Novel MnO x Catalysts for NO Reduction at Low Temperature with Ammonia

Novel MnO_x catalysts for NO reduction at low temperature with NH₃ have been prepared by a simple precipitation method using sodium carbonate. The catalysts thus obtained have exhibited excellent catalytic activity in the temperature range of 348–473 K compared with other MnO_x-based catalysts, which is probably due to its high surface area as well as framework structure and composition. The high catalytic activity is maintained in the presence of 20 vol% water vapor in the feed.     

Cu、Co掺杂Mn基复合金属氧化物的低温NO_x储存还原性能

采用共沉淀法制备了掺杂铜或钴的锰基复合金属氧化物催化剂,考察了其稀燃条件下的NOx储存活性以及稀燃/富燃气氛中的NOx储存还原(NSR)性能。结果表明,Mn-O样品在200℃具有较好的NOx储存活性,NO-to-NO2转化率为83.4%,氮氧化物储存量(NSC)为124.2μmol/g;但其在富燃气氛中的NOx还原能力较低。掺杂少量铜或钴元素之后,样品的晶粒尺寸变小,抗烧结能力增强,同时BET比表面积增大,低温下NOx储存和还原活性均有所提高。通过H2-TPR表征发现:掺杂少量铜或钴元素之后,H2还原峰向低温方向偏移,氧物种的活性有所提高,这有助于提高催化剂的氧化还原能力;其中掺杂铜样品的氧化还原能力最强,在富燃条件下表现较高的NSR活性。     

Differences Between Al2O3 and Ag/Al2O3 for Lean Reduction of NO x with Dimethyl Ether

Lean reduction of NO _x with DME occurs with high selectivity to N₂ over Al₂O₃ between 300 °C and 550 °C with a maximum of 47% at 380 °C, and with lower selectivity over Ag/Al₂O₃ between 250 °C and 400 °C due to the catalysts’ sensitivity to gas phase radical reactions and activity for NO _x reduction with methanol.     

低温合成MgO-Al_2O_3-FeO_n复相材料

高铁镁砂中分别引入质量分数为3%、6%、9%、12%、15%的板状刚玉,经1 420℃烧结制备Mg O-Al2O3-Fe On复相材料。采用X射线衍射和扫描电子显微镜分析试样的物相组成及显微结构。结果表明:在1 420℃,高铁镁砂与板状刚玉反应烧结形成原位合成的镁铁铝尖晶石固溶体,铁氧化物的存在促进了镁铁铝尖晶石固溶体的形成。随着板状刚玉加入量的增加,镁铁铝尖晶石固溶体的含量随之增加。镁铁铝尖晶石固溶体呈现明显的环带结构。最外层环带结构致密,富含铁氧化物;次外层环带结构中铁氧化物的含量有所降低。这些环带结构使得低温制备镁铁铝尖晶石固溶体结合方镁石材料的新工艺得以实现。     

The NO x reduction mechanism by H2 under near isothermal conditions over Pt–Ba/Al2O3 Lean NO x Trap systems

The study of the gas-phase NO reduction by H₂ and of the stability/reactivity of NO _x stored over Pt–Ba/Al₂O₃ Lean NO _x Trap systems allowed to propose the occurrence of a reduction process of the stored nitrates occurring via to a Pt-catalyzed surface reaction which does not involve, as a preliminary step, the thermal decomposition of the adsorbed NO _x species.     

新型CuSO4-CeO2/TS催化剂低温NH3还原NO及抗中毒性能

采用共沉淀法制备了载体TiO2-SiO2(TS),用浸渍法制备了CuSO4-CeO2/TS催化剂,研究了制备参数和操作条件对其低温NH3选择性催化还原NO性能的影响及其抗H2O和SO2中毒的能力. 结果表明,在最佳条件下制得的CuSO4-CeO2/TS,在反应温度220℃、NH3/NO摩尔比为1.1、进口NO浓度1000′10-6(j)、空速5000 h-1及O2 4%(j)条件下,NO转化率接近98%. 本催化剂低温下具有良好的单独抗水、硫的能力,且在长达33 h同时抗H2O和SO2的过程中,其活性保持在约95%的高水平,没有中毒迹象,在综合性能上优于目前文献报道的其他SCR催化剂.     

A Study on the Properties and Mechanisms for NO x Storage Over Pt/BaAl2O4-Al2O3 Catalyst

The NO_x storage catalyst Pt/BaAl₂O₄-Al₂O₃ was prepared by a coprecipitation--impregnation method. For fresh sample, the barium mainly exists as the BaAl₂O₄ phase except for some BaCO₃ phase. The BaAl₂O₄ phase is the primary NO _x storage phase of the sample. EXAFS and TPD were used for investigating the mechanism of NO _x storage. It is found that two kinds of Pt sites are likely to operate. Site 1 is responsible for NO chemisorption and site 2 for oxidizing NO to nitrates and nitrites. When NO adsorbs on the sample below 200 °C, it mainly chemisorbs in the form of molecular states. Such adsorption results in an increase of the coordination magnitude of Pt-O, and a decrease of that of Pt-Pt and Pt-Cl. The coordination distance of Pt-Pt, Pt-Cl and Pt-O also increases. When the adsorption occurs above 200 °C, NO can be easily oxidized by O₂, and stored as nitrites or nitrates at the basic BaAl₂O₄. Site 2 is regenerated quickly. A high adsorption temperature is favorable for nitrate formation.     

Nd:Y2O3 Powder Synthesized by Low Temperature Calcination for Fabricating Transparent Ceramics

A precursor for Nd³⁺-doped Y₂O₃ powder was prepared by a coprecipitation method with (NH₄)HCO₃ as precipitant. The influence of fixed duration calcination at low temperature on the micromorphology of the powder, and the subsequent effect of sintering conditions on the transmittance of the resulting Nd³⁺-doped Y₂O₃ ceramic was systematically studied. The results show that the shape of the Y₂O₃ particles changes from acicular to flake-like by calcining for 2 h and increasing the calcination temperature, and that a sample sintered at 1983 K for 8 h after being calcined at 973 K for 2 h shows the highest transmittance. This example of transparent Nd³⁺-doped ceramic is a good candidate for solid-state lasers, IR windows, lamp envelopes, etc.     

CuO和B2O3复合掺杂对BaTi2O5陶瓷的降温烧结与电性能研究

采用非均相共沉淀法制备Ba Ti2O5粉体,以固相烧结法制备了Cu O和B2O3复合掺杂的Ba Ti2O5陶瓷,并对样品进行了XRD、SEM表征和电性能测试。结果表明:掺杂后制得的Ba Ti2O5陶瓷在1100℃烧结2 h的致密度达到96.71%,晶粒发育较完整,在室温下具有良好的铁电滞后特征,在测试频率1 KHz时,Ba Ti2O5陶瓷的介电常数为εr=71.96,说明在烧结过程中加入复合烧结助剂Cu O和B2O3可以促进液相形成并减少了气孔率,从而提高了陶瓷的致密度和介电性能。     

掺杂ZnO-B2O3低温烧结BiNbO4介质陶瓷的研究

研究了烧结助剂ZnO-B2O3对BiNbO4陶瓷烧结特性及介电性能的影响.结果表明ZnO-B2O3形成晶界玻璃相存在于晶粒之间,促进烧结,大幅度降低BiNbO4陶瓷的烧结温度,促使瓷体晶粒尺寸均匀和致密;但ZB的质量分数大于3%,阻碍晶粒长大,破坏晶体结构和排列,导致材料的缺陷和本征损耗增加,从而降低材料的介电性能.ZnO-B2O3的掺杂量以1%为最佳,在880℃保温4h,可达到97%理论密度,在100MHz测试频率下,εr=42,tanδ＜1.5×10-3.     

Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NO x Storage Catalyst

In this paper we propose an effective global kinetic model that allows prediction of N₂O and NH₃ formation during the reduction of stored NO _x in dependence on the composition of the rich mixture (H₂/CO/C₃H₆), actual operating temperature, and length of regeneration period. A bench flow reactor equipped with a high-speed FTIR was used to measure dynamic evolution of gas components during periodic lean/rich operation of a fully formulated NSRC catalyst (PtPdRh/Ba/Ce–Zr/Mg–Al/Al₂O₃).     

SiO2-B2O3-Al2O3-CaO-ZnO-KNaO-F2系统无铅低温透明釉的研制

以B2O3 、CaO、ZnO、KNaO、CaF2为熔剂制备在1120℃左右烧成的无铅透明釉.探究了釉组成中CaO、CaF2、B2O3、Al2O3含量对釉面光泽度、透明度等的影响.结果表明,提高釉中CaO、A12O3含量可以抑制分相,提高釉的透明度,但会产生气泡降低釉的光泽度,用适量CaF2取代CaO可以解决这个问题.制备的透明釉釉面光泽度达102.9,釉面显微硬度、热稳定性能够达到日用陶瓷的标准要求.     

Y2O3掺杂稳定ZrO2配合物的前驱体分子结构及小尺寸效应

利用密度泛函理论中的B3LYP方法,计算了前驱体溶液中可能的锆和钇生长基元及相应的浓缩长大配合产物的结构。深入探讨了氧化锆前驱体溶胶中分子的结构、原子的Mulliken电荷布局和晶粒生长机制。理论结果表明掺杂引起粒径尺寸减少是由于掺杂引起氧桥聚合速度减慢和颗粒间吸引力的减弱。     

Y2O3和MgO部分稳定ZrO2陶瓷热稳定性和低温烧结研究

本文研究了Ｙ２Ｏ３，ＭｇＯ含量对Ｙ，Ｍｇ－ＰＳＺ材料性能的影响，发现由于Ｙ２Ｏ３的加入，ＭｇＯ含量的提高可使Ｍｇ－ＰＳＺ的烧成温度由原来的１７００℃降低到１６００℃，与此同时材料的热稳定性也得到了较大的改善。     

氧化铝陶瓷的低温烧结技术

本文从原料细度、化学组成以及烧成工艺三方面对氧化铝陶瓷烧结温度的影响进行了概述，简要介绍了几种降低氧化铝陶瓷烧结温度的实用工艺与方法。     

Effect of Low Concentration of SO x on NO Reduction with Propene Over Ag/Al2O3

Catalytic activity for NO reduction with propene was investigated at 0–80 ppm SO₂. NO was reduced more efficiently by propene on SO₂-treated than untreated catalyst. Simultaneously, combustion of reductant was observed to lower NO reduction efficiency. Thus, the role of surface-adsorbed SO _x species was regarded as depressing reductant combustion. NH₃ adsorption revealed that SO₂ treatment increased Bronsted acidity of the Ag/Al₂O₃ catalyst, which promoted propene activation. Reductant activation is a more important step, compared with NO activation to oxidative nitrate species. The NCO species, an index intermediate in NO _x reduction, was produced on SO₂-adsorbed Ag/Al₂O₃ at a lower temperature (473 K) than on the untreated catalyst. The reductive intermediates at low temperature are suggested to be alcohol, or aldehyde-adsorbed species, based on observed C=O band.     

A Novel Glass Membrane for Low Temperature H2/O2 Fuel Cell Electrolytes

A novel structure for an H₂/O₂ fuel cell with a proton conducting glass electrolyte and a Pt/C catalyst was developed. The performance of the fuel cell, which was impregnated with a glass electrolyte and a gaseous hydrogen–oxygen feed at low temperature in a humidified atmosphere was significantly improved by introducing membrane electrode assemblies (MEAs) consisting of heteropolyacids (HPAs) (phosphotungstic acid, PWA and phosphomolybdic acid, PMA) doped with a P₂O₅‐SiO₂ glass electrolyte. The HPAs containing porous glass electrolytes show promise for applications in low temperature H₂/O₂ fuel cells. The electrochemical behaviour of these materials was studied by measuring the current–voltage profile from polarisation curves. A maximum power density of ≈ 35 mW cm^–2 was obtained at 30 °C and 30% RH (relative humidity) using a PMA/PWA‐P₂O₅‐SiO₂ glass electrolyte membrane. The impedance measurements displaying the total cell ohmic resistance for 12 h at 0.5 V were evaluated at 30 °C. The resistance value was 3.5 Ω for an operating time of 12 h. This MEA showed the best and the most stable performance for use in an H₂/O₂ fuel cell.     

Novel Temperature Stable Li2MnO3 Dielectric Ceramics with High Q for LTCC Applications

Novel microwave dielectric ceramics in the Li₂MnO₃ system with high Q prepared through a conventional solid‐state route had been investigated. All the specimens exhibited single phase ceramics sintered in the temperature range 1140°C–1230°C. The microwave dielectric properties of Li₂MnO₃ ceramics were strongly correlated with sintering temperature and density. The best microwave dielectric properties of ε_r = 13.6, Q × f = 97 000 (GHz), and τ_f = ?5.2 ppm/°C could be obtained as sintered at 1200°C for 4 h. BaCu(B₂O₅) (BCB) could effectively lower the sintering temperature from 1200°C to 930°C and slightly induced degradation of the microwave dielectric properties. The Li₂MnO₃ ceramics doped with 2 wt% BaCu(B₂O₅) had excellent dielectric properties of ε_r = 11.9, Q × f = 80 600 (GHz), and τ_f = 0 ppm/°C. With low sintering temperature and good dielectric properties, the BCB added Li₂MnO₃ ceramics are suitable candidates for LTCC applications in wireless communication system.     

Gd2O3和Y2O3共掺CeO2基中温SOFC电解质材料的合成

采用固相合成法合成Gd2O3和Y2O3共掺CeO2基粉料[(CeO2)0.92(Y2O3)0.08-x(Gd2O3)x,x=0,0.02,0.04,0.06,0.08,摩尔分数,下同],在1 600 ℃烧成制备固态氧化物燃料池(solid oxide fuel cells,SOFC)电解材料.采用X射线衍射仪、热膨胀测...     

溶胶-凝胶法制备ZnO-B2O3-SiO2系低温玻璃料

以Zn(CH3COO)1·2H2O、Si(OC2H5)4、H3BO3为原料,采用溶胶-凝胶法首先制备出ZnO-B2O3-SiO2凝胶,再经一定的热处理制度对凝胶进行热处理,制备出ZnO-B2 O3-SiO2微晶玻璃料.通过TG-DSC、FTIR、XRD现代测试手段对干凝胶以及热处理产物进行了表征.结果表明:干凝胶在684℃时可析出晶粒,在730℃温度下已经能够形成稳定的Zn2SiO4和少量鳞石英SiO2晶相,晶粒尺寸细小为39.0 nm,随着热处理温度的升高,析出品相种类没有变化,晶粒粒径明显的增大.