Comparison of CuO/Ce0.8Zr0.2O2 and CuO/CeO2 Catalysts for Low-temperature CO Oxidation

CuO/Ce_0.8Zr_0.2O₂ and CuO/CeO₂ catalysts were prepared via a impregnation method characterized by using FT-Raman, XRD, XPS and H₂-TPR technologies. The catalytic activity of the samples for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The influence of the calcination temperature and different supports on the catalytic activity was studied.     

Novel Ce0.8Pr0.2O2 nanotube arrays synthesized by hydrothermal method with excellent catalytic performance

In this research, nanotube arrays of Ce_0.8Pr_0.2O₂ were synthesized on a monolith cordierite honeycomb by the low temperature hydrothermal method. Pre-synthesized ZnO nano-rods on cordierite act as a hard template for Ce_0.8Pr_0.2O₂ deposition. The formation of Ce_0.8Pr_0.2O₂ nanotube arrays was characterized by XRD, selective chemical leaching, BET, and FESEM. The calculated surface area of Ce_0.8Pr_0.2O₂ nanotube arrays was 80?m²/g. The external diameter and the wall thickness of Ce_0.8Pr_0.2O₂ nanotube arrays were 250 and 100?nm, respectively. In addition, Ce_0.8Pr_0.2O₂ nanotube had a length of about 1?μm. Pd decorated nanotube arrays catalyst present a lower light-off temperature and a higher thermal stability than a commercial catalyst in CO conversion catalyst test. Thermal stability of this catalyst is 10 times more than the commercial catalyst at 200?°C. The excellent catalyst performance of Ce_0.8Pr_0.2O₂ nanotube arrays can be attributed to the presence of praseodymium, a high surface area, and a thick wall of Ce_0.8Pr_0.2O₂ nanotubes arrays.     

Effects of sulfation on the activity of Ce0.67Zr0.33O2 supported Pt catalyst for propane oxidation

The sulfated Ce_0.67Zr_0.33O₂ support was prepared by impregnated with sulfuric acid solution, and the influence of sulfation on propane oxidation activity of the corresponding Pt supported catalysts was evaluated. Sulfation of the ceria–zirconia mixed oxides inhibits its intrinsic activity severely but promoted the Pt supported catalysts significantly. It is evidenced by CO adsorption that the interaction between sulfates and platinum makes the latter in more deficient states (Pt^δ+). These metastable Pt^δ+ species are liable to the atmosphere and act as active sites for propane oxidation.     

改进柠檬酸络合法制备CuO-CeO2及其CO低温氧化催化性能

采用改进的柠檬酸络合法即以乙醇代替水作溶剂制备CuO-CeO₂催化剂，应用N₂物理吸附、XRD和H₂-TPR等技术对催化剂进行了表征，并采用微反-色谱装置考察了其对CO低温氧化反应的催化活性。结果表明，常规柠檬酸络合法所制备的CuO-CeO₂催化剂中仅存在一种与CeO₂相互作用较弱、粒子较大的CuO，而采用改进的柠檬酸络合法所制备的催化剂中除此之外还存在与CeO₂相互作用较强、粒子较小的高度分散的CuO，从而具有更高的CO低温氧化活性。     

Deactivation Studies of Rh/Ce0.8Zr0.2O2 Catalysts in Low Temperature Ethanol Steam Reforming

Rapid deactivation of Rh/Ce_0.8Zr_0.2O₂ catalysts during low temperature ethanol steam reforming was studied. A significant build-up of reaction intermediates, instead of carbon deposit, was observed at low reaction temperatures. This appears to be the cause of rapid catalyst deactivation. Co-feed experiments indicated that possible intermediate products acetone and ethylene caused more severe catalyst deactivation than other oxygenates such as acetic acid and acetaldehyde.     

Investigation on bi-layer coating with La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7/YSZ prepared by laser cladding

Thermal barrier coatings are an effective technology for improving the high-temperature performance of hot section components in gas turbine engine. Due to their excellent properties, high-entropy oxides are considered to be promising materials for thermal barrier coatings. Laser cladding is a coating preparation technology and the top coat prepared by laser cladding technology has an important application value for thermal barrier coatings. In this work, to improve the thermal cycling behavior of the La₂(Ti_0.2Zr_0.2Sn_0.2Ce_0.2Hf_0.2)₂O₇ high-entropy oxide coating, a bi-layer coating with the La₂(Ti_0.2Zr_0.2Sn_0.2Ce_0.2Hf_0.2)₂O₇ high-entropy oxide layer and the YSZ layer was designed and fabricated by laser cladding on the NiCoCrAlY alloy surface. The microstructure, phase and mechanical properties of the coating were analyzed by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and micro-hardness and nanoindentation tests, respectively. The results show that a bi-layer La₂(Ti_0.2Zr_0.2Sn_0.2Ce_0.2Hf_0.2)₂O₇/YSZ coating was successfully prepared by the laser cladding method, and shows good bonding at the interface between the layers. The high-entropy oxide layer maintains a relatively stable defective fluorite structure and its microstructure exists in the stable cellular and dendrite crystalline state after laser cladding. The high-entropy oxide layer prepared by laser cladding showed an average elastic modulus of 167 GPa and an average hardness of 1022.8HV in nanoindentation tests. Thermal cycling of the coating was carried out at 1050 °C. Failure of the bi-layer coating occurred after 60 thermal cycles at 1050 °C. Thermal stresses between different layers are calculated during thermal cycling. Due to its excellent mechanical properties, the bi-layer coating with the La₂(Ti_0.2Zr_0.2Sn_0.2Ce_0.2Hf_0.2)₂O₇ high-entropy oxide and YSZ layers is expected to become an effective high-entropy oxide thermal barrier coating.     

Preparation of dual-phase composite BaCe0.8Y0.2O3/Ce0.8Y0.2O2 and its application for hydrogen permeation

Dual-phase ceramic membranes composed of BaCe_0.8Y_0.2O₃ (BCY) and Ce_0.8Y_0.2O₂ (CYO) were successfully synthesized by solid state reaction method for hydrogen permeation. The influences of the BCY/CYO volume ratios on phase composition, microstructure, chemical stability and electrical property were investigated. The hydrogen permeation of the dual-phase composite was characterized as a function of temperature and feed side hydrogen partial pressure. The results showed that there was no reaction between the two constituent oxides observed under the preparation conditions. The dual-phase composite with different BCY/CYO volume ratios after sintering at 1550 °C exhibited dense structure, as well as good stability in 4% H₂/Ar, wet Ar and pure CO₂ atmosphere. The conductivity of the dual-phase composite increased with the content of CYO increasing and 30BCY–70CYO exhibited the highest total conductivity of 2.6×10⁻² S cm⁻¹ at 800 °C in 4% H₂/Ar. The hydrogen permeability of 30BCY–70CYO sample was improved as the temperature and the hydrogen partial pressure in feed gas increased. The hydrogen permeation flux of 1.7 μmol cm⁻² s⁻¹ was achieved at 850 °C.     

Perovskite-type oxide ACo0.8Bi0.2O2.87 (A=La0.8Ba0.2): a catalyst for low-temperature CO oxidation

Perovskite-type oxide ACo_0.8Bi_0.2O_2.87 (A=La_0.8Ba_0.2) has been investigated as a catalyst for the oxidation of carbon monoxide. X-ray diffraction results revealed that the catalyst is single-phase and cubic in structure. The results of chemical analysis indicated that in ACo_0.8Bi_0.2O_2.87, bismuth is pentavalent whereas cobalt is trivalent as well as bivalent; in La_0.8Ba_0.2CoO_2.94, cobalt ions exist as Co³⁺ and Co⁴⁺. The substitution of Bi for Co enhanced the catalytic activity of the perovskite-type oxide significantly. Over the Bi-incorporated catalyst, at equal space velocities and with the rise in CO/O₂ molar ratio, the temperature for 100% CO conversion shifted to a higher range; at a typical space velocity of 30000 h^–1 and a CO/O₂ molar ratio of 0.67/1.00, 100% CO conversion was observed at 250°C. Over ACo_0.8Bi_0.2O_2.87, at equal CO/O₂ molar ratio, the temperature for 100% CO conversion decreased with a drop in space velocity; the lowest being 190°C at a space velocity of 5000 h^–1. The result of O₂-TPD study illustrated that the presence of Bi ions caused the lattice oxygen of La_0.8Ba_0.2CoO_3– to desorb at a lower temperature. The results of TPR, ¹⁸O/¹⁶O isotopic exchange, and CO-pulsing investigations demonstrated that the lattice oxygen of the Bi-doped catalyst is highly mobile.     

火焰喷雾合成法制备La0.8Sr0.2Mn1-xCuxO3催化氧化CO性能研究

采用火焰喷雾合成法制备了Sr²⁺、Cu²⁺分别取代A、B位的La_0.8Sr_0.2Mn_1-xCu_xO₃ （x=0,0.1,0.2,0.3,0.4）钙钛矿催化剂,并用于CO催化氧化实验,研究了水蒸气和CO₂对催化剂CO氧化活性的影响。对不同取代量La_0.8Sr_0.2Mn_1-xCu_xO₃ 催化剂进行了XRD、SEM、EDS、BET、XPS、H₂-TPR和O₂-TPD等表征测试。结果表明,火焰喷雾合成法制备的钙钛矿催化剂具有良好的钙钛矿相、疏松多孔结构和催化氧化活性。其中,La_0.8Sr_0.2Mn_0.9Cu_0.1O₃分别在119.4℃和133.3℃实现50%和90%的CO转化率。掺杂水蒸气和CO₂会与CO在催化剂表面形成竞争吸附,导致5种催化剂性能衰减,但La_0.8Sr_0.2Mn_0.9Cu_0.1O₃仍能在150.2℃实现90%的CO催化转化,在连续稳定性催化氧化测试中,5种催化剂性能衰减不超过10%。结合上述CO催化氧化实验,火焰喷雾合成法制备的催化剂具有良好的稳定性和催化活性,适合制备高CO催化氧化活性的钙钛矿催化剂。     

Study on catalytic performance of CeO2/CuO catalysts for preferential CO oxidation

采用水热法合成纳米尺寸的CuO,然后采用微乳液法或浸渍法将CeO₂负载在CuO上制备逆负载的CeO₂/CuO催化剂。通过X射线衍射（XRD）、程序升温还原（TPR）、比表面分析（BET）和富氢气中CO优先氧化活性测试等研究手段对催化剂进行了表征。研究发现,CeO₂/CuO催化剂的活性和选择性与CeO₂和CuO颗粒的尺寸密切相关,大颗粒的CuO载体有利于提高催化剂的选择性;小颗粒的氧化铈负载在大颗粒的氧化铜上,可以产生更多两相接触界面,有助于提高催化剂的活性。     

Formation and properties of Ca2+ substituted (Ce0.2Zr0.2Ti0.2Sn0.2Hf0.2)O2 high-entropy ceramics

Five equimolar multicomponent oxides were synthesized by replacing one of five cations in (Ce_0.2Zr_0.2Ti_0.2Sn_0.2Hf_0.2)O₂ with Ca²⁺. The results reveal that except for the one in which Ce⁴⁺ replaced by Ca²⁺, the other four components can form single-phase high-entropy fluorite oxides (HEFOs) at different temperatures, which indicates that Ce⁴⁺ is very important for the formation of single-phase HEFOs. The sintering behavior, lattice parameter and properties containing density, porosity, flexural strength and thermal conductivity of the four single-phase HEFOs were investigated. With the change of substituted ions, grain size, relative density, flexural strength and thermal conductivity of the materials vary greatly, which are correlated to the size disorder and mass disorder of these materials. The results of this paper provide a reference for the composition designing and performance tailoring of equimolar HEFOs.     

Influence of the nature of the reducible support on CO oxidation kinetics of supported Rhδ+ catalysts: SnO2 versus Ce0.68Zr0.32O2

CO–O₂ kinetics was studied on Rh(0.3 wt%)/SnO₂ and compared with that reported previously on Rh/Ce_0.68Zr_0.32O₂. The lower oxygen mobility on SnO₂ and the stronger bonding of CO with the Rh^δ+ sites of Rh/SnO₂, are suggested to account for the lower CO oxidation activity of Rh/SnO₂ compared with that reported on Rh/Ce_0.68Zr_0.32O₂.     

Electromechanical properties of Ba(Zr0.2Ti0.8)O3 ceramics prepared by spark plasma sintering

Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared by spark plasma sintering (SPS) and conventional sintering. The dynamic field-induced displacement and small-signal remnant piezoelectric constant measured by a resonant–antiresonant frequency method were evaluated. By normal sintering, the density, grain size, and dielectric constant of the ceramics increased with sintering temperature. The BZT20 ceramics prepared by SPS were characterized by linear field-induced strain. In response to the application of post-annealing at 1300 °C, BZT20 ceramics exhibited linear strain loop and high field-induced strain corresponding to dynamic strain/field d₃₃ at 20 kV/cm of 290 pm/V. The remnant piezoelectric properties of the BZT20 ceramics were found to largely depend on the preparation conditions, including the sintering temperature and annealing temperature. The BZT20 ceramics prepared by SPS and post-annealed at 1300 °C showed Q_m and k_p values of 325 and 25.1 (%), respectively.     

Al2O3掺杂方式对Ce0.8Sm0.2O1.9电解质结构和性能的影响

研究了Al2O3掺杂方式对Ce0.8Sm0.2O1.9 (SDC) 材料性能的影响。用XRD、SEM、XEDS和热膨胀系数仪等检测手段对样品的晶体结构、力学、热学、显微结构和微区元素进行检测分析。结果表明：采用低温燃烧一步合成法制备的样品其力学性能、烧结性和离子电导率均优于采用铝溶胶直接添加法所制备的样品,其主要原因在于铝溶胶直接添加法会在SDC材料中产生残留Al2O3,并富集在晶界处形成晶界夹杂,阻碍了氧离子迁移。     

Ce0.8Y0.2O1.9氧化物的烧结及晶粒生长动力学研究

通过对Ce0.8Y0.2O1.9(YDC)素坯烧结行为的考察,得到了试样的密度、晶粒大小随烧结温度(1000~1500℃)的变化规律。利用扫描电子显微镜对烧结体的晶粒尺寸分布进行统计分析表明:Ce0.8Y0.2O1.9晶粒生长在两个烧结温度区域内分别遵循不同的速率方程,在1000~1300℃较低的温度范围内,晶粒成长的活化能较小(171.1 kJ/mol),即烧结温度对晶粒成长的影响较小;在1300~1500℃较高的温度范围,晶粒生长的活化能较大(479.8 kJ/mol),即晶粒成长对烧结温度的高低表现为非常敏感,并且晶粒尺寸分布显著宽化。烧结体的密度在1000~1400℃范围内随温度的升高几乎直线上升,在1400℃时相对密度达98.5%,1400℃以上则提高的幅度变得很小。     

Improved catalytic activity of SiC supported Ni catalysts for CO2 reforming of methane via surface functionalizations

The effect of surface functionalizations on structural and catalytic properties of SiC supported Ni catalysts for CO₂ reforming of methane has been investigated. Commercial SiC was surface functionalized to form a carbon composite (C-SiC) and an N-doped carbon composite (N-C-SiC) at the interface of SiC. Micro- and meso-pores were generated after surface functionalizations. The reforming activity followed the sequence of Ni/N-C-SiC > Ni/C-SiC > Ni/SiC, which can be rationalized by the enhanced Ni dispersion and enriched basic sites on the functionalized catalysts. The present work demonstrates surface functionalization as a simple method to improve the catalytic activity of SiC supported catalysts.     

大孔SiO_2载体制备La_(0.8)Sr_(0.2)CoO_3及其对NO+CO的催化性能

以具有高比表面积的大孔SiO_2为载体,采用浸渍法,通过控制浸渍液浓度的不同原位制备不同负载率的稀土钙钛矿型复合氧化物La_(0.8)Sr_(0.2)CoO_3/SiO_2样品。利用X射线衍射、比表面积、扫描电镜和X射线光电子能谱等分析方法对样品进行表征,结果表明,载体表面均匀负载La_(0.8)Sr_(0.2)CoO_3,且随着负载率增加,样品比表面积下降。考察不同负载率的La_(0.8)Sr_(0.2)CoO_3/SiO_2样品对NO+CO的催化活性,结果表明,与比表面积和结晶度相比,负载率在该催化实验体系中是影响最大的因素,综合催化效果最好的样品负载La_(0.8)Sr_(0.2)CoO_3质量分数为50.47%。     

Catalytic combustion of SOFC stack flue gas over CuO and Mn2O3 supported by La0.8Sr0.2Mn0.67Cu0.33O3 perovskite

An efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H₂, and CH₄ in flue gas of solid oxide fuel cell (SOFC) stack. Amorphous Cu‐Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650°C). La_0.8Sr_0.2Mn_0.67Cu_0.33O₃ perovskite (LSMC(p)) supported CuO or Mn₂O₃ exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800°C for 24 h, T₅₀ of CO, H₂ and CH₄ was achieved at 170, 230, and 600°C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu²⁺‐Mn³⁺ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 940–949, 2018