焙烧温度对Cu-Mn/γ-Al2O3催化剂催化氧化甲苯性能的影响

采用浸渍法合成了Cu-Mn/γ-Al₂O₃催化剂, 通过XRD、BET、H₂-TPR和XPS等方法对经不同温度(300~600℃)焙烧的催化剂进行表征, 采用固定床管式反应装置考察了焙烧温度对催化剂催化氧化甲苯的影响, 并讨论活性组分、表面Cu⁺/(Cu⁺+Cu²⁺)和Mn⁴⁺/(Mn⁴⁺+Mn³⁺)摩尔比值与催化剂活性的关系。结果发现, 550℃焙烧温度的催化剂活性最好, 氧化能力最强, 其转化率为95%时对应的反应温度T₉₅(286 ℃)最低, CO₂的选择性达100%。在550℃焙烧时生成的Cu_1.4Mn_1.6O₄新相以及催化剂表面中相对含量更高的Cu⁺和Mn⁴⁺是催化剂具有高活性的主要原因。     

尖晶石型AFe2O4催化剂的制备及其催化燃烧甲苯的研究

通过溶胶-凝胶-自蔓延燃烧法制备尖晶石型AFe₂O₄(A=Cu, Co, Ni, Mg, Zn)催化剂, 以甲苯为VOCs模拟气, 考察AFe₂O₄催化剂对VOCs的催化燃烧活性, 并采用XRD、N₂吸附-脱附、SEM、TEM、H₂-TPR、XPS对催化剂进行表征分析。结果表明: AFe₂O₄表现出较好的催化燃烧活性, 其中CuFe₂O₄的催化燃烧活性最佳, 起燃温度(T50)和完全燃烧温度(T90)分别为188℃、239℃。AFe₂O₄具有明显的片状尖晶石晶体, 并形成以介孔为主的多级孔结构, 该特点为催化剂提供了大量表面活性位。A位元素种类对其催化燃烧活性影响较大, 当A位元素为Cu时, Cu的H₂还原峰面积远大于其他元素, H₂还原温度仅为289℃, 表面亲电子氧和氧空位浓度占氧元素总量(O_ele/O_1S)的36%。CuFe₂O₄为片状反尖晶石晶型, 晶格体积仅为0.294 nm³, 并伴有CuO和α-Fe₂O₃物种。以介孔为主的多级孔结构、特有的片状反尖晶石晶型以及该晶型与CuO和α-Fe₂O₃的协同作用是CuFe₂O₄催化燃烧活性提高的主要原因。     

CeO2修饰Mn-Fe-O复合材料及其NH3-SCR脱硝催化性能

氨选择性催化还原(NH3-SCR)技术需要进一步研发在相对较低温度(<300℃)下具有良好催化活性、高稳定性及环境友好的脱硝催化材料。本工作采用草酸共沉淀法制备Mn-Fe-O催化材料,并对其进行不同含量CeO2修饰,用于低温NH3-SCR脱硝催化反应。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、氮气吸附-脱附、X射线光电子能谱(XPS)、程序升温还原或脱附(H2-TPR、NH3-TPD)等手段对催化剂进行了表征。催化结果表明,在相同反应条件下适量CeO2修饰后的Mn-Fe-O样品比纯Mn-Fe-O表现出更优异的NH3-SCR脱硝催化性能,在80℃时NO转化率在95%以上,且具有较高的N2选择性。CeO2修饰提高了Mn-Fe-O氧化物表面的Fe^3+、Mn^3+和Mn4+含量及表面酸性位点数量,从而有助于NH3的吸附及催化反应的进行,并且Fe^2+/Fe^3+、Mn^2+/Mn^3+/Mn^4+以及Ce^3+/Ce^4+电子对之间的相互氧化还原反应提高了催化剂的氧化还原能力及稳定性。     

陈化体系中醇对Ce0.65Zr0.35O2及其负载的单Pd催化剂性能的影响

采用共沉淀法制备了Ce_0.65Zr_0.35O₂(CZ)储氧材料, 分别以乙醇-水、丙醇-水、乙二醇-水、丙三醇-水体系对沉淀物进行陈化, 研究了醇的种类对CZ及其负载的单Pd催化剂性能的影响。对CZ进行了扫描电镜(SEM), N₂-吸脱附分析, 对Pd/CZ进行了粉末X射线衍射(XRD)、X射线光电子能谱(XPS)、储氧量 (OSC)和程序升温还原( H₂-TPR)的表征, 并考察了三效催化性能。结果表明, 醇的种类对CZ及Pd/CZ的性能有显著影响。在乙醇-水和丙醇-水陈化体系中制备的CZ分散性高, 颗粒堆积松散, 比表面积和孔径大, 孔容高, 且具有优异的热稳定性, 其中丙醇-水陈化体系中制备的CZ老化后比表面积和孔容分别可达28 m²/g和0.1 mL/g, 具有最高的热稳定性, 其负载的单Pd催化剂在老化后对C₃H₈、CO和NO转化显著优于乙二醇-水和丙三醇-水陈化体系中制备的CZ所制备的催化剂。     

氧化铈空心球可控合成及其对Pt基催化剂电催化性能的影响

采用水热合成法, 以碳球为模板, 改变焙烧升温速率, 控制影响铈物种的扩散、渗透及碳球结构的收缩率, 制备了单、双壳层CeO₂空心球。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO₂/RGO催化剂, 研究了CeO₂空心球的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、比表面积及孔径分析仪(BET)、扫描电镜(SEM)和电子能谱(EDAX)、透射电镜(TEM)、X射线光电子能谱(XPS)对CeO₂及催化剂的微观结构进行了表征, 利用电化学工作站对催化剂进行电化学性能测试。结果表明: 单、双壳层CeO₂空心球的比表面积为124.44 m²/g、140.95 m²/g, 孔容为0.014427 cm³/(g·nm)、0.018605 cm³/(g·nm), 孔径分布在2~4 nm范围内。催化剂中的CeO₂保持原有的球状形貌, Pt纳米粒子主要分布在CeO₂附近; 当RGO∶CeO₂=1∶2时, 添加了双壳层CeO₂空心球的Pt-CeO₂/RGO催化剂的电催化性能最优, 电化学活性表面积为94.27 m²/g, 对乙醇氧化的峰电流密度值为613.54 A/g, 1000 s的稳态电流密度值为135.45 A/g。     

LaNiO3 modified with Ag nanoparticles as an efficient bifunctional electrocatalyst for rechargeable zinc--air batteries

No-precious bifunctional catalysts with high electrochemical activities and stability were crucial to properties of rechargeable zinc–air batteries. Herein, LaNiO₃ modified with Ag nanoparticles (Ag/LaNiO₃) was prepared by the co-synthesis method and evaluated as the bifunctional oxygen catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with LaNiO₃, Ag/LaNiO₃ demonstrated the enhanced catalytic activity towards ORR/OER as well as higher limited current density and lower onset potential. Moreover, the potential gap between ORR potential (at −3 mA·cm⁻²) and OER potential (at 5 mA·cm⁻²) was 1.16 V. The maximum power density of the primary zinc–air battery with Ag/LaNiO₃ catalyst achieved 60 mW·cm⁻². Furthermore, rechargeable zinc–air batteries operated reversible charge–discharge cycles for 150 cycles without noticeable performance deterioration, which showed its excellent bifunctional activity and cycling stability as oxygen electrocatalyst for rechargeable zinc–air batteries. These results indicated that Ag/LaNiO₃ prepared by the co-synthesis method was a promising bifunctional catalyst for rechargeable zinc–air batteries.     

低负载量Pd/CeO2/γ-Al2O3催化剂用于低温催化氧化VOCs

采用直接吸附法制备了Pd负载量为0.03% (质量分数)的Pd/γ-Al₂O₃和Pd/CeO₂/γ-Al₂O₃催化剂, 并用于评价VOCs的催化氧化性能。通过X射线衍射(XRD)、N₂吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H₂-TPR)等对催化剂的结构和表面性能进行了表征。结果表明, 在VOCs体积分数为0.1%, 空速(GHSV)为18000 mL/(g·h)条件下, Pd/CeO₂/γ-Al₂O₃催化剂上甲苯、丙酮和乙酸乙酯实现98%转化率的温度分别为205、220和275 ℃, 比Pd/γ-Al₂O₃分别降低了15、15和20 ℃, 而且即使在较高的气体空速下, Pd/CeO₂/ γ-Al₂O₃催化剂仍能展现出优异的催化氧化性能, 且具有很好的稳定性和选择性。氧化铈的加入对材料的物理化学性质和催化活性有一定的影响, 其中Pd/CeO₂/γ-Al₂O₃含有Ce ³⁺和高含量的PdO, 活性物种主要以PdO形式均匀地分散在载体γ-Al₂O₃表面。另外, PdO与非化学计量的CeO₂之间的金属-载体相互作用增强了Pd/CeO₂/γ-Al₂O₃催化氧化性能。     

用于高性能单Pd三效催化剂的复合组分CexZr1-xO2材料的制备

用简单的顺序沉淀法制备了两种具有混合组分的CeO₂-ZrO₂材料。用X射线衍射(XRD), 拉曼光谱(Raman), X射线光电子能谱(XPS), 氮气吸附-脱附, 氢气程序升温还原(H₂-TPR)和储氧量(OSC)研究了不同组合形式对负载的单Pd催化剂性能的影响。结果表明, 两个混和组分的催化剂结构和织构性能都得到了改善。由于贵金属和载体材料之间以及载体材料内部各组分之间的强相互作用, 组合的结构促进了Ce³⁺和晶格缺陷的形成, 提高了氧的移动性, 并且相应的催化剂老化前后对于CO、C₃H₈和NO的转化都具有较宽的窗口范围, 说明这种具有混合组分的载体材料在汽油车尾气净化方面具有良好的应用前景。     

FTIR spectroscopy of hydrogen, carbon monoxide, and methane adsorbed and co-adsorbed on zinc oxide

Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H₂/CO, H₂/CH₄ and CO/CH₄ on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn²⁺ ions. Adsorption lowers the CH₄ symmetry from T_d to C_3v, which is reflected in activation of the v₁ (symmetric stretching) mode and discrete frequency shifts of the v₃ (antisymmetric stretching) and ν₄ (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(O–H) band, which originally appear at 1710 and 3492 cm⁻¹, respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas.     

CeO2/石墨烯的合成及其在光催化制氢中的应用

采用具有丰富分级多孔结构的豆芽为模板,经水热法合成仿生形态的纳米CeO₂/石墨烯催化剂。使用XRD、拉曼光谱（Raman）、TEM、场发射扫描电子显微镜（FESEM）、紫外-可见漫反射光谱（UV-Vis/DRS）、N₂吸附-脱附仪和光解水制氢系统等分析表征手段对CeO₂/石墨烯催化剂的结构、形貌及光催化性能进行分析。结果表明,所制备的CeO₂/石墨烯光催化剂不仅继承了豆芽模板高孔隙率和大比表面积的特点,而且保持了豆芽的形态和微观特征。该催化剂是由约5.6 nm CeO₂纳米晶与具有生物形态的仿生石墨烯片层结构结合而成。制得的CeO₂/石墨烯复合材料内部存在大量由CeO₂/石墨烯催化剂纳米颗粒堆积而成的纳米孔,其孔径集中分布于15~45 nm左右,这种微观结构使CeO₂/石墨烯催化剂具有超大的比表面积,提高了催化剂对光生电子空穴对的捕获能力。由紫外-可见漫反射吸收光谱可知,CeO₂/石墨烯复合材料的可见光利用率显著增强,光解水制氢效率6 h后可达到671 μmol（h · g）^-1,远高于标样CeO₂的51.67 μmol（h · g）^-1。     

氧化还原沉淀法制备MnO2/MWCNTs催化剂及其低温SCR活性

先用十二烷基硫酸钠(SDS)对多壁碳纳米管(MWCNTs)进行表面改性, 然后采用氧化还原沉淀法制得一系列的MnO₂/MWCNTs催化剂。考察了催化剂在80~180℃的选择性催化还原(SCR)反应活性, 并通过BET、XRD、FESEM、TEM、XPS和H₂-TPR等表征手段对催化剂的结构及性能进行分析。结果显示, MnO₂/MWCNTs催化剂在空速210 L/(g_cat·h)和温度140~180℃条件下, 脱硝效率达到85%~100%, 这明显优于等体积浸渍法制备的催化剂的低温SCR催化活性, 且10% MnO₂/MWCNTs催化剂的活性最优。分析结果表明, MnO₂/MWCNTs催化剂中MnO₂以纳米片状均匀分散在多壁碳纳米管载体表面; 弱结晶性的结构和高价锰, 较高的表面吸附含氧量及较强的低温区氧化还原能力是10% MnO₂/MWCNTs催化剂具有优异低温SCR活性的原因。另外, 和MnO_x/MWCNTs催化剂相比, 10% MnO₂/MWCNTs催化剂表现出良好的抗水和抗硫性能。     

磁性纳米CeO2/Fe3O4非均相Fenton反应催化降解氧氟沙星

为了提高Fe₃O₄的催化活性, 制备了磁性CeO₂/Fe₃O₄复合纳米粒子, 构成非均相Fenton反应体系, 催化降解水环境中的氧氟沙星抗生素。研究了CeO₂含量、H₂O₂浓度、pH等因素对CeO₂/Fe₃O₄非均相催化活性的影响, 并通过溶出铁离子测定、动力学拟合等方式对反应机理进行探究。结果表明, CeO₂/Fe₃O₄较Fe₃O₄具有更强的催化活性, 氧氟沙星的降解率随CeO₂含量、H₂O₂浓度和溶液酸度的增加而提高, 当H₂O₂浓度为100 mmol/L 以及pH为3时, CeO₂/Fe₃O₄(摩尔比=0.780)-H₂O₂体系催化降解氧氟沙星的效果最佳。CeO₂/Fe₃O₄体系催化降解氧氟沙星反应遵循一级反应动力学方程, 反应机理主要为催化剂表面的催化反应, 同时CeO₂产生氧空位的电子转移对Fe₃O₄的催化反应起到协同强化的作用。     

Enhanced cycle stability of spinel LiMnO by a melting impregnation method

Spinel LiMn₂O₄ particles were successfully coated with CuO, MgO, ZnO, Al₂O₃ and CeO₂ by a melting impregnation method. Except for the CeO₂-coated sample, all the others exhibit better cycling stability than bare LiMn₂O₄ at room temperature and at 55°C. Among these samples, the ZnO-coated sample shows the best cycling stability. A capacity of 100 mA·h·g^-1 still remained after 100 cycles at 55°C while the bare LiMn₂O₄ retains a capacity of only 80 mA·h·g^-1 after the same number of cycles. The improvement in the cycling stability is attributed to the suppressed Mn dissolution caused by HF.     

Ag与Ag2O协同增强TiO2光催化制氢性能的研究

本研究采用两步法制备了电子助剂Ag和界面活性位点Ag₂O共修饰的高效TiO₂光催化剂(TiO₂/Ag-Ag₂O): 首先用光沉积法将Ag负载在TiO₂表面(TiO₂/Ag), 再经过低温煅烧法使部分Ag原位生成Ag₂O。紫外光照射TiO₂时, 激发产生的电子被助剂Ag捕获后快速传输到Ag₂O上, 电子把Ag₂O界面产氢活性位点从溶液中所捕获的氢离子还原成氢气, Ag和Ag₂O的协同作用加快了TiO₂上光生电子的转移和界面产氢反应, 从而提高了TiO₂/Ag-Ag₂O制氢性能。在300 ℃煅烧温度下制备的TiO₂/Ag-Ag₂O光催化剂制氢速率最高, 达到75.20 μmol/h, 分别是TiO₂(3.59 μmol/h)和TiO₂/Ag(41.13 μmol/h)的21.0倍和1.8倍。本研究为光催化制氢材料的设计和制备提供了有益的参考。     

Effect of temperature gradients and stress levels on damage of C/SiC composites in oxidizing atmosphere

Strain response of a C/SiC composite, which is cycled with ΔT₁ of 500 °C at 50 MPa, ΔT₂ of 400 °C at 100 MPa and ΔT₃ of 300 °C at 150 MPa, was investigated. Measured thermo-elastic strain ranges are found to retain 0.209% for ΔT₁, 0.168% for ΔT₂, and 0.122% for ΔT₃, independent upon the applied stress level. Non-linear variations of thermal cycling creep strain can reflect damage evolutions of the composites by changing its rate, which depends on temperature gradient and applied stress. After 104 thermal cycles, strength, modulus, and failure strain of the composites retain 60.29%, 84.2%, and 59% of the initial properties, respectively. The coating cracks of the cycled specimens are observed to be perpendicular to the applied stresses and arranged at relatively regular spacing, through which the fibers are oxidized superficially.     

Ca2+ doping effects in (K,Na, Li)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics

Lead-free (K_0.5−x/2Na_0.5−x/2Li_x)(Nb_0.8Ta_0.2)O₃ (KNLNT) and (K_0.49−x/2Na_0.49−x/2- Li_xCa_0.01)(Nb_0.8Ta_0.2)O₃ (KNLNT-Ca) ceramics were prepared by a conventional ceramic processing. Structural analysis shows that the Ca²⁺ doping takes the A site of ABO₃ perovskite and decreases the phase transition temperature. Property measurements reveal that as a donor dopant, the Ca²⁺ doping results in higher room-temperature dielectric constant, lower dielectric loss, and lower mechanical quality factor. In addition, the Ca²⁺ doping does not change the positive piezoelectric coefficient d₃₃, but increases the converse piezoelectric coefficient d₃₃^* significantly. This is likely due to the increase in the relaxation, as well as the appearance of (Ca_Na/K^•--V_Na/K′) defect dipoles.     

铁助剂对乙酸自热重整制氢用CoxAl3FeyOm±δ催化剂的影响

生物质转化获得的生物质油可作为重要的制氢原料, 选取生物质油的主要成分乙酸作为模型化合物, 开展了乙酸自热重整催化制氢研究。采用共沉淀法制备了铁促进的类水滑石型钴基催化剂, 用于乙酸自热重整制氢体系, 并利用XRD、H₂-TPR、N₂低温物理吸脱附、TG等表征手段对催化剂进行表征测试。结果表明: 通过共沉淀法获得了以类水滑石结构为前驱体的(Co/Fe)_xAl₂CO₃(OH)_y·zH₂O物相; 该前驱体经焙烧后获得的氧化物, 其主要物相为氧化铝担载的尖晶石结构, 包括CoAl₂O₄、Co₃O₄、Fe₃O₄、FeAl₂O₄等, BJH模型计算显示Co_xAl₃Fe_yO_m±δ催化剂形成了介孔结构, 其中Co_0.45Al₃Fe_0.4O_5.55±δ孔径分布集中在4 nm左右, H₂-TPR及XRD测试显示添加助剂Fe提升了催化剂还原度, 并在还原过程中形成了CoFe合金; 所获催化剂在乙酸自热重整反应中, 氢气产率达到 2.72 mol-H₂/mol-HAc, 并保持稳定。表征结果还显示, 该催化剂在反应中结构稳定, CoFe合金稳定存在, 并未出现积炭, 表明催化剂具有抗氧化、抗积碳的特点。     

Catalytic CVD growth and properties of a-C:H and a-C:N

Hydrogenated amorphous carbon (a-C:H) and nitrided amorphous carbon (a-C:N) films have been synthesized on quartz substrates at a substrate temperature of 700 °C using a catalytic chemical vapor deposition (Cat-CVD) method. Raman spectra of a-C:H films showed two principal bands, the G-band at 1600 cm⁻¹ and the D-band at 1350 cm⁻¹. Those of a-C:N films showed similar spectra, with a G′ band at 1640 cm⁻¹, the peak energy of which is higher than that of the G-band in a-C:H. The intensity ratio /I_D, which is a measure of the degree of order in a-C:H, decreased for a-C:H with increasing CH₄/H₂ gas-flow ratio. On the contrary, the /I_D ratio increased with increasing CH₄/H₂ gas-flow ratio.     

Effect of CH4 and H2 on CVD of SiC and TiC for possible fabrication of SiC/TiC/C FGM

SiC and TiC coatings were deposited by CVD on graphite substrates and the effect of the variation of the methane (CH₄) and hydrogen (H₂) ratio on deposition was investigated. SiCl₄, TiCl₄ and CH₄ were used as sources of Si, Ti and C. In case of the SiC coatings, stoichiometric SiC was obtained when the ratios of CH₄/(SiCl₄ + CH₄)andH₂/(SiCl₄ + CH₄) are 0.4 and 10, respectively. Stoichiometric TiC was also obtained under similar conditions. In order to obtain non-stoichiometric materials for possible fabrication of functionally gradient materials (FGM), a change of microstructure and composition was observed with changes of the CH₄ and H₂ ratio. As a result, SiC, TiC and C contents were more easily controlled by a change of the H₂ ratio compared to the CH₄ ratio for SiC and TiC deposition. It has been verified that the change of the H₂ ratio is more desirable for possible manufacturing of SiC/TiC/C FGM.     

Mn-doped perovskite-type oxide LaFeO3 as highly active and durable bifunctional electrocatalysts for oxygen electrode reactions

Perovskite oxides based on the alkaline earth metal lanthanum for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolytes are promising catalysts, but their catalytic activity and stability remain unsatisfactory. Here, we synthesized a series of LaFe_1−xMn_xO₃ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) perovskite oxides by doping Mn into LaFeO₃ (LF). The results show that the doping amount of Mn has a significant effect on the catalytic performance. When x = 0.5, the catalyst LaFe_0.5Mn_0.5O₃ (LFM) exhibits the best performance. The limiting current density in 0.1 mol·L⁻¹ KOH solution is 7 mA·cm⁻², much larger than that of the commercial Pt/C catalyst (5.5 mA·cm⁻²). Meanwhile, the performance of the doped catalyst is also superior to that of commercial Pt/C in terms of the long-term durability. The excellent catalytic performance of LFM may be ascribed to its abundant O²⁻/O⁻ species and low charge transfer resistance after doping the Mn element.