掺杂Fe元素对Pd/C催化剂性能的影响

用Fe作为掺杂元素, 以活性炭为载体, 通过浸渍还原方法制备了Pd:Fe原子比分别为1:1、2:1、1:2的Pd-Fe/C催化剂.采用TEM和XRD技术对合金催化剂的物理性质进行了测试. 结果表明, 获得的Pd-Fe/C催化剂合金粒子在载体上分布均匀, 粒径<5nm,Fe的掺杂量对Pd/C催化剂晶体结构有很大影响, 通过电化学性能测试比较, 分析了三个不同比例的Pd-Fe/C催化剂和Pd/C催化剂对氢和甲酸的电催化氧化性能. 结果得出:在相同的峰值电位下, 几种催化剂的电流密度大小顺序为: Pd-Fe/C(1:1)>Pd-Fe/C(2:1)>Pd/C>Pd-Fe/C(1:2). 结果表明, 适量掺杂Fe提高了Pd/C催化剂的催化性能, 且Pd:Fe原子比为1:1时催化性能最好.     

Pdn-Fe纳米合金作为Mg-H2O2半燃料电池阴极研究

通过化学还原方法制备Pd:Fe原子比(n)为2 : 1、4 : 1、8 : 1的Pd_n-Fe/C催化剂。采用TEM、XRD和XPS技术对复合催化剂进行表征。结果显示, Fe加入Pd/C催化剂中, 与Pd形成合金, Pd_n-Fe/C催化剂的粒径发生变化; 获得的Pd₄-Fe纳米合金粒子在C载体表面分布均匀, 平均粒径为2~3 nm, Fe的加入对Pd/C催化剂晶体结构有很大影响。电化学(CV, LSV, CA)测试表明: 加入Fe提高了Pd/C催化剂的催化性能, Pd/Fe原子比为4 : 1时, Pd_n-Fe/C的催化性能最好。当E=0.2 V时, Pd/C电极电流密度为17.71 mA/cm², 而Pd₄-Fe/C电极电流密度可达19.42 mA/cm²。电池测试表明, 以Pd₄-Fe/C和Pd/C催化剂为阴极的Mg-H₂O₂半燃料电池的开路电势均为1.8 V左右, 而当电流密度为180 mA/cm²时, 以Pd₄-Fe/C为阴极的电池最大能量密度比Pd/C为阴极的电池高41 mW/cm²。     

Cu对Pd/C电催化乙醇氧化性能的影响

以活性碳(Vulcan XC-72)为载体,用改良的化学还原法制备不同Pd:Cu比例的Pd_x-Cu/C催化剂,使用X-射线衍射(XRD)、透射电镜(TEM)、X-射线光电子能谱(XPS)和电化学方法对其进行了表征,研究了Cu对Pd/C催化剂催化性能的影响。结果表明:随着Pd与Cu原子比的提高Pd_x-Cu/C催化剂的催化活性先提高后降低,当Pd:Cu=8:1时Pd8-Cu/C催化剂粒子均匀分散在碳载体表面,其直径约为2.8 nm;在催化剂中掺入的少量Cu元素部分进入Pd晶格形成了合金。这种催化剂在混合水溶液中表现出最佳的催化活性和稳定性,对C_2H_5OH氧化的催化峰电流密度达到114 m A/cm~2,是Pd/C的2.5倍,是JM-Pd/C的3.6倍。     

Pd-X/SnO_2复合催化剂催化乙醇电氧化性能研究

采用溶剂热法制备了SnO_2纳米棒,以其为载体,采用溶剂热还原法制备Pd-X/SnO_2复合催化剂,通过X射线衍射(XRD)、扫描电镜(SEM)及X射线能谱仪(EDS)对复合催化剂进行表征,采用循环伏安法考察了Pd/SnO_2掺杂非贵金属Co、Zn、Fe和Sb复合催化剂对乙醇氧化电催化性能的影响。结果表明:SnO_2纳米棒呈针尖状,大小均匀,长度为600nm,平均直径约为100nm,Pd粒子高度分散在SnO_2纳米棒表面;在1mol/L KOH+1mol/L C_2H_5OH溶液中,制得的Pd-X(Co、Zn、Fe、Sb)复合催化剂对乙醇氧化均具有较好的催化活性,其中Pd-Zn/SnO_2催化剂表现了最佳的催化性能;当E=-0.2V时,Pd-Zn/SnO_2催化乙醇氧化的峰电流密度可达为30.7mA/cm~2。     

氮掺杂空心碳纳米球嵌入氮掺杂石墨烯负载钯纳米粒子作为甲酸氧化的高效电催化剂（英文）

低成本、高活性、耐久性好的高效电催化剂对直接甲酸燃料电池的应用起着至关重要的作用。本文采用简单经济的方法,研究了以三维层状多孔结构嵌入氮掺杂石墨烯(NG)的氮掺杂空心碳纳米球(NHCN)负载Pd纳米粒子作为直接甲酸燃料电池催化剂。由于具有独特的氮原子掺杂三维互联层状多孔结构,Pd纳米颗粒尺寸较小的Pd/NHCN@NG催化剂具有较大的催化活性表面积、优越的电催化活性、较高的稳态电流密度和较强的抗CO中毒能力,明显超过传统的Pd/C、Pd/NG和Pd/NHCN催化剂对甲酸电氧化的催化性能。通过优化HCN/GO比,当HCN/GO质量比为1∶1时,Pd/NHCN@NG催化剂对甲酸的催化氧化性能最佳,其活性是Pd/C的4.21倍。本工作开发了一种优越的碳基电催化剂载体材料,为燃料电池的发展带来了广阔的应用前景。     

蜂窝状碳负载铁基单原子催化剂的制备及ORR催化性能研究

单原子催化剂(SACs)以近100%的原子利用率以及优秀的催化活性等, 在促进多相催化方面受到了广泛关注。然而, 由于金属原子在高温下易烧结, SACs的合成仍然具有挑战性。本研究利用熔融盐(MS)提供的强极性环境, 制备了以氮掺杂碳为载体的铁基单原子催化剂(Fe SA-NC)。结果表明, Fe SA-NC显示出蜂窝状的多孔形貌, 比表面积高达2072 m²·g^-1, 其中Fe元素的重量百分比含量为0.57%。通过球差电镜直接观察到了孤立存在的Fe单原子, 并通过X射线吸收精细结构(XAFS)分析确定Fe单原子以Fe-N₄配位体形式分散在碳基材料上。Fe SA-NC催化剂在0.1 mol/L KOH 溶液中半波电位为0.85 V, 极限电流密度为5.79 mA·cm^-2, 优于商业Pt/C催化剂。Fe SA-NC催化剂不仅对ORR四电子途径显示出高选择性(H₂O₂产率<2%, 转移电子数为3.9), 同时表现出优秀的抗甲醇性能。     

Pd负载型介孔ZrO2-TiO2复合材料的设计合成及其CO催化氧化性能研究

以介孔结构的复合ZrO₂-TiO₂为载体负载活性组分, 制备了具有高CO催化氧化活性的Pd/ZrO₂-TiO₂与PdCu/ZrO₂-TiO₂负载型催化剂。XRD、TEM研究结果表明: 活性组分Pd、Cu物种可均匀分散于介孔载体中。系统考察了不同的催化剂载体、制备方法和助催化剂等对该介孔复合材料CO催化氧化性能的影响, 结果表明: 以ZrO₂-TiO₂为载体的催化剂其CO催化氧化活性明显优于以介孔Al₂O₃或介孔SBA-15为载体的催化剂; 一步法制备的介孔Pd/ZrO₂-TiO₂催化剂其CO催化氧化的低温活性较浸渍法制备的Pd/ZrO₂-TiO₂有很大提高; 并且Pd和Cu物种共负载的介孔ZrO₂-TiO₂复合催化剂具有最优的CO催化氧化活性, 其CO的完全催化氧化温度可降至170℃, O₂-TPD分析说明Pd和Cu之间的相互作用使得PdCu/ZT催化剂在更低温度具有氧化还原活性。     

还原温度对石墨烯负载Pd颗粒的结构与电催化性能的影响

Pd催化剂对甲酸氧化反应具有出色的电催化性能,适宜的载体有助于改善Pd颗粒的稳定性和分散性,从而使其催化性能得以有效发挥。鉴于此,以硼氢化钠为还原剂,采用化学还原法在不同还原温度(0℃、25℃和50℃)下制备了石墨烯负载Pd颗粒催化剂(Pd/RGO)。采用XRD、Raman、XPS、TGA、TEM和BET等测试方法对该催化剂材料的微观形貌和结构进行了表征,利用循环伏安法和计时电流法测试了催化剂对甲酸氧化反应的电催化性能,着重分析了制备过程中还原温度对催化剂材料结构与电催化性能的影响。结果表明,当还原温度为0℃时,Pd/RGO的比表面积最大,达到261 m~2·g~(-1),Pd颗粒粒径最小,约为4. 16 nm;并且Pd/RGO具有最大的电化学活性面积(3. 02 cm~2),其氧化峰电流密度最高可达1 820 m A·mg~(-1)Pd。     

MoFe/HZSM-5催化剂的制备及其性能的研究

研究以柠檬酸为络合剂,得到Fe3+、Mo6+的络合液,以分子筛(HZSM-5)为载体,采用浸渍法制备了系列负载型MoFe/HZSM-5催化剂,对二甲苯选择性氧化为探针反应,测定其催化性能.催化剂的活性评价结果表明:金属原子的最佳配比为n(Mo):n(Fe)=2.4 :1;在600℃焙烧,反应温度为500℃,气体时空速率5500h-1条件下,对苯二甲醛的选择性达到了最大值85.28%.分别用XRD、FT-IR、DSC对MoFe/HZSM-5进行表征,分析谱图得出了一致性结论,MOFe/HZSM-5的主要活性组分为Fe2(MoO4)3IHZSM-5作为载体,提高了对苯二甲醛的选择性,进而加深了对MoFe/HZSM-5微观结构、性质的了解,MoFe/HZSM-5的高活性、选择性,与其微观结构密不可分,为新型催化剂的研制及其工业应用提供了较好的实验依据.     

钯钌原子比对碳载Pd-Ru催化剂催化H2O2电还原性能影响

利用化学还原法制备了不同原子比的碳载Pd-Ru催化剂,考察了钯钌原子比对碳载Pd-Ru催化剂催化H2O2电还原反应性能的影响。研究结果表明,随着Ru元素的增加,碳载Pd-Ru催化剂的粒径逐渐减小,各催化剂上H2O2电还原反应的起始还原电势稳定在0.82V,电流密度先增大后减小。当Pd∶Ru=1∶1时,PdRu/C催化剂表现了最好的催化性能。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。