WO_3/TiO_2-ZrO_2催化剂的高温脱硝性能

以复合氧化物TiO_2-ZrO_2为载体、WO_3为活性组分,制备了适用于高温烟气(500℃以上)脱硝的WO_3/TiO_2-ZrO_2型SCR脱硝催化剂,对催化剂进行了XRD表征,并考察了复合载体的组成、WO_3质量分数和高温焙烧处理对催化剂脱硝性能的影响.结果表明:WO_3/TiO_2-ZrO_2催化剂具有很好的热稳定性,经800℃高温处理后晶相结构保持不变且脱硝效率仅有微弱下降;WO_3质量分数为20%、钛锆比为7∶3和0∶10的2种催化剂具有较好的脱硝性能,能够适用于高温脱硝反应.     

Ni_(0.8)Fe_(0.2)Cu_m(PrZr_4)_nO_x催化剂的制备及其乙醇水蒸气重整性能研究

用共沉淀法制备Pr Zr4Oy载体,浸渍法制备Ni0.8Fe0.2Cum(Pr Zr4)nOx系列催化剂,并将其用于乙醇水蒸气重整反应(ESR),考察Cu的掺杂量对催化剂性能的影响。通过X射线粉末衍射(XRD)、程序升温还原(TPR)和扫描电子显微镜(SEM)对催化剂的晶体结构、还原特性和表面形态进行表征,结果显示,新鲜催化剂中存在立方晶相Pr6O11、立方晶相Pr2Zr2O7、斜六方晶相Pr Ni O3,在Cu含量较高的催化剂上还出现了单斜晶相Cu O。催化剂经过550℃还原预处理后,Ni、Cu组分均以零价态存在,Fe组分被部分还原为Fe3O4的形式;掺杂Cu组分可提高Ni3+和Fe3+的还原活性。Ni0.8Fe0.2Cu0.2Pr Zr4Ox催化剂在乙醇水蒸气重整反应中表现出较好的性能,在500℃的条件下,乙醇转化率接近100%,一氧化碳摩尔分数低至0.15%;在反应进程中未发现催化剂积碳、烧结和失活现象,催化剂稳定性良好。     

不同沉淀条件制备γ-Fe_2O_3催化剂的表征及其NH_3-SCR性能

采用不同沉淀工艺制备磁性γ-Fe2O3催化剂,在固定床上对其NH3-SCR性能进行研究,借助XRD和N2吸附分析揭示了其物性.结果表明,采用正向滴定法、NH4OH作为沉淀剂制得的γ-Fe2O3催化剂纯度高,结晶度适宜,孔径主要分布于2~5,nm,有利于脱硝;实验工况下,325~400,℃温度区间内,其脱硝效率保持90%以上.沉淀剂种类及其加入方法直接影响催化剂的脱硝性能,不当的沉淀工艺会导致α-Fe2O3生成、晶粒直径过大、孔结构塌陷等问题,不利于脱硝.     

TiCe_(0.2)W_(0.2)O_x型SCR催化剂涂覆方法研究

分别运用传统浸渍涂覆、溶液燃烧涂覆、新型浸渍涂覆制备了一系列涂覆有TiCe0.2W0.2Ox活性组分整体式催化剂,比较发现新型浸渍涂覆催化剂SCR性能最好。新型浸渍涂覆的催化剂在250~450℃温度范围NO去除率超过90%,N2选择性在450℃以内都大于99%。对NOx转化率、N2选择性及各种表征结果进行分析显示新型浸渍涂覆的催化剂催化活性与涂覆量成正比关系,比表面积越大,催化活性越好,催化活性与催化剂粉末粒径无明显对应关系。     

浅析不同因素对商用Al2O3负载型催化剂的影响

在固定床脱硝试验装置上,考察催化剂数量、反应温度、SO2浓度等反应条件对某小型商用Al2O3负载型催化剂催化性能的影响.结果表明,催化剂个数为6时,催化活性最佳;反应温度在360℃～420℃范围内,催化剂活性较高,NOx去除率高于60％;SO2浓度的变化对催化剂活性有较大影响,且高浓度SO2对催化剂活性存在明显抑制作用...     

TiO_2粉末体系光电化学生成氨(NH_4~ )的研究

用载有助催化剂的粉末TiO_2作为催化剂,气-固-液三相在反应过程中共存的体系,通过光照将N_2还原得到了氨(用酸性电解液的情况呈NH_4~ 态,下文同此)。研究了催化剂量、光照时间以及载某些金属(特别是稀土元素)氧化物对氨产率的影响。     

O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2)正极Na^(+)传输动力学及相变机制北大核心CSCD

钠离子电池因其成本低廉、环境友好且与锂离子电池工作原理相似,在大规模储能领域极具应用潜力。作为决定电池能量密度的关键组成部分,O3型钠基层状过渡金属氧化物因高容量、合成简单等优势在众多正极材料中脱颖而出。然而,Na^(+)在O3结构中八面体位点间的迁移需克服较大的能垒,最终导致复杂反应相变的发生和容量快速衰减。因此,探究O3型正极材料电化学反应过程中Na^(+)脱嵌行为与结构演变的构效关系对开发高性能正极材料至关重要。本工作以O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2)(O3-NFM)正极为研究对象,对其电化学性能、Na^(+)传输动力学性质及相变机制展开了系统研究。电化学测试结果表明,O3-NFM在充电至高压(4.3 V)时可脱出0.84 mol Na^(+),发挥约201.9 mAh/g的比容量,但可逆性欠佳。当截止电压为4.0 V时,该正极材料循环性能优异,原位XRD结果进一步证明了电化学反应过程中O3-P3/O3-P3-P3/O3-O3的可逆结构转变。循环伏安(CV)曲线和恒电流间歇滴定技术(GITT)结果表明其具有快速的钠离子扩散速率,从而表现出较好的倍率性能。本研究为探索以O3-NFM为基础的正极材料结构设计及性能调控提供了理论基础。     

含硫钾盐对V_2O_5-WO_3/TiO_2催化剂上SO_3生成特性的影响

采用湿式浸渍法制备含硫钾盐催化剂,研究含硫钾盐对SCR催化剂上SO_3生成特性的影响,并采用不同分析技术对SCR催化剂特性进行表征。结果表明:K_2S_2O_7和K_2SO_4能明显提高SO_3生成率;随着含硫钾盐质量分数的增加,SO_3生成率提高;在410℃下3.6%K_2S_2O_7-SCR催化剂的SO_3生成率达到最大;SO_2质量浓度为3 000 mg/m~3时,3.6%K_2S_2O_7-SCR催化剂的SO_3质量浓度最大;含硫钾盐存在时,SCR催化剂的还原性能下降,比表面积减小;含硫钾盐存在时,SCR催化剂表面化学吸附氧质量分数和V~(5+)质量分数均增大,V~(5+)=O键的振动峰强度明显增强,SCR催化剂的氧化能力增强。     

PdO/ZrO2 engineered (La0.8Sr0.2)0.95MnO3-δ-(Y2O3)0.08(ZrO2)0.92 cathode for use in intermediate temperature solid oxide fuel cells

To enhance the electrochemical performance of (La_0.8Sr_0.2)_0.95MnO_3-δ-8 mol. % Y₂O₃ stabilized ZrO₂ (LSM-YSZ) cathode at reduced temperatures, PdO and ZrO₂ (Pd/Zr = 0.8/0.2) are co-infiltrated into the LSM-YSZ scaffold. Such prepared composite cathode is investigated at temperatures between 600 and 750 °C and cathodic current densities of 400 and 800 mA cm^?2. It is observed that PdO particles are uniformly deposited on the surface of the LSM-YSZ and surrounded by nano-sized ZrO₂ particles. This distinctive microstructure possesses improved thermal stability under current at 750 °C due to the hindering effect of ZrO₂ on the agglomeration and growth of PdO particles. As a result, the electrocatalytic activity of the cathode for oxygen reduction reaction (ORR) is greatly enhanced due to presence of the self-limited PdO particles. At open circuit voltage, the initial polarization resistance decreases from 1.68 to 0.40 Ω cm² as temperature increases from 600 to 750 °C; and the polarization resistance is fully stabilized at the level of 0.36 and 0.34 Ω cm², respectively, after current polarization at 750 °C under 400 and 800 mA cm^?2 for less than 200 h.     

B_(2)O_(3)包覆NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)正极材料制备及其电化学性能北大核心CSCD

O3型层状氧化物正极材料NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)具有高比容量、低成本和环境友好性等优点,被认为是最有前途的钠离子电池正极材料之一,但在充放电过程中会发生一系列复杂的相变,导致电化学性能较差。本研究报道了一种协同改性方法,以同时提高NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料的循环稳定性和倍率性能。通过将硼酸粉末和正极材料固相球磨混匀后低温煅烧,在NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料表面包覆纳米非金属氧化物B_(2)O_(3)。借助X射线衍射仪(XRD)、扫描电子显微技术(SEM)、透射电子显微镜(TEM)和电化学技术等测试手段,对比分析不同包覆量和原材料的形貌和电化学性能,筛选得到最优包覆量为2%(质量分数,余同)。该方法实现了B_(2)O_(3)的均匀包覆,并且没有改变NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料的晶体结构。通过电化学性能测试表明2%B_(2)O_(3)包覆材料在1 C倍率下循环200圈容量保持率从78%提升至87%。同时,2%B_(2)O_(3)包覆材料的高倍率性能也得到了改善,10 C高倍率下放电比容量从75 mAh/g提升至99 mAh/g。结果表明,这是一种有效且可靠的表面改性策略,可以增强钠离子电池层状氧化物正极材料的电化学性能。     

过渡金属氧化物(MnO_x-CeO_2)改性铜基催化剂的低温SCR脱硝性能研究

利用溶胶凝胶法,将过渡金属氧化物(MnO_x-CeO_2)掺杂到铜基催化剂CuO/γ-Al_2O_3上,制备了不同配比的CuO-MnO_x-CeO_2/γ-Al_2O_3催化剂颗粒,采用程序升温方法在催化反应效能评价系统里测试了其在模拟烟气条件下的低温SCR脱硝性能。利用比表面积测试仪(BET)、X射线衍射仪(XRD)和扫描电子显微镜(SEM)对催化剂进行表征分析,分析了MnO_x-CeO_2改性铜基催化剂低温SCR脱硝的反应机理。结果表明:6%CuO-5%MnO_x-10%CeO_2/γ-Al2O3的催化剂颗粒在100~200℃内的脱硝效率保持在80%以上;SO_2和H_2O对SCR脱硝反应均有抑制作用;O_2是SCR反应持续进行的必要条件。     

Alternative production route for supporting La0.8Sr0.2MnO3−δ-Ce0.8Gd0.2O2−δ (LSM-GDC)

Tape casting is a widely used ceramic process that generally makes use of pore former agents to produce elements with engineered porosity for SOFC applications. In this work, porous La_0.8Sr_0.2MnO_3−δ-Ce_0.8Gd_0.2O_2−δ (LSM-GDC) supporting cathode of suitable porosity was produced using the reactive sintering approach without using of pore forming agent. The reactive sintering approach was considered in order to exploit the porosity induced by the precursor decomposition during a single thermal treatment of calcining-debonding-sintering. A stable tape casting slurry of lanthanum, strontium and manganite precursors and GDC powder was used in order to obtain large-area, crack-free green tapes. This process allowed to obtain 10 × 10 cm² LSM-GDC sintered tapes of thickness 600 μm with values of porosity and mechanical strength suitable for fuel cells applications, starting from the precursor mixture without the addition of pore former and avoiding any calcination step. Preliminary results show that the same conditions can be used to produce a LSM-GDC/GDC half-cell by co-firing this tape with on the top a screen-printed GDC layer. To the author knowledge this is the first time that the reactive sintering approach has been used to produce a large-area supporting cathode suitable for SOFC applications.     

Hydrogen sorption properties of LixNa1−xMgH3 (x = 0, 0.2, 0.5 & 0.8)

The synthesis, thermodynamic destabilisation and hydrogen absorption/desorption characteristics of the Li_xNa_1?xMgH₃ system with (x = 0, 0.2, 0.5 and 0.8 M ratios) have been investigated. Samples were mechanically milled under argon for 5 h; then characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Diffraction peaks of NaMgH₃ phase shifted to higher angles and lattice parameters decreased due to the Li addition into the system. 2 and 3 endothermic reactions were observed for the Li_x substituted samples (x = 0, 0.2, 0.5, 0.8). Li_0.8Na_0.2MgH₃ hydride showed the best performance among the other quaternary hydrides (synthesised in this work) releasing 5.2 wt.% of H₂ at 314 °C. Rehydrogenation of the decomposed Li_xNa_1?xMgH₃ (x = 0, 0.2, 0.5 & 0.8) samples was experimentally confirmed under 10 bar H₂ at ～250 °C.     

Study of BaCe0.4Zr0.4Y0.2O3-δ/BaCe0.8Pr0.2O3-δ (BCZY/BCP) bilayer membrane for Protonic Conductor Solid Oxide Fuel Cells (PC-SOFC)

This paper address the blocking of the electronic conductivity for a BaCe_0.8Pr_0.2O_3-δ (BCP) material due to the addition of a BaCe_0.4Zr_0.4Y_0.2O_3-δ (BCZY) thin layer. Barium cerates (BCP and BCZY) show interesting features as electrolytes for Proton Conducting Solid Oxide Fuel Cells (PC-SOFC). BCP perovskite displays good mechanical properties associated to its sintering capability, typically proposed as a possible electrolyte. However, this compound shows poor CO₂ tolerance above 500 °C and presents mixed conductivity under wet synthetic air. Protonic transport is the main feature of BCZY perovskite and it presents an excellent CO₂ tolerance. However, the drawback of this compound is its high grain boundary resistance. In this work, a BCZY film was grown by Pulsed Laser Deposition (PLD) on BCP in order to block its electronic conductivity and improve CO₂ tolerance. From the electrochemical characterization of materials, it is proposed that BCP dominates transport mechanisms on the BCZY/BCP bilayer membranes under wet synthetic air and wet diluted hydrogen. Our measurements confirm that the BCZY film blocks the electronic conductivity of BCP under wet synthetic air and protects it from CO₂-containig atmospheres. Due to this set of properties, the BCZY/BCP bilayer membrane represents a possible candidate as electrolyte for PC-SOFC operating between 400 and 600 °C.     

An ionic conductor Ce0.8Sm0.2O2−δ (SDC) and semiconductor Sm0.5Sr0.5CoO3 (SSC) composite for high performance electrolyte-free fuel cell

An advanced electrolyte-free fuel cell (EFFC) was developed. In the EFFC, a composite layer made from a mixture of ionic conductor (Ce_0.8Sm_0.2O_2?δ, SDC) and semiconductor (Sm_0.5Sr_0.5CoO₃, SSC) was adopted to replace the electrolyte layer. The crystal structure, morphology and electrical properties of the composite were characterized by X-ray diffraction analysis (XRD), scanning electron microscope (SEM), and electrochemical impedance spectrum (EIS). Various ratios of SDC to SSC in the composite were modulated to achieve balanced ionic and electronic conductivities and good fuel cell performances. Fuel cell with an optimum ratio of 3SDC:2SSC (wt.%) reached the maximum power density of 741 mW cm^?2 at 550 °C. The results have illuminated that the SDC-SCC layer, similar to a conventional cathode, can replace the electrolyte to make the EFFC functions when the ionic and electronic conductivities were balanced.     

Stability considerations of semiconductor ionic fuel cells from a LNCA (LiNi0.8Co0.15Al0.05O2-δ) and Sm-doped ceria (SDC; Ce0.8Sm0.2O2-δ) composite electrolyte

Recent advances in composite materials, especially semiconductor materials incorporating ionic conductor materials, have led to significant improvements in the performance of low-temperature fuel cells. In this paper, we present a semiconductor LNCA (LiNi_0.8Co_0.15Al_0.05O_2-δ) which is often used as electrode material and ionic Sm-doped ceria (SDC; Ce_0.8Sm_0.2O_2-δ) composite electrolyte, sandwiched between LNCA thin-layer electrodes in a configuration of Ni-LNCA/SDC-LNCA/LNCA-Ni. The incorporation of the semiconductor LNCA into the SDC electrolyte with optimized weight ratios resulted in a significant power improvement, from 345 mW cm^?2 with a pure SDC electrolyte to 995 mW cm^?2 with the ionic-semiconductor SDC-LNCA one where the corresponding ionic conductivity reaches 0.255 S cm^?1 at 550 °C. Interestingly, the coexistence of ionic and electron conduction in the SDC-LNCA membrane displayed not any electronic short-circuiting but enhanced the device power outputs. This study demonstrates a new fuel cell working principle and simplifies technologies of applying functional ionic-semiconductor membranes and symmetrical electrodes to replace conventional electrolyte and electrochemical technologies for a new generation of fuel cells, different from the conventional complex anode, electrolyte, and cathode configuration.     

在以TiO_2为基质的催化剂上Cr_2O_7~(2-)离子光催化还原活性的研究

半导体粉末悬浮体系的光化学反应的研究是从五十年代开始的。近年来,从太阳能利用出发,光催化反应的研究得到了更大的重视。随着太阳能光化学研究的进展,光催化法处理废水的研究也引起了国内外的注意。 1977年,Miyake等首先报道了悬浮着TiO_2粉末的含Cr_2O_7~(2-)离子的水溶液,光照时     

High-performance La0.5(Ba0.75Ca0.25)0.5Co0.8Fe0.2O3-δ cathode for proton-conducting solid oxide fuel cells

La_0.5(Ba_0.75Ca_0.25)_0.5Co_0.8Fe_0.2O_3-δ, a simple perovskite cathode material with high electrical conductivity (940 S cm^?1 at 600 °C) and impressive surface catalytic activity, was prepared and used in proton-conducting solid oxide fuel cells. As its thermal expansion coefficient is higher than that of the electrolyte material BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ, they were combined and used as a composite cathode. The crystal structure, chemical compatibility, electrical conductivity, cell performance, and the oxygen reduction reaction of the cathode material were explored, and we found that the single fuel cell developed with the composite cathode achieved excellent electrochemical performance, with both a low polarization resistance and high peak power density (0.044 Ω cm² and 1102 mW cm^?2 at 750 °C, respectively). Outstanding stability was also achieved, as indicated by a long-term 100-h test. Additionally, the rate-limiting steps of the oxygen reduction reaction were the oxygen adsorption, dissociation, and diffusion processes.     

Long-term stability of Pt/Ce0.8Me0.2O2-γ/Al2O3 (Me = Gd,Nb, Pr,and Zr) catalysts for steam reforming of methane

This study investigated the influence of dopants (Gd, Nb, Pr, and Zr) on the performance of Pt/Ce_xMe_1-xO_2-γ/Al₂O₃ catalysts for the methane steam reforming (SRM) at 1073 K and at different space velocities. In-situ XRD, in-situ XANES, and Raman spectroscopy revealed the formation of a solid solution on the supports with Gd, Pr and Zr and an improvement in reducibility. No evidence of complete niobium inclusion into the ceria framework was observed and AlNbO₄ and CeNbO₄ phases were detected. All catalysts exhibited a severe initial deactivation, however, with Pt/CeNb/Al being most stable. Analyses of all spent catalysts revealed a negligible carbon deposition during the catalytic tests. TEM, XRD and N₂ physisorption showed a collapse of the alumina structure and sintering of Pt particles as causing the early deactivation. The formation of segregated phases for Nb-doped ceria improved the thermal resistance of alumina and provided a closer contact with Pt crystallites, resulting in better stability.