports was transformed in the sequence of amorphous γ-Al₂O₃ and amorphous ZrO₂ → θ-Al₂O₃ and tetragonal ZrO₂ → (θ + α)-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ → α-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ with increasing calcination temperature from 700 to 1300 °C. Nickel oxide species were strongly bound to γ-Al₂O₃ and θ-Al₂O₃ in the Ni/AZ catalysts through the formation of solid solution. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AZ supports. Nickel surface area of Ni/AZ catalysts was well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni/AZ1000 (nickel catalyst supported on AZ support that had been calcined at 1000 °C) with the highest nickel surface area showed the best catalytic performance. Well-developed and pure tetragonal phase of ZrO₂ in the AZ1000 support played an important role in the adsorption of steam and the subsequent spillover of steam from the support to the active nickel.     

Li2CO3-Na2CO3-K2CO3相图的理论预测

熔盐是一种重要的聚光太阳能系统传热流体,多元熔盐混合是满足实际需求的有效方法,而熔盐混合物的相图是其筛选的主要因素之一.该文基于热力学原理及吉布斯自由能对Li2CO3-Na2CO3-K2CO3的相图进行预测与计算,结果显示:该熔盐混合物的共晶点为421.2℃,Li2CO3、Na2CO3和K2CO3的质量分数分别为25....     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

Fabrication of MgTiO3 nanofibers by electrospinning and their photocatalytic water splitting activity

The photocatalytic H₂ evolution from water splitting is a promising process for generating renewable energy. In regard of the fascinating properties of the one-dimensional (1D) nanostructure, when used as photocatalyst, we report the synthesis of MgTiO₃ 1D nanofibers by the electrospinning technique and the investigations of their photocatalytic performance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) corporately confirmed the successful fabrication of pure MgTiO₃ nanofibers. By contrast, the MgTiO₃ nanoparticles obtained via sol-gel method still contains impurities because of the inhomogeneous crystallization. The MgTiO₃ nanofibers exhibited enhanced efficiency and stability in photocatalytic H₂ generation under ultraviolet light, compared with the MgTiO₃ nanoparticles and P25. The photoelectrochemical measurements further revealed that MgTiO₃ nanofibers facilitated the transport and separation of the photoinduced charge carriers, mainly resulting from their special 1D structure, unique mesh morphology, large specific surface area and pure phase.     

Transformation and release of potassium during fixed-bed pyrolysis of biomass

To study the release and transformation of fuel K during rapid pyrolysis of biomass, wheat straw, corn stalk and rice hull are pyrolyzed in a fixed-bed reactor system during 400–1000 °C, and weight measurement, elemental composition analysis, and chemical fractionation analysis are performed. The effects of fuel type, pyrolysis temperature, co-pyrolysis of different fuels, and water washing pretreatment are discussed. The results show that for all biomass fuels, the released K is far less than the water-soluble K and a sudden increase occurs in the fraction of ion-exchangeable K at 400 °C, whereas a significant increase happens in the fraction of insoluble K above 800 °C. Wheat straw releases less than 5% of K at 400 and 500 °C. As temperature rises, the K release increases abruptly and around 40% of K enters the gas phase at 1000 °C. Rice hull has a slow and linear K release with increasing pyrolysis temperature. Corn stalk has the lowest K release during 400–800 °C. Co-pyrolysis of wheat straw and rice hull reduce the K release at 1000 °C, and the biggest decrement is 0.76 mg g^?1. Water washing removes all the water-soluble K of corn stalk and part of ion-exchangeable K enters the gas phase during pyrolysis of the washed sample. Water washing decreases the K release from 2.77 to 0.18 mg g^?1 at 1000 °C.     

Achievement of hydrogen production from autothermal steam reforming of methanol over Cu-loaded mesoporous CeO2 and Cu-loaded mesoporous CeO2–ZrO2 catalysts

Hydrogen production by oxidative steam reforming of methanol (OSRM) or autothermal steam reforming of methanol (ASRM) was investigated over Cu-loaded mesoporous CeO₂ and Cu-loaded mesoporous CeO₂–ZrO₂ catalysts, synthesized via a nanocasting process using MCM-48 as a hard template, followed by a deposition–precipitation technique. Various Cu contents were loaded on the mesoporous CeO₂ and CeO₂–ZrO₂ supports. The fresh and spent catalysts were characterized by N₂ adsorption–desorption, X-ray diffraction, temperature-programmed oxidation, and X-ray photoelectron spectroscopy. The ASRM results showed that 9 wt% Cu loading onto mesoporous CeO₂ and CeO₂–ZrO₂ provided the best catalytic performance with 100% methanol conversion and 60% H₂ yield at 350° and 300 °C, respectively. Furthermore, the time-on-stream stability testing of the 9 wt% Cu loading catalyst was at 168 h, and the CO selectivity of these two catalysts indicated that the addition of ZrO₂ into the catalyst reduced the CO selectivity during the ASRM process.     

Recyclable CeO2–ZrO2 and CeO2–TiO2 mixed oxides based Pt catalyst for aqueous-phase reforming of the low-boiling fraction of bio-oil

In this study, a series of CeO₂–ZrO₂ and CeO₂–TiO₂ materials with different composition were prepared, characterized by BET and XRD analysis, and their hydrothermal stability was studied by subjecting the samples to acetic acid solutions at 533 K. All of the materials, especially C1Z1 (50 mol% CeO₂ with 50 mol% ZrO₂) and C1T1 (50 mol% CeO₂ with 50 mol% TiO₂), exhibited excellent stability with no phase transformation and minimal decrease in their specific surface area (SSA) was observed even after 16 h. After being loaded by Pt, these catalysts were used for the aqueous phase reforming (APR) of the low-boiling fraction of bio-oil (LBF) to investigate their catalytic performance. Among these catalysts Pt/C1Z1 and Pt/C1T1 showed superior catalytic activity, probably due to their lowest reduction temperature and the largest amount of O vacancies generated by the reduction of the surface oxygen of well-dispersed CeO₂. Thus, Pt/C1Z1 and Pt/C1T1 were chosen to investigate their recyclability. The catalytic activity and H₂ selectivity of Pt/C1Z1 and Pt/C1T1 can be almost recovered after being calcined in air at 773 K for regeneration. After three cycles, the particle size of Pt/C1Z1 and Pt/C1T1 only experienced a slight increase, while for Pt/Al₂O₃ it increased from 2.9 nm to 7.8 nm. So, compared with Pt/Al₂O₃, the Pt/C1Z1 and Pt/C1T1 catalysts were identified as effective and recyclable candidates for the production of H₂ rich fuel gas from APR of LBF.     

On the growth of Li2CO3 dendrites in nickel–cadmium industrial batteries

A large amount of Li₂CO₃ dendrites has been detected on positive electrodes in Ni–Cd industrial pocket plate batteries, intended to work in stationary applications, after 3 years in float charge. The lattice parameters were refined to a=8.353(1) Å, b=4.974(1) Å, c=6.194(1) Å and β=114.6(1)° [monoclinic], which is in complete agreement with structural data reported in the literature. Oxidation of graphite present in the positive active material is enhanced at elevated temperatures, and at high anodic potentials. This results in an extremely high carbonate concentration in the active material, as well as in the electrolyte. The high carbonate content, in combination with the relatively high lithium concentration present in both electrolyte and positive electrode, is very likely to be the reason for the formation of the Li₂CO₃ dendrites. As this process continues, agglomerates of the dendrites in combination with attached β-Cd(OH)₂ and graphite may generate short circuits between the positive and the negative electrodes.     

ZrO2增强MoSi2复合材料

本文叙述了采用热压工艺制备的ＺｒＯ２－ＭｏＳｉ２二相复合材料；研究表明：复合材料随着ＺｒＯ２含量的增加，其硬度和断裂韧性的增大；同时就ＺｒＯ２颗粒对ＭｏＳｉ２基体的强化效果进行了分析。     

The influence of the addition of sodium on the transformation of alkali and alkaline-earth metals during oxy-fuel combustion

Alkali and alkaline-earth metals (AAEM) of coal directly affect the coal combustion properties and ash formation during coal oxy-fuel combustion. To further understand the influence of adding sodium on the transformation of AAEM, sodium chloride (NaCl) and sodium acetate (NaAc) were added to Shenmu coal in this study. A drop-tube reactor and ion chromatography were adopted in this study and a serial dissolution method was used to clarify the occurrence modes of the AAEM. The results showed that all types of AAEM can release and the release rates were increased with an increase in temperature during oxy-fuel combustion. Water-soluble (W-type) alkali metals react with SiO₂ and Al₂O₃ in coal and are converted into acid-soluble (H-type) silicate or acid-insoluble (I-type) aluminosilicate under certain experimental conditions. The addition of sodium can promote the release of AAEM via promoting coal combustion; the promotion effect was significant at 600 °C, and the effect of NaCl was more noticeable than that of NaAc. Furthermore, the promoting effect on alkali metals was more noticeable than that on alkali-earth metals. The added sodium can also react with SiO₂ and Al₂O₃ to form H-type sodium silicate or I-type sodium aluminosilicate.     

Effects of CaO addition on Ni/CeO2–ZrO2–Al2O3 coated monolith catalysts for steam reforming of N-decane

A series of 10 wt%Ni/CeO₂–ZrO₂–Al₂O₃ (10%Ni/CZA) coated monolith catalysts modified by CaO with the addition amount of 1 wt%~7 wt% are prepared by incipient-wetness co-impregnation method. Effects of CaO promoter on the catalytic activity and anti-coking ability of 10%Ni/CZA for steam reforming of n-decane are investigated. The catalysts are characterized by N₂ adsorption-desorption, XRD, SEM-EDS, TEM, NH₃-TPD, XPS, H₂-TPR and Raman. The results show that specific surface area and pore volume of as-prepared catalysts decrease to some extent with the increasing addition of CaO. However, the proper amounts of CaO (≤3 wt%) significantly enhance the catalytic activity in terms of n-decane conversion and H₂ selectivity mainly due to the improved dispersion of NiO particles (precursor of Ni particles). As for anti-coking performance, reducibility of CeO₂ in composite oxide support CZA is promoted by CaO resulting in providing more lattice oxygen, which favors suppressing coke formation. Moreover, the addition of CaO reduces the acidity of 10%Ni/CZA, especially the medium and strong acidity. But far more importantly, a better dispersion of NiO particles obtained by proper amounts of CaO addition is dominant for the lower carbon formation, as well as the higher catalytic activity. For the spent catalysts, amorphous carbon is the main type of coke over 10%Ni–3%CaO/CZA, while abundant filamentous carbon is found over the others.     

Modeling of direct carbon solid oxide fuel cells with H2O and CO2 as gasification agents

In this paper, 2D models for direct carbon solid oxide fuel cells (DC-SOFCs) with H₂O and CO₂ as agents for carbon gasification are developed. The simulation results are compared with experimental data and good agreement is obtained. The performance of DC-SOFCs with two agents is compared at different operating potential, temperature and anode inlet gas flow rate. It is found that the H₂O assisted DC-SOFC performs significantly better than the CO₂-assisted DC-SOFC, indicating the suitability of H₂O for DC-SOFCs. It is also found that a higher temperature could greatly improve the performance of both kinds of DC-SOFCs. At a temperature of 1000 K and operating voltage of 0.5 V, the current density from the CO₂-assisted DC-SOFC is close to 0 while it is still above 1000 A m^?2 from the H₂O-assisted DC-SOFC, indicating the possibility of operating the H₂O assisted DC-SOFC at reduced temperature. It is found that the anode gas flow rate does not significantly affect the performance of DC-SOFC. To further improve the performance of H₂O assisted DC-SOFCs, developing suitable catalysts for enhancing carbon gasification kinetics could be a good strategy. The results of this study form a solid foundation to understand H₂O assisted DC-SOFCs.     

High hydrogen selectivity and anti-carbon ability by cracking of RP-3 jet fuel over Pt/ZrO2–TiO2–Al2O3 catalyst modified by MxOy (M = Ba,Sr and Ce) promoters

In order to improve the anti-carbon property and obtain higher H₂ yields, the promoters (BaO, SrO and CeO₂) were introduced into Pt/ZrO₂–TiO₂–Al₂O₃ catalyst. The activity of theses catalysts were investigated in the cracking reactions of RP-3 jet fuel under high temperature and high pressure conditions. The physicochemical characteristics of the catalysts were detected by Temperature programmed oxidation, Raman spectrum, N₂ adsorption–desorption, Transmission electron microscope, NH₃-temperature programmed desorption and NH₃-infrared spectroscopy techniques. It was found that the addition of BaO, SrO and CeO₂ promoted the well dispersion of Pt, stimulated the dehydrogenation reactions, and consequently higher hydrogen yields over modified catalysts were obtained. Moreover, the acid sites have been partially neutralized by these promoters, thus the total amount of acid sites as well as the Lewis acid sites decreased over the modified catalysts. The modified acidic properties inhibited the hydrogen transfer reactions and alkenes oligomerization reactions, resulting in the obvious decrease of carbon deposit. Therefore, the catalysts exhibited remarkable anti-carbon property after modifying by BaO, SrO and CeO₂. The valuable information in this work may be helpful to develop highly efficient catalysts for the advanced aircrafts.