首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 93 毫秒
1.
Co/ZrO2催化剂的结构及TPR性能研究   总被引:1,自引:0,他引:1  
采用XRD和TPR技术研究了Co-Zr-O体系催化剂的物相结构及还原性能,并以CO氧化反应为探针考察了催化剂的氧化活性,结果表明,钴的存在会阻止t-ZrO2→混合相→m-ZrO2的转变和ZrO2颗粒的增长,高温焙烧后,部分钴氧化物与载体ZrO2形成固溶体,Co/ZrO2催化剂中的钴以Co3O4的形式存在,钴锆之间的相互作用有利于钴的分散,随着Co负载量增加,催化剂的CO氧化活性提高。  相似文献   

2.
ZrO2在Pd/Al2O3催化剂中的助剂作用   总被引:6,自引:2,他引:4  
用流动反应法考察了富氧或贫氧气氛中添加ZrO2的Pd/Al2O3催化剂上CO的催化氧化反应,并用XRD、TPR和TPD-MS等技术研究了助剂ZrO2与γ-Al2O3间的相互作用对催化剂上氧物种的还原和脱出-恢复行为的影响,结果表明,基质γ-Al2O3与ZrO2能发生相互作用,添加6%ZrO2的催化剂氧化活性最好,添加适量的ZrO2有利于催化剂上氧物种的脱出-恢复,从而促进CO氧化活性及表面活泼氧物  相似文献   

3.
用流动反应法和TPSRMS等技术研究了CO在Pd/γAl2O3和含有ZrO2的催化剂上的吸脱附行为、表面反应及催化氧化活性,同时用XRD技术测定了催化剂的物相结构。结果表明,在Pd/γAl2O3催化剂中用浸渍法添加ZrO2或掺杂超细ZrO2后,催化剂的氧化活性均有明显提高;COTPSR的实验结果表明,CO在氧化态Pd催化剂上程序升温脱附过程中主要与表面氧发生氧化反应,而在还原态Pd催化剂上发生歧化反应,并发现CO2的脱附量及脱附峰温次序与对CO的氧化活性有一致的对应关系。  相似文献   

4.
ZrO2载体上Pd,Ag,Co催化剂用于甲烷完全氧化反应的研究   总被引:5,自引:2,他引:3  
用浸渍法制备了Pd/ZrO2、Ag/ZrO2和Co/ZrO2等催化剂用一完全氧化反应。实验表明,对Pd/ZrO2催化剂,焙烧温度对共催化生影响很大,最佳焙烧温度为280℃。对Pd/ZrO2催化剂,最佳Pd负一为10W%。随总流量增大,甲烷论率下随O2/CH4进料比减小,甲烷转化率下降。其它负载型金属催化剂如Ag,Co等用于甲烷氧化反应中具有一定的活性,但活性低于Pd。Pd-Co双金属催化剂可望是理  相似文献   

5.
通过CuO/ZrO2及含Y或La助剂的CuO/ZrO2催化剂对OC/H2合成甲醇性能的研究,发现稀土助剂能有效地提高该催化剂的活性。XRD结果说明,CuO|ZrO2中加入Y或La助剂可使氧化铜处于较高的分散状态。TPR结果揭示CuO/ZrO2催化剂中存在着在室温就很容易被氧人的铜,它在催化剂中含量的增加导致催化剂活性的提高,是关切的活性组份。助剂的加入使这种易被氧化的铜含量增加。XPS表面分析结果  相似文献   

6.
吴泽彪  朱毅青 《催化学报》2000,21(2):129-132
考察了CO2加氢合成CH3OCH3反应中ZrO2含量对Cu-ZnO-SiO2-ZrO2催化剂的影响,采用TPR,XRD,BET和TEM等技术对催化剂的结构形态、表面性质和ZrO2的作用进行了研究,结果表明,催化剂中加入ZrO2能提高催化剂的比表面积及CO2转化率和CH3OCH3产率,降低最佳反应温度;ZrO2含量以2%~3%为佳,催化剂中的CuO以种形式存在:小晶粒CuO,聚集的无定形CuO及均匀  相似文献   

7.
通过活性测定,XRD、TG-DTA表征,考察了共沉淀法制备的铜锌锆合成甲醇催化剂中ZrO_2对物相结构、催化活性及热稳定性的影响。结果表明,ZrO_2能显著提高CO/H_2合成甲醇的催化活性和热稳定性。催化剂母体、氧化态和还原态的物相并未发生变化,仍分别为:Cu_2(OH)_3NO_3,(Cu,Zn)_5(CO_3)_2(OH)_6,(Cu,Zn)_2CO_3(OH)_2,Zn_5(CO_3)_2(OH)_6;CuO、2nO;Cu,ZnO。ZrO_2使催化剂各组分的结晶度变得更差,晶粒更细。实验证明催化剂中ZrO_2主要以无定形状态存在,也不排除与其它组分形成固溶体。本文还探讨了ZrO_2提高催化活性和热稳定性的原因。认为ZrO_2既起了载体的高分散作用,间隔活性组分作用,又起了增加和稳定活性中心的促进剂作用。  相似文献   

8.
CO/H2合成甲醇CuO—ZnO—ZrO2催化剂的研究   总被引:4,自引:0,他引:4  
通过活性测定,XRD、TG-DTA表征,考察了共沉淀法制备的铜锌锆合成甲醇催化剂中ZrO2对物相结构、催化活性及热稳定性的影响。结果表明,ZrO2能显著提高CO/H2合成甲醇的催化活性和热稳定性。催化剂母体、氧化态和还原态的物相并未发生变化,仍分别为:Cu2(OH)3NO3,(Cu,Zn)5(CO3)2(OH)6,(Cu,Zn)2CO3(OH)2,Zn5(CO3)2(OH)6;CuO、ZnO;Cu  相似文献   

9.
用浸渍沉淀法分别制备了负载型ZrO2/Al2O3和ZrO2(MgO、K2O、CeO2、La2O3)/Al2O3催化剂.用XRD、BET、TPD对催化剂的晶相结构、比表面积、孔径分布、表面酸碱性等进行了表征;同时以CO2和CH3OH为探针用原位红外对催化剂的吸附行为进行研究.结果表明,掺杂氧化物有效的阻止ZrO2晶粒的团聚,并提高了催化剂的比表面积和平均孔径;CeO2的添加有利于碱性中心数的增多,La2O3有利于酸性中心数的提高.原位红外结果表明CH3OH能在ZrO2(CeO2、La2O3)/Al2O3催化剂表面发生解离吸附,而CO2在催化剂表面均出现单齿态吸附.CO2和CH3OH在常压下直接合成碳酸二甲酯(DMC)反应中ZrO2(CeO2、La2O3)/Al2O3催化剂表现出较好的催化活性和选择性.  相似文献   

10.
Cu/ZrO2-Al2O3上表面氧物种脱附及其对催化性能的影响   总被引:1,自引:0,他引:1  
采用XRD,TPD-MS和TPR方法研究了ZrO2的改性对CuO/γ-Al2O3催化剂上铜物种人散状态,表面氧物种的脱附和恢复性能,铜物种还原再氧行为的影响,并CO氧化反应为探针考察了催化剂的氧化活性,结果表明,ZrO2的存在的铜物种在γ-Al2O3载体上的分散容量降低,促进CuO/γ-Al2O3催化剂上表面氧物种的脱附,同时有效地促进铜物种的还原,从而增加CO的氧化活性,实验还发现热处理条件对催  相似文献   

11.
Silica supported gold nanoparticles were synthesized and promoted by lanthanum oxide as dopant. The influences of La_2O_3 and silica textural structure on the gold dispersion, formation of active species, crystalline composition and the reacting role of dopants were studied in detail. The characterization results suggested that the dispersion of gold nanoparticles depended on the textural structure of silica without lanthanum oxide doping where small mesopores are more preferable to disperse gold nanoparticles. The addition of lanthanum oxide largely increased the dispersion of gold nanoparticles and oxygen active sites independent of the textural structure of silica support. The interaction between lanthanum oxide and silica enhanced by the synergy facilitated the release of oxygen vacancies and transition of active oxygen species. In addition, the chemical properties were greatly changed after lanthanum oxide addition which was only inconspicuously impacted by the initial textural structure of silica supports, shedding light on the further design of economic gold catalyst based on simple synthesis method.  相似文献   

12.
Hexagonal arrangement of iron oxide nanoparticles was fabricated by utilizing a single-layered film of diblock copolymer micelles. The synthesis was directly performed on the solid substrate by oxygen plasma with preserving the dimensional order of micelles so that separate procedures for synthesis and deposition of nanoparticles were not necessary. Since the oxygen plasma treatment also eliminated polymers, pure patterns of iron oxide nanoparticles were obtained. Moreover, easy control over the size of nanoparticles enabled us to selectively create a ferrimagnetic or a superparamagnetic pattern of iron oxide nanoparticles without altering the fabrication process.  相似文献   

13.
To obtain an ideal electrocatalysts for hydrogen fuel cells, we investigated group 4 and 5 oxide-based compounds because of their high degree of freedom. First-principles calculations revealed that oxide surfaces such as those of titanium oxide could break down the universal scaling to achieve the ideal state of the oxygen reduction reaction. We experimentally clarified that the active sites were oxygen vacancies for tantalum and zirconium oxides, in addition to doped foreign elements and crystalline structures for titanium oxide. We successfully demonstrated that precious metal-free and carbon-free oxide-based cathodes have high quality active sites and superior durability in 0.1 M sulfuric acid at 80°C. Our strategy was developed as follows: (1) Active sites are created on the oxide surface by modifying the crystalline structure and electronic states and (2) electrons participating in the oxygen reduction reaction are supplied by nanosized oxide particles and oxide films through the tunneling effect of electrons.  相似文献   

14.
The method of the chemical synthesis of reduced graphene oxide was developed. Sodium hypophosphite and sulfi te were used as reducing agents. The formation of reduced graphene oxide was confi rmed by several methods. Volt-ampere characteristics of electrodes based on reduced graphene oxide were investigated in an experimental model of an oxygen fuel cell with an alkaline electrolyte. Characteristics of oxygen electrodes based on reduced graphene oxide were stable over semiannual tests. The resulting reduced graphene oxide is a promising material for oxygen electrodes of chemical current sources.  相似文献   

15.
The effect of oxygen vacancies in the anodic oxide film on passive titanium on the kinetics of the oxygen electrode reaction has been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Oxide films of different donor density were prepared galvanostatically at various current densities until a potential of 20.0 VSHE was achieved. The semiconductive properties of the oxide films were characterized using EIS and Mott-Schottky analysis, and the thickness was measured using ellipsometry. The film thickness was found to be almost constant at ∼44.7 ± 2.0 nm, but Mott-Schottky analysis of the measured high frequency interracial capacitance showed that the donor (oxygen vacancy) density in the n-type passive film decreased sharply with increasing oxide film formation rate (current density). Passive titanium surfaces covering a wide range of donor density were used as substrates for ascertaining relationships between the rates of oxygen reduction/evolution and the donor density. These studies show that the rates of both reactions are higher for passive films having higher donor densities. Possible explanations include enhancement of the conductivity of the film due to the vacancies facilitating charge transfer and the surface oxygen vacancies acting as catalytic sites for the reactions. The possible involvement of surface oxygen vacancies in the oxygen electrode reaction was explored by determining the kinetic order of the OER with respect to the donor concentration. The kinetic orders were found to be greater than zero, indicating that oxygen vacancies are involved as electrocatalytic reaction centers in both the oxygen evolution and reduction reactions. This paper was submitted in honor of the many contributions to electrochemistry that have been made by Professor Boris Grafov. The article is published in the original.  相似文献   

16.
Density functional theory (DFT) studies were performed to investigate the influence of coadsorbates on the nitrogen oxide dissociation on the vicinal rhodium(311) surface. This study amplifies prior studies on the dissociation of oxygen and nitrogen oxide on the (111) facet of rhodium. The influence of coadsorbates on the kinetic parameters and thermochemistry of the NO dissociation on Rh311 was studied. In addition, the activation energy and thermochemistry of this reaction were determined as a function of oxygen preoccupation/initial coverage. Steric and electronic effects and their influence on the dissociation reaction were examined. The results are discussed in the face of an NOx dissociation catalyst system proposed by Nakatsuji.  相似文献   

17.
The effects of oxygen vacancies and zinc interstitials on the structure and energy of zinc oxide were studied with the semiempirical MO method MSINDO. Cyclic clusters were chosen as model systems. Single and multiple removal of oxygen atoms and zinc interstitials in zinc oxide served to determine the defect formation energy and the band gap. The interaction between two and three oxygen vacancies was investigated. The vacancies cause a decrease of the band gap, which originates from an occupied defect level. This is also found for zinc interstitials under zinc rich conditions. The defect formation energy of such zinc interstitials is found to be lower than that of oxygen vacancies at 0 K but decreases for oxygen vacancies and increases for zinc interstitials with increasing temperature.  相似文献   

18.
We report on the high-efficiency surface-induced dissociation of benzene and cyclohexane polyatomic ions after scattering from a rhenium oxide surface with a kinetic energy of 5–290 eV. Rhenium oxide was prepared by directly heating a rhenium metal foil, under 10?5 mbar partial oxygen pressure, at about 1000 K. Rhenium oxide is characterized by a very high work function of 6.4 eV and thus minimizes ion reneutralization probabilities. The catalytic combustion of surface organic impurities with oxygen ensures good long-term stability. We found that the surface-induced dissociation ion current is 70 times larger on rhenium oxide than on bare rhenium or stainless steel. Absolute scattered ion yields of about 50% were measured. The implications of surface-induced dissociation on mass spectrometry in supersonic molecular beams are mentioned.  相似文献   

19.
The oxygen isotopic exchange technique is a powerful tool to investigate the oxygen transport kinetics in an oxide solid. In a solid oxide fuel cell, isotopic surface exchange and diffusion coefficients are classically determined by using the Isotopic Exchange Depth Profiling method followed by ex situ SIMS characterizations. Despite its relevance, the utilization of in situ or operando techniques to measure the isotopic exchange under an electrical bias remains marginal. We developed here a set-up which enables operando monitoring of oxygen exchange in SOFC type cells under polarization. The system has been used for studying the oxygen mobility dependency upon polarization on a symmetrical Pt/YSZ/Pt cell (YSZ: yttria-stabilized zirconia). Homomolecular and heterolytic exchange reactions were undertaken to investigate the oxygen activation step and discriminate the limiting step among the sequence of elementary steps which constitute the oxygen transport process in the SOFC system. Oxygen ions incorporation into the dense ionic conductor was identified to be the rate determining step, and its first order rate constant dependency on applied potential was established.  相似文献   

20.
Atomistic simulations employing dynamic charge transfer between atoms are used to investigate ultra-thin oxide growth on Al(100) metal substrates in the presence of an ac electric field. In the range of 1-10 GHz frequencies, the enhancement in oxidation kinetics by ~12% over natural oxidation can be explained by the Cabrera-Mott mechanism. At field frequencies approaching 0.1-1 THz, however, we observe a dramatic lowering of the kinetics of oxygen incorporation by ~35% compared to the maximum oxidation achieved, which results in oxygen non-stoichiometry near the oxide-gas interface (O/Al ≈ 1.0). This is attributed to oxygen desorption from the oxide surface. These results suggest a general strategy to tune oxygen concentration at oxide surfaces using ac electric fields that could be of interest in diverse fields related to surface chemistry and applications such as tunnel barriers, thin dielectrics and oxide interfaces.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号