Selective oxidation of methane to formaldehyde and C2 hydrocarbons over double layered Sr/La2O3 and MoO3/SiO2 catalyst bed

A double layered catalyst bed of Sr/La₂O₃ followed by MoO₃/SiO₂ has been used to produce C₂ hydrocarbons and formaldehyde from a CH₄/air mixture with a formaldehyde space time yield of 187 g (kg cat)^–1 h^–1, which is significantly higher than those yields obtained with single bed catalysts or with mechanically mixed catalyst bed at ambient pressure and 630 ° C.     

Effect of carbon dioxide on the selectivities obtained during the partial oxidation of methane and ethane over Li+/MgO catalysts

AtT 650 °C carbon dioxide either formed during reaction or added to the system increases the selectivity for the desired hydrocarbon products during the oxidative coupling of methane and the oxidative dehydrogenation of ethane reaction over Li⁺/MgO catalysts. Similarly, CO₂ inhibits secondary reactions of CH₃-radicals with the surface of the Li⁺/MgO. The improved selectivities are attributed to the poisoning effect that CO₂ has on the secondary reactions of alkyl radicals with the surface.     

Pulse-MS study of the partial oxidation of methane over Ni/La2O3 catalyst

The CH₄ direct oxidation reaction was studied at 600°C by the pulse-MS transient method over the Ni/La₂O₃ catalyst. Over the freshly prepared catalyst (which contains NiO), the CO selectivity and CH₄ conversion increased and attained constant values as the number of CH₄/O₂ pulses increased. Over the reduced catalyst (containing Ni), as the number of CH₄/O₂ pulses increased, the CO selectivity and CH₄ conversion decreased before they reached the same constant values as over the fresh catalyst. The CO selectivity increased as the residence time of the reactants shortened, implying that CO was directly generated without the preformation of CO₂. The activation energies of CH₄ dehydrogenation in the presence and absence of oxygen have been calculated using the bond-order conservation Morse-potential approach. The results indicate (1) the direct dehydrogenation steps are more likely to occur; (2) the transient oxygen species adsorbed on-top of the metal atoms promote dehydrogenation; (3) the oxygen species adsorbed on bridge or hollow sites do not promote dehydrogenation.     

Hydrogenation of m‐dinitrobenzene to m‐phenylenediamine over La2O3‐promoted Ni/SiO2 catalysts

BACKGROUND: Liquid‐phase catalytic hydrogenation of m‐dinitrobenzene is an environmentally friendly routine for m‐phenylenediamine production. The key to increasing product yield is to develop catalysts with high catalytic performance. In this work, La₂O₃‐modified Ni/SiO₂ catalysts were prepared and applied to the hydrogenation of m‐dinitrobenzene to m‐phenylenediamine. The effect of La₂O₃ loading on the properties of Ni/SiO₂ was investigated. The reaction kinetic study was performed in ethanol over Ni/3%La₂O₃–SiO₂ catalyst, in order to clarify the reaction mechanism of m‐dinitrobenzene hydrogenation. RESULTS: It was found that the activity of the silica supported nickel catalysts is obviously influenced by La₂O₃ loading. Ni/3%La₂O₃–SiO₂ catalyst exhibits high activity owing to its well dispersed nickel species, with conversion of m‐dinitrobenzene and yield of m‐phenylenediamine up to 97.1% and 94%, respectively. The results also show that Ni/3%La₂O₃–SiO₂ catalyst can be reused at least six times without significant loss of activity. CONCLUSION: La₂O₃ shows strong promotion of the effect of Ni/SiO₂ catalyst for liquid‐phase hydrogenation of m‐dinitrobenzene. La₂O₃ loading can affect the properties of Ni/SiO₂ catalyst. Based on the study of m‐dinitrobenzene hydrogenation kinetics over Ni/3%La₂O₃–SiO₂ catalyst, a possible reaction mechanism is proposed. Copyright © 2009 Society of Chemical Industry     

The effect of La2O3 on dynamic OSC over the Pd/OSC/Al2O3-based catalysts

In this study, fresh and aged Pd/(OSC–Al₂O₃) and Pd/(Al₂O₃–OSC–La₂O₃) metallic monoliths (OSC material Ce_0.75Zr_0.25O₂) were used to find out the effect of La₂O₃ on the catalyst behaviour in dynamic oxygen storage capacity (OSC) measurements. In addition, the interaction of CO, NO and O₂ reaction compounds over the studied catalysts was investigated in order to understand the effect of La₂O₃ in the oxidation and reduction reactions in lean automotive exhaust gas conditions. A FT-IR gas analyser was used to analyse the product gas composition. The presence of La₂O₃ on fresh and aged catalysts had negative effect on both the dynamic OSC and the activity of the catalyst. The reason for this is the different washcoat compositions between the studied catalysts which could explain the differences in BET surface areas.     

含Nb2O5和La2O3系统玻璃形成区

用新的玻璃形成区探索方法研究了Ｌａ２Ｏ３的质量分数分别为１％,５％,１０％时含Ｎｂ２Ｏ５,Ｌａ２Ｏ３系统玻璃的形成区（玻璃生成体分别为Ｐ２Ｏ５,ＳｉＯ２,Ｂ２Ｏ３,ＴｅＯ２＋ＧｅＯ２,修饰体为ＢａＯ,ＺｎＯ）,这些系统可作为激光激活离子Ｎｄ＾３＋,Ｙｂ＾３＋,Ｈｏ＾３＋,Ｔｍ＾３＋,Ｅｒ＾３＋等掺杂的理想基质。     

Thermal Expansion Behavior of Titanium-Doped La(Sr)CrO3 Solid Oxide Fuel Cell Interconnects

La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ shows a single phase with a hexagonal unit cell of a = 5.459(1) Å, c = 13.507(2) Å, Z = 6 and a space group of R -3 C . Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10⁻⁶/°C in air, 10.5 × 10⁻⁶/°C under a He–H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁵ atm at 1000°C), and 10.9 × 10⁻⁶/°C in a H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁹ atm at 1000°C). La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect.     

己二酸锌钙皂纳米氧化铈/氧化镧对PVC/ASA的热稳定作用

合成了己二酸锌钙皂,并将纳米氧化铈和氧化镧分别作为共稳定剂制备了新型复合热稳定剂。采用刚果红法、热失重分析仪、动态力学分析仪等考查了复合热稳定剂对聚氯乙烯/丙烯酸酯苯乙烯丙烯腈接枝共聚物（PVC/ASA）共混材料的热稳定效果及动态力学性能。结果表明,稀土化合物作为共稳定剂可以提高己二酸锌钙皂对PVC/ASA共混材料的热稳定效果,氧化镧与己二酸锌钙皂的协同效果优于纳米氧化铈,而纳米氧化铈的加入可以提高材料的热变形温度。     

Selective oxidation of methane to CO and H2 over unreduced NiO-rare earth oxide catalysts

NiO-LnO _x (Ln = lanthanide) catalysts (with NiLn=11) without prereduction show high activity/selectivity and very high productivity in the oxidative conversion of methane to CO and H₂. The catalysts are first activated in the initial reaction, which is started at 535–560°C, by the reduction of NiO and creation of active sites. The carbon deposition on the catalysts in the reaction, particularly for the NiO-Gd₂O₃, NiO-Tb₄O₇ and NiO-Dy₂O₃ catalysts, is quite fast but it has caused a little or no influence on the catalytic activity/selectivity. Pulse reaction of pure methane on NiO-Nd₂O₃ (at 600°C) shows involvement of lattice oxygen in the initial reaction and also reveals formation of carbon from CO on the catalyst reduced in the reaction.     

Partial oxidation of methane with N2O over Fe2(MoO4)3 catalyst

The product distributions for partial oxidation of methane on Fe₂(MoO₄)₃ catalyst were changed remarkably when the oxidant was switched from oxygen to nitrous oxide. When oxygen was used as the oxidant, the main products were HCHO and CO. However, when nitrous oxide was used, the formation of HCHO was greatly suppressed and C₂ hydrocarbons (C₂H₆ and C₂H₄) were newly produced. The difference in kinetic behaviors between the two reactions using nitrous oxide and oxygen as the oxidant can be explained in terms of the competitive conversions of methyl intermediate into HCHO and C₂H₆. In the case of nitrous oxide as the oxidant, the adsorbed methyl intermediate would be transformed predominantly into C₂H₆ due to a low steady-state concentration of the active oxygen species on Fe₂(MoO₄)₃.     

CO preferential oxidation over Au/MnOx-CeO2 catalysts prepared with ultrasonic assistance: Effect of calcination temperature

The Au/MnO_x-CeO₂ catalysts used for CO preferential oxidation were prepared by deposition-precipitation with ultrasonic assistance. The effect of calcination temperature (150-350 °C) on the structures and catalytic performance of the catalysts was systematically investigated. It is found that the catalyst Au/MnO_x-CeO₂ calcined at 250 °C exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest selectivity of oxygen to CO₂ at 120 °C. The results of XRD, TEM and XPS indicate that this catalyst possesses the smallest particle size, the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which are favorable to CO oxidation. The H₂-TPR results reveal that the selectivity of oxygen to CO₂ is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the support in Au/MnO_x-CeO₂-250 decreases its capability for H₂ dissociation and oxidation, leading to high selectivity of oxygen to CO₂.     

Methane oxidation over vanadium-modified Pd/Al2O3 catalysts

Three different vanadium-modified Pd/Al₂O₃ catalysts were prepared and tested as catalysts for the deep oxidation of methane. Vanadium was added to the palladium catalyst by incipient wetness of palladium catalyst in order to modify its properties and improve its thermal stability and thioresistance. The behaviour of vanadium-modified catalysts depends on the concentration of this compound, being 0.5 wt.% the optimum amount. However, when strong catalyst poisons are present in the gas (SO₂), these modified catalysts do not show a better performance than unmodified catalyst. Bimetallic catalysts were tested with and without further reduction, being observed that reduced bimetallic catalysts perform worse than the non-reduced ones.     

羧酸离子液体/氧气催化氧化芳甲醇

在组合体系“1-乙基-3-甲基咪唑乙酸盐（[EMIm][OAc]）/O2”作用下,以芳甲醇为原料,经氧化反应,合成了系列芳甲醛（酮）类化合物。通过对条件进行优化,得到适宜反应条件为：芳甲醇与1-乙基-3-甲基咪唑乙酸盐物质量比为1 : 1,氧气压力为0.2 MPa,温度为130 ℃,时间为12 h。在此条件下,实现了苯甲醛克级规模制备,得到20种芳甲醛（酮）,产率为65%~96%。根据研究结果与相关文献报道,提出了[EMIm][OAc]通过阴离子作用于苯甲醇,经O2氧化,脱水得到苯甲醛的反应机理。     

Partial oxidation of methane over Y1Ba2Cu3O6+X−ZFZ

In this communication we report our study on using high-temperature superconductors as partial oxidation catalysts. We have also investigated fluorinated superconducting materials, since the presence of a strong oxidizing agent should favor partial oxidation selectivities.     

Oxidative coupling of methane over LaF3/La2O3 catalysts

We studied the oxidative coupling of methane over the LaF₃/La₂O₃ (5050) catalyst. The catalyst was found active even at 873 K. At 1023 K, the C₂ yield was 12.7% at 26.0% CH₄ conversion and 49.1% C₂ selectivity. It was found to be stable and had a lifetime not less than 50 h at 1023 K. The catalyst was effective in C₂H₆ conversion to C₂H₄. XRD results indicated that the catalyst was mainly rhombohedral LaOF. It is suggested that the catalyst has ample stoichiometric defects and generates active oxygen sites suitable for methane dehydrogenation.     

Transient experiments on the selective oxidation of methane to formaldehyde over V2O5/SiO2 studied in the temporal-analysis-of-products reactor

Methane oxidation to formaldehyde was studied over a vanadium oxide catalyst supported on silica at 630 °C using the technique known as temporal analysis of products with sequential pulsing of methane and oxygen. This work shows that methane interacts very weakly and oxygen very strongly with the catalyst surface and it is concluded that the initial activation of methane involves an adsorbed oxygen species. Methyl radicals formed in the first step subsequently extract lattice oxygen to yield formaldehyde.     

Studies on CrO x /La2O3/ZrO2 catalysts modified by Mg

Lanthana–zirconia supported chromium oxide and magnesium chromium mixed oxide catalysts were studied in the dehydrocyclization of n-octane and characterized by temperature-programmed desorption of NH₃, temperature-programmed reduction, XPS and DRIFTS. The Mg-free catalyst shows the highest activity, but suffers from rapid deactivation due to coke formation. The addition of Mg decreases the initial activity of the supported chromium oxide and retards its deactivation. The characterization results reveal that the deactivation retarding effect of Mg species not only consists in the deletion of strong acid sites but also in the decoration and/or dilution of Cr³⁺ oxide cluster, supposedly due to the formation of Mg–Cr surface compounds and, thus, in preventing the formation of coke.     

Co/RPSA系列催化剂在N2O分解中的应用

采用正交试验设计方法设计和浸渍法制备分子筛RPSA负载Co、K、Ba和Sr催化剂,使用微型反应器评价催化剂用于直接分解N₂O的催化活性,考察活性组分对催化剂活性的影响。采用XRD、H₂-TPR和NH₃-TPD等方法对催化剂进行表征。结果表明,金属Co和K对催化剂活性影响显著,Co对提高催化剂活性有促进作用,Co含量增加,催化剂活性提高,而K对催化剂活性有抑制作用。催化剂表征结果显示,Co物种主要以Co₃O₄形式存在于载体表面,催化剂的组成和配比影响催化剂活性、氧化还原性能和酸性,催化剂强酸的存在有利于催化剂活性的提高。
     

Autothermal Methane Oxidative Coupling Process over La2O3/MgO Catalysts

Some essential conditions necessary to reach an autothermal regime in methane oxidative coupling on La₂O₃/MgO catalysts were investigated. The following three ways can be suggested to transfer the process into the autothermal regime: (1) higher initial concentrations of reagents; (2) larger reactor diameter; (3) optimization of the flow rate and the preheating temperature. It was found that the optimal temperature of the autothermal regime of methane oxidative coupling is governed by the nature of the catalyst.     

稀土La2O3添加对氧化铝多孔陶瓷性能的影响

以煅烧α-Al2O3为原料,稀土氧化镧(La2O3)为添加剂,羧甲基纤维素为成型粘结剂,通过混料、困料、研磨、模压成型、高温烧结等工序制备了氧化铝多孔陶瓷,研究了烧结温度及La2O3添加量对氧化铝多孔陶瓷的线收缩率、体积密度、孔隙率、抗折强度和微观形貌的影响。结果表明:在相同烧结温度下,随稀土添加量的增加,多孔陶瓷的体积密度、线收缩率与抗折强度均降低,而孔隙率则逐渐增加。微观形貌与X衍射分析表明,稀土La2O3的加入,抑制了氧化铝颗粒间的烧结,并在高温下与氧化铝反应生成了片状晶体LaAl11O18,片状晶LaAl11O18阻碍了氧化铝晶粒的长大,进而抑制了坯体的收缩,最终使得氧化铝多孔陶瓷具有较高的孔隙率。