钙钛矿型La1+X/2Sr1-x/2Co1-xCuxO3催化CO氧化活性与表征

The catalytic activity and the reactive properties of perovskite-type oxides catalysts La(1+x/2)Sr(1-x/2)Co1-xCuxO3 for CO oxidation reaction were investigated. Results showed that the catalytic activity for CO oxidation reached to a maximum when x＝0.4. The temperature for complete CO oxidation under atmospheric and experimental conditions was 168℃. According to the stoicheometry of catalyst, all catalysts were oxygen defect compounds. The active oxygen species on this catalyst was the adsorbed oxygen which was adsorbed on the surface lattice oxygen defect. It was also found that Co4+ existed in the catalysts and the sufrace active oxygen species was caused by the Co4+. It was concluded that CO oxidation reaction on this catalyst was carried out by the valence change between Co3+ and Co4+ which was adjusted by the adsorbed oxygen.     

La1-xSrxFeO3钙钛矿型氧化物中的晶格氧用于甲烷部分氧化制合成气

采用燃烧法制备了Sr掺杂钙钛矿型氧化物La_1-xSr_xFeO₃（x=0,0.3,0.5,0.9）载氧体,对载氧体分别进行X射线衍射、扫描电镜和H₂程序升温还原反应表征,在热重循环装置和固定床反应装置上考察甲烷与载氧体晶格氧的部分氧化反应.结果表明,La_1-xSr_xFeO₃氧化物中的晶格氧适用于甲烷部分氧化制合成气,晶格氧的得失是一个可逆过程,Sr的掺杂提高了载氧体的供氧能力,5次循环后载氧体得失晶格氧的能力没有明显的衰减.从甲烷转化率、n（H₂）/n（CO）比以及H₂和CO的选择性等方面来考虑,x=0.3-0.5比较理想,甲烷转化率维持在70%左右,气体产物中n（H₂）/n（CO）约为2,CH₄没有发生明显的裂解.     

复合氧化物催化剂La0.5Sr0.5Ni1-yCuyO3上CO氧化反应与活性氧种的研究

对复合氧化物催化剂La0.5Sr0.5Ni1-yCuyO3上表面活性氧种的研究已有报导[1～3]. 一般认为,在该催化剂中主要有两类表面氧物种,即表面吸附氧和表面晶格氧,它们和气相氧之间存在着动态平衡,可以互相转化. 我们通过TGA、 XPS及瞬变应答实验对催化剂La0.5Sr0.5Ni1-yCuyO3上表面氧种的表征,证明了低温时对CO起活性作用的是表面吸附氧,而且由于B位Ni离子被Cu离子部分取代,使催化剂对CO氧化反应的完全转化活性温度有所下降. 这一实验结果为开发低温高效汽车尾气净化催化剂提供了有益的信息.     

Reactivity of La1 ? xSrxFeO3 ? y (x = 0–1) Perovskites in Oxidation Reactions

Oxygen species and their reactivity in La_{1 − x} Sr _x FeO_{3 − y} perovskites prepared using mechanochemical activation were studied by temperature-programmed reduction (TPR) with hydrogen and methane. The experimental data were compared with data on the catalytic activity in oxidation reactions. It was found that the rates of CO and methane oxidation on the perovskites in the presence of gas-phase oxygen correlated (k = 0.8) with the amount of reactive surface oxygen species that were removed by TPR with hydrogen up to 250°C. Maximum amounts of this oxygen species were released from two-phase samples (x = 0.3, 0.4, and 0.8), which exhibited an enhanced activity in the reaction of CO oxidation. In the absence of oxygen in the gas phase, methane is oxidized by lattice oxygen. In this case, the process activity and selectivity depend on the mobility of lattice oxygen, which is determined by the temperature, the degree of substitution, the degree of reduction, and the microstructure of the oxide. Thus, the high mobility of oxygen, which is reached at high concentrations of point defects or interphase/domain boundaries, is of importance for the process of deep oxidation. However, the process of partial oxidation occurs in single-phase samples at low degrees of substitution (x = 0.1–0.2). __________ Translated from Kinetika i Kataliz, Vol. 46, No. 5, 2005, pp. 773–779. Original Russian Text Copyright ? 2005 by Isupova, Yakovleva, Alikina, Rogov, Sadykov.     

Reactivity of surface and bulk oxygen in La1-xCaxFeO3-y system with respect to methane oxidation

The reactivity and mobility of the surface and lattice oxygen in a La_1-xCa_xFeO_3-y system prepared via a ceramic route were studied by using CH₄-TPR. While the middle-temperature (400-700^oC) oxygen lattice mobility reaches maximum for samples with disordered anion vacancies, the high-temperature lattice oxygen flux appears to be controlled by a rapid transfer along disordered domain walls. In the high-temperature range, a high selectivity to syngas of methane oxidation by the lattice oxygen was achieved both for pure lanthanum ferrite and for samples with a microdomain structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relationship between oxygen species and activity/stability in heteroatom (Zr,Y)-doped cerium-based catalysts for catalytic decomposition of CH3SH

CeO₂, Ce_1–xZr_xO₂, and Ce_1–xY_xO_2–δ (x = 0.25, 0.50, 0.75, and 1.00) have been rapidly synthesized to estimate their catalytic behavior in decomposing CH₃SH. The role of oxygen vacancies, and the relationship between the oxygen species and catalytic properties of CeO₂ and Zr-doped and Y-doped ceria-based materials are investigated in detail. Combining the observed catalytic performance with the characterization results, it can be deemed that surface lattice oxygen plays a critical role in methanethiol catalytic conversion over cerium oxides. Ce_0.75Zr_0.25O₂ shows higher catalytic activity for CH₃SH decomposition due to the large amount of surface lattice oxygen, readily available oxygen species, and excellent redox properties. Ce_0.75Y_0.25O_2–δ displays better catalytic stability owing to the greater number of oxygen vacancies that would promote bulk lattice oxygen migration to the surface of the catalyst in order to replenish surface lattice oxygen. In addition, the results show that the difference in chemical valence between Ce and the heteroatoms would strongly influence the amount of surface lattice oxygen as well as the mobility of bulk-phase oxygen in these catalysts, thus affecting their activity and stability.     

BaCo1-xFexO3-δ缺陷钙钛矿NOx储存还原催化剂的制备、结构与性能

制备了B位Fe取代的BaCo1-xFexO3-δ系列缺陷钙钛矿型NOx储存还原(NSR)催化剂,考察了其储存NOx与抗硫性能;应用N2吸附-脱附,X射线衍射,红外光谱,程序升温还原和程序升温脱附等技术对催化剂进行了表征.结果表明,Fe的取代提高了BaCoO3的抗硫能力,当x=0.4时,样品具有相对最大的NOx储存量,且...     

Oxygen States in Oxides with a Perovskite Structure and Their Catalytic Activity in Complete Oxidation Reactions: System La1 – x Ca x FeO3 – y (x = 0–1)

Oxygen states in the La_{1 – x} Ca _x FeO_{3 – y} perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH₄ oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La_{1 – x} Ca _x FeO_{3 – y} series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La_{1 – x} Ca _x FeO_{3 – y} samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.     

Characterization and catalytic performance of Co, Ni and W trimetallic carbides

Summary For Pr-doped ceria Ce_1-xPr_xO_2-y prepared by the Pechini route and promoted with Pt, the mobility and reactivity of lattice oxygen were found to depend on the Pr content, which seems to determine the density of surface and bulk anion vacancies and domain boundaries.     

Characterization and CO oxidation catalytic behavior of CuO/CeO2 catalysts

Summary Effects of the lattice oxygen mobility, Pt dispersion and the surface features of Pt/Ce_1-xPr_xO_2-y samples on their performance in the selective oxidation of methane into syngas, in the steam and dry reforming of methane at short contact times are considered.     

Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor

The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO ₃ pellets. Lattice oxygen species in BaTiO ₃ play an important role in the formation of N ₂ O and the oxidation of CH ₄ . The oxidation products such as CO and CO ₂ were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N ₂ O and NO _x were independently formed in the N ₂–O ₂ reaction, suggesting that different oxygen species give N ₂ O and NO _x. N ₂ O was produced by the oxidation of molecular nitrogen with lattice oxygen species.     

Preparation and catalytic oxidation performance andOF Pr2-xSrxCoO4+λwithK2NiF4structure

Summary A series of Pr_2-xSr_xCoO_4+λmixed oxides were prepared and used successfully for oxidation of CO and C₃H₈. The results show that Pr_2-xSr_xCoO_4+λdisplay K₂NiF₄-type structure and their catalytic activities are closely correlated with the concentration of Co³⁺, mobile lattice oxygen and oxygen vacancy.</o:p>     

Ce-Fe-Zr-O/MgO整体型氧载体用于化学链部分氧化甲烷制合成气

以MgO为载体,采用球磨法制备了Ce-Fe-Zr-O/MgO粉末状氧载体,进而采用挤压成型法制备了整体型氧载体。研究了两种氧载体化学链部分氧化甲烷制合成气的性能,并通过XRD、H₂-TPR对氧载体进行表征。结果表明,粉末状氧载体中的储氧组分以Ce-Fe-Zr-O固溶体形式存在,而整体型氧载体的制备过程会导致Zr、Fe游离氧化物的形成。粉末状氧载体和整体型氧载体上均存在表面晶格氧和体相晶格氧,其中,体相晶格氧具有高选择性氧化甲烷的性能,可以将甲烷转化成CO和H₂。粉末状氧载体与甲烷反应活性较高,但其存在高含量的表面氧,易导致甲烷的完全氧化。整体型氧载体上体相晶格氧占据优势,可将甲烷选择性氧化为CO和H₂。氧化还原循环实验表明,粉末状氧载体在还原反应发生短时间内容易引起甲烷裂解导致产物气中的H₂/CO物质的量比显著大于2.0,同时产生大量积炭,制约了其循环性能。而整体型氧载体经10次循环实验后,全程反应过程中合成气H₂/CO物质的量比一直维持在2.0附近,显示了较高的循环稳定性能。     

Crystal Structure and Property of Perovskite-Type Oxides Containing Ion Vacancy

Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K₂NiF₄ compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr₂(Sr_1-xM_x)TaO_6-d (M = Ca²⁺ and Nd³⁺) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr_2-xLa_xCo_1-yTa_1+yO₆ and oxygen-deficient Sr_2-xLa_xMg_1-yTa_1+yO_6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size.     

Synthesis, hydrothermal stability and thermal reaction behavior of nepheline hydrate i (NH I)

Summary The activity of Pt/Ce_1-xGd_xO_2-y samples in steam and dry reforming of methane at short contact times correlates with the lattice oxygen mobility. For the partial oxidation of methane (POM), the oxygen mobility should be optimized to prevent methane combustion.     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

The oxidation of carbon monoxide on iron oxide

The oxidation of CO on α-Fe₂O₃ was studied in a flow reactor. The conversion was complete at 650–660 K. The catalytic activity of iron oxide was higher than that of the ferrite-containing xMgOyFe₂O₃ catalyst. The adsorption of CO on iron oxide and the kinetics of interaction of carbon monoxide with oxygen atomically adsorbed on the surface of α-Fe₂O₃ were studied. The kinetic parameters of the oxidation of CO are evidence of the participation of adsorbed oxygen atoms, whose binding energy on the surface of α-Fe₂O₃ is lower than that on the surface of the magnesium ferrite-containing catalyst.     

溶胶-凝胶法制备NixCo1-xCoAlO4尖晶石型复合氧化物及其催化分解N2O性能

用溶胶凝胶法制备了一组Ni_xCo_1-xCoAlO₄尖晶石型复合氧化物,并采用表面润湿浸渍K₂CO₃溶液进行了K掺杂改性,用于有氧气氛下的N₂O催化分解反应.采用N₂物理吸附、X-射线衍射(XRD)、扫描电镜(SEM)、H₂-程序升温还原(H₂-TPR)等技术对催化剂进行了表征,考察了催化剂组成、母液pH值、K负载量等制备参数对其催化活性的影响.结果表明,母液pH值为3、K/(Ni+Co)物质的量比为0.1的K/Ni_0.15Co_0.85CoAlO₄催化剂具有较高的N₂O分解活性,450 ℃ N₂O可完全分解.助剂K的加入弱化了催化剂表面金属氧键,提高了催化剂的还原性、催化活性和抗水性.     

Partial Oxidation of Methane to Syngas Using Lattice Oxygen of La1-xSrxFeO3

Catalytic partial oxidation of methane to syngas using the lattice oxygen of La1-xSrxFeO3 perovskite oxide catalysts in place of molecular oxygen was studied. La1-xSrxFeO3 (x＝0, 0.1, 0.2,0.5) perovskite oxides were prepared by the "auto-combustion method". XRD analysis showed that all La1-xSrxFeO3 samples have a single-phase perovskite-type oxide. The redox properties of the catalysts were investigated by temperature programmed reduction with hydrogen (H2-TPR). Reducibility of the catalysts increase with the increasing of the Sr2+ content. The oxygen species of the catalysts and their reaction with CH4 were studied by the temperature programmed surface reaction (CH4-TPSR). In the absence of gas phase oxygen, there exist two kinds of oxygen species on the catalysts. One kind of the oxygen species with strong oxidative ability is produced first, which can oxidize CH4 completely to CO2 and H2O.Then, the second oxygen species with weak oxidative ability is formed, which can oxidize CH4 partially to CO and H2 with high selectivity. The number of the oxygen species with strong oxidative ability in the CH4-TPSR tends to become zero at low x values (x≤0.1). Under suitable reaction conditions, switching alternatively the reactions of 11% O2-Ar and 11% CH4-He over a La0.sSr0.2FeO3 catalyst at 900 ℃ allows methane to be selectively converted to synthesis gas (CH4 conversion ～90%, CO selectivity ＞93%) using the lattice oxygen of the perovskite oxide catalyst in a redox mode.