稀土钙钛矿型催化剂LaBO3对NO催化性能及反应机理的研究（1）

本文作者采用共沉淀法和机械混合法制备了稀土钙钛矿型催化剂ＬａＢＯ３（Ｂ＝Ｔｉ,Ｖ,Ｃｒ,Ｍｎ,Ｆｅ,Ｃｏ,Ｎｉ,ＣＵ）系列稀土钙钛矿型氧化物催化剂,并采用了差热分析（ＤＴＡ）,Ｘ－射线衍射（ＸＲＤ）等技术确定了催化剂制备工艺及条件,同时研究了催化剂对于Ｎ２分解及还原反应的催化活性变化规律。实验结果表明,按确定的制备工艺路线可合成出立方晶系的纯钙钛矿结构,在稀土钙钛矿催化剂ＬａＢＯ３中,Ｂ位离子的     

稀土钙钛矿型催化剂LaBO_3对NO_x催化性能及反应机理的研究(1)——催化剂的合成工艺及催化性能

本文作者采用共沉淀法和机械混合法制备了稀土钙钛矿型催化剂ＬａＢＯ３（Ｂ＝Ｔｉ,Ｖ,Ｃｒ,Ｍｎ,Ｆｅ,Ｃｏ,Ｎｉ,Ｃｕ）系列稀土钙钛矿型氧化物催化剂,并采用了差热分析（ＤＴＡ）、Ｘ－射线衍射（ＸＲＤ）等技术确定了催化剂制备工艺及条件,同时研究了催化剂对于Ｎ２Ｏ分解及还原反应的催化活性变化规律。实验结果表明,按确定的制备工艺路线可合成出立方晶系的纯钙钛矿结构;在稀土钙钛矿催化剂ＬａＢＯ３中,Ｂ位离子的ｄ电子结构决定了催化剂的催化活性。     

稀土钙钛矿型催化剂LaBO_3对NO_x催化性能及反应机理的研究(Ⅱ)──催化剂表面结构及N_2O催化分解反应机理

采用程序升温还原（ＴＰＲ）和Ｘ－光电子能谱（ＸＰＳ）技术研究了稀土钙钛矿型催化剂ＬａＢＯ３上氧种的化学势、Ｂ位元素的平均价态及催化剂氧种的分布及种类,同时分析了Ｎ２Ｏ的分解反应机理。实验结果表明,Ｂ位离子平均价态升高,氧离子的化学势增大,反应能力增强,催化活性较好;在ＬａＢＯ３化合物上有两类氧种,即低能位的吸附氧和高能位的晶格氧,催化剂表面吸附氧对Ｎ２Ｏ分解有阻抑作用,ＣＨ４的加入能与表面吸附氧反应,提供氧空位,促进反应进行;Ｎ２Ｏ在钙钛矿型化合物ＬａＢＯ３上的分解反应属于表面上的催化过程     

稀土钙钛矿型催化剂LaBO3对NOx催化性能及反应机理的研究（Ⅱ …

采用程序升温还原（ＴＰＲ）和Ｘ－光电子能谱（ＸＰＳ）技术研究了稀土钙钛矿型催化剂ＬａＢＯ３,上氧种的化学势、Ｂ位元素的平均价态及催化剂氧种的分布及种类,同时分析了Ｎ２Ｏ的分解反应机理。实验结果表明,Ｂ全离子平均价态升高,氧离子的化学势增大,反应能力增强,催化活性较好;在ＬａＢＯ３化合物上有两类氧种,即低能位的吸附氧和高能位的晶格氧,催化剂表面吸附氧对Ｎ２Ｏ分解有阻抑作用,ＣＨ４的加入能与表面吸附氧     

La2O3对CH4氧化的催化机制

本文研究了Ｌａ２Ｏ３对ＣＨ４氧化燃烧和氧化偶联的催化机制。实验采用的是分子束技术，以及俄歇电子能谱（ＡＥＳ），四极柱质谱（ＱＭＳ）和Ｘ射线光电子能谱（ＸＰＳ）等表面分析技术。实验结果表明ＣＨ４分子的平动能和Ｌａ２Ｏ３表面的晶格氧（Ｏ２－）是催化氧化ＣＨ４的两个关键因素。燃烧室内壁涂以稀土氧化物催化层将会提高燃烧效率和减少废气污染。     

Cdln2O4和Cd2SnO4薄膜X—光电子能谱研究

研究了在Ａｒ－Ｏ２混合气氛中从Ｃｄ－Ｉｎ和Ｃｄ－Ｓｎ合金靶射频反应溅射而的ＣｄＩｎ２Ｏ４和Ｃｄ２ＳｎＯ４膜的Ｘ－光电子能谱。实验结果表明了粉末Ｃｄ，Ｉｎ，Ｓｎ，ＳｎＯ２，Ｉｎ２Ｏ３和ＣｄＩｎ２Ｏ４，Ｃｄ２ＳｎＯ４膜的Ｃｄ，Ｉｎ，Ｓｎ３Ｄ３／２和３ｄ５／２ＸＰＳ峰值位置的形状的区别，并讨论了Ｏ１ｓ。ＸＰＳ峰随氧浓度的变化。当氧浓度增加时，Ｏ１ｓ分为两个峰。     

CdIn_2O_4和Cd_2SnO_4薄膜X－光电子能谱研究

研究了在Ａｒ＋Ｏ２混合气氛中从Ｃｄ－Ｉｎ和Ｏｄ－Ｓｎ合金靶射频反应溅射而成的ＣｄＩｎ２Ｏ４和Ｃｄ２ＳｎＯ４膜的Ｘ－光电子能谱。实验结果表明了粉末Ｃｄ、Ｉｎ、Ｓｎ、ＳｎＯ２、Ｉｎ２Ｏ３和ＣｄＩｎ２Ｏ４、Ｃｄ２ＳｎＯ４膜的Ｃｄ、Ｉｎ、Ｓｎ３ｄ３／２和３ｄ５／２ＸＰＳ峰值位置和形状的区别，并讨论了Ｏ１ｓＸＰＳ峰随氧浓度的变化。当氧浓度增加时，Ｏ１ｓ分为两个峰。     

某些稀土离子对电沉积CdTd薄膜性能影响的研究

ＣｄＴｅ薄膜半导体电极通过电沉积法制备。电沉积溶液组成对ＣｄＴｅ薄膜组成和性能有较大影响，通过在电镀液中添加某些稀土离子，结合ＸＲＤ、ＴＥＭ、ＸＰＳ和光电Ｉ－Ｖ特性曲线进行分析研究，表明电沉积ＣｄＴｅ薄膜存在择优取向，经２５０℃热处理后，晶粒长大，镀液中添加Ｙ＾３＋、Ｌａ＾３＋、Ｃｅ＾３＋和Ｎｄ＾３＋后增大尤为明显，晶粒线性尺寸最大达２．５－３．０×１０＾－７ｍ左右，并伴有孪晶产生，可提高薄膜Ｃｄ     

某些稀土离子对电沉积 CdTe 薄膜性能影响的研究

ＣｄＴｅ薄膜半导体电极通过电沉积法制备。电沉积溶液组成对ＣｄＴｅ薄膜组成和性能有较大影响，通过在电镀液中添加某些稀土离子，结合ＸＲＤ、ＴＥＭ、ＸＰＳ和光电Ｉ－Ｖ特性曲线进行分析研究，表明电沉积ＣｄＴｅ薄膜存在择优取向，经２５０℃热处理后，晶粒长大，镀液中添加Ｙ３＋、Ｌａ３＋、Ｃｅ３＋和Ｎｄ３＋后增大尤为明显，晶粒线性尺寸最大达２．５—３．０×１０－７ｍ左右，并伴有孪晶产生，可提高薄膜Ｃｄ／Ｔｅ比等，有利于提高ＣｄＴｅ光电性能。经测试，其光电转换效率可增大到２．６—３．３％。     

粉煤流化床燃烧中N2O的生成特性

粉煤流化床（ＰＣ－ＦＢ）是一项燃烧效率高,同时实现炉内脱硫,低ＮＯｘ和Ｎ２Ｏ排放的新型高效、清洁煤燃烧技术,在一座０．３ＭＷ的试验台上,研究了其Ｎ２Ｏ生成与分布特性,包括床层温度Ｔｂ、流化速度Ｕｏ、二次风率Ｒ２,ＰＣ－ＦＢ流化床燃烧区（ＦＢＣＺ）出口氧浓度Ｏ２、钙硫化（Ｃａ／Ｓ）对ＦＢＣＺ出口Ｎ２Ｏ浓度的影响;以及各层二次风份额（Ｒ２ｉ％）及悬浮空间燃烧区（ＦＣＺ）的温度分布与炉内Ｎ２Ｏ浓度分布的     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

The Solar Office in context

The goal of sustainability in buildings can only hope to be realised if buildings are designed to both conserve and generate energy. The Solar Office at Doxford International is designed to minimise the use of energy while its external fabric is designed to replace such energy that is used. The recently completed building is now subject of a comprehensive monitoring programme. The programme covers both the performance of the 73 kW_p photovoltaic installation and the environmental conditions within the building as a whole. Hour by hour findings are posted on a dedicated web site. Photovoltaics could have the same impact on building form and layout as the invention of the passenger lift at the end of the last century.     

Hydrogen recovery from the photovoltaic electroflocculation-flotation process for harvesting Chlorella pyrenoidosa microalgae

In this paper, an integrated process using photovoltaic power to harvest microalgae by electro-flocculation (EF) and hydrogen recovery is presented. It is mainly favorable in regions with high solar radiation. The electro-flocculation efficiency (EFE) of Chlorella pyrenoidosa microalgae was investigated using various types of electrodes (aluminum, iron, zinc, copper and a non-sacrificial electrode of carbon). The best results regarding the EFE, and biomass contamination were achieved with aluminum and carbon electrodes where the electrical energy demand of the process for harvesting 1 kg of algae biomass was 0.28 and 0.34 kWh, respectively, while the energy yield of harvested hydrogen was 0.052 and 0.005 kWh kg^?1, respectively. The highest harvesting efficiency of 95.83 ± 0.87% was obtained with the aluminum electrode.The experimental hydrogen yields obtained were comparable with those calculated from theory. With a low net energy demand, microalgae EF may be a useful and low-cost technology.     

Electrochemical behavior of Mg–Li,Mg–Li–Al and Mg–Li–Al–Ce in sodium chloride solution

Mg–Li, Mg–Li–Al and Mg–Li–Al–Ce alloys were prepared and their electrochemical behavior in 0.7 M NaCl solutions was investigated by means of potentiodynamic polarization, potentiostatic current–time and electrochemical impedance spectroscopy measurements as well as by scanning electron microscopy examination. The effect of gallium oxide as an electrolyte additive on the potentiostatic discharge performance of these magnesium alloys was studied. The discharge activities and utilization efficiencies of these alloys increase in the order: Mg–Li < Mg–Li–Al < Mg–Li–Al–Ce, both in the absence and presence of Ga₂O₃. These alloys are more active than commercial magnesium alloy AZ31. The addition of Ga₂O₃ into NaCl electrolyte solution improved the discharging currents of the alloys by more than 4%, and enhanced the utilization efficiencies of the alloys by more than 6%. It also shortened the transition time for the discharge current to reach to a steady value. Electrochemical impedance spectroscopy measurements showed that the polarization resistance of the alloys decreases in the following order: Mg–Li > Mg–Li–Al > Mg–Li–Al–Ce. Mg–Li–Al–Ce exhibited the best performance in term of activity, utilization efficiency and activation time.     

Temperature dependence of the enthalpy of formation of metal hydrides characterized by an excess volume

A universal framework to calculate the temperature dependence of the excess enthalpy present in regions characterized by an excess volume is calculated for metals and metal hydrides. At high temperatures, the different contributions from the pressure–volume, heat capacity, entropy and work associated with the thermal expansion are studied separately and their magnitudes and signs are compared. It is found that the pressure–volume contribution opposes and dominates the other three contributions at both high temperature and excess volume, and it is thus found that this contribution becomes the leading temperature dependent contribution to the enthalpy of a material. The conditions under which a temperature change will reduce the enthalpy of formation of metal hydrides are also given and the Mg/MgH₂ system is studied as an example. Excluding the heat capacity contribution, an increase in temperature tends to offset the effect of the excess volume on the enthalpy of formation. It is also demonstrated that the impact of temperature will be more favorable to a reduction of the enthalpy of formation if a large fraction of the metal hydride is in a state of small excess volume compared to a small fraction of the hydride in a state of high excess volume.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Tailored solar optics for maximal optical tolerance and concentration

Recently identified fundamental classes of dual-mirror double-tailored nonimaging optics have the potential to satisfy the pragmatic exigencies of concentrator photovoltaics. Via a comprehensive survey of their parameter space, including raytrace verification, we identify champion high-concentration high-efficiency designs that offer unprecedented optical tolerance (i.e., sensitivity to off-axis orientation) - a pivotal figure-of-merit with a basic bound that depends on concentration, exit angle, and effective solar angular radius. For comparison, results for the best corresponding dual-mirror aplanatic concentrators are also presented.