Catalytic oxidation of methane over Pd/Co3O4

The catalytic activity of Pd/Co₃O₄ toward methane oxidation has been examined in this study as a function of Pd loading, reaction temperature, space velocity and methane concentration in the reaction gas mixture. The bare oxide is quite active achieving a 100% methane conversion at 480°C under the reaction conditions used. The catalyst with the highest Pd loading tested of 10 wt.% yields the best activity curve, but the 5 wt.% Pd/Co₃O₄ catalyst performs nearly as well. Complete conversion for this catalyst is attained at 300°C and the activity remains stable over a 90-min test period.     

Influence of Pt and Pd on the catalytic activity of tungsten and molybdenum oxides in the deep oxidation of methane

It has been shown that the phases H_xMO₃ and MO_3−x (M = Mo, W), obtained by reduction of the oxides WO₃ and MoO₃ with hydrogen with supported Pt(Pd) (0.5 mass %), have higher catalytic activity in the deep oxidation of methane than the catalysts Pt/Al₂O₃ and Pd/Al₂O₃ with the same amount of supported metal. At temperatures above 700 K the activity of these catalysts decreases in consequence of the thermal decomposition of the phases H_xMO₃ and MO_3−x and they become similar in activity with Pt(Pd)/Al₂O₃. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 126–129, March–April, 2008.     

Catalytic properties of Ni/ceria-yttria electrode materials for partial oxidation of methane

The catalytic properties of electrode materials Ni/Ce1-xYxO2-δ (x = 0.05, 0.10, 0.15 and 0.20) were investigated for partial oxidation of methane (POM). The CeO2-Y2O3 solid solutions were prepared by co-precipitaion method. The Ni-based catalysts supported on the solid solutions were obtained using the impregnation method. Structural, surface and redox characteristics of the prepared catalysts were systematically examined by means of X-ray diffraction (XRD), N2 adsorption-desorption (Brunauer-Emmet-Teller BET method), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) methods. The results indicated that yttria doped in the ceria system, forming a good solid solution, readily induced more defects and oxygen vacancies that favored the improvement of catalytic activity and coking resistance. In the temperature range of 600-850 ℃, Ni/Ce0.90Y0.10O1.95 catalyst exhibited the best catalytic activity among the four tested catalysts, with the CH4 conversion, CO selectivity and H2 selectivity of 78.8%, 90.6% and 89.8%, respectively, at 850 ℃. And the H2/CO molar ratio in products of Ni/Ce0.90Y0.10O1.95 catalyst was closer to the theoretical value of 2.0. The excellent coking resistant behaviors for all catalysts were clearly manifested by Thermal Analysis.     

Partial oxidation of methane and ethane to oxygenates over silica supported rhenium oxide

Silica supported rhenium oxide has been studied for partial oxidation of methane and ethane with oxygen. Loading of rhenium oxide on silica remarkably increases the conversions of methane and ethane. The presence of rhenium oxide increases the selectivity to useful oxygenates, particularly in ethane oxidation. The results suggest that rhenium oxide not only activates methane or ethane but also enhances oxygen transfer to form oxygenates. This revised version was published online in June 2006 with corrections to the Cover Date.     

氟修饰的含Ni类水滑石在甲烷部分氧化制合成气中的应用研究

通过共沉淀法合成了含Ni/Mg/Al的类水滑石,并利用水滑石的"重构性能"将F^-引入到水滑石层间。焙烧该类水滑石后得到Ni/Mg/Al/O-F催化剂,采用XRD、SEM、CO₂-TPD、H₂-TPR、N₂吸附-脱附等手段对其结构进行了表征。结果表明,焙烧后的催化剂为方镁石结构,并具有丰富的介孔,Ni/Mg/Al/O-F较之不含F^-的复合氧化物Ni/Mg/AlO具有更小的比表面积、颗粒粒径和结晶度,但是碱密度明显增大,并且在甲烷部分氧化(POM)反应中表现出更高的活性和稳定性,反应120h后,活性没有下降。这是因为F^-的引入提高了催化剂碱性和活性组分Ni的分散,从而改善了催化剂的抗积炭和烧结能力。     

Formation of pure hydrogen from methane

The methods for production of pure hydrogen from methane are summarized. One method is methane decomposition to hydrogen and carbon nanofibers. Ni-based catalysts with high activity and long life for the methane decomposition were developed. The other method is based on the redox of iron oxides, i.e., Fe₃O₄ is reduced with methane to iron metals and, subsequently, iron metals are oxidized with water vapor to form hydrogen. Iron oxide mediators that could be reduced with methane and subsequently be oxidized with water vapor at low temperatures were designed.     

Effect of preparation of Ag/Co composite oxide on characteristic and activity for carbon monoxide oxidation

We report our results on the development of 1:1 in molar Ag/Co composite oxide prepared by co-precipitation, and the effect of different rates of precipitation and heat treatment on the surface area, pore size and also catalytic activity for CO oxidation. It was observed that slow precipitation of the catalysts gave small pore sizes, high surface area and high activity for CO oxidation at low calcination temperatures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of support and loading on oxidation of methane over platinum catalysts

Catalytic combustion of methane was carried out using platinum catalysts supported on low-and high-surface area alumina (denoted respectively as LSA and HSA) and platinum supported on silica. Methane conversion was the highest for platinum supported on LSA alumina, smaller for Pt/HSA alumina and the smallest for Pt/silica. However, the 3 wt.% Pt/HSA catalyst was found to show the highest selectivity.     

Effect of nitrogen oxides NOx on gas-phase oxidation of methane by oxygen

We propose a kinetic model for gas-phase oxidation of methane by oxygen in the presence of nitrogen oxides NOx. The model calculations agree satisfactorily with experimental kinetic data provided in the literature. We consider the basic principles for the effect of nitrogen oxides on the rate of the process and the selectivity with respect to methanol and formaldehyde. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 113–118, March–April, 2006.     

氮掺杂氧化石墨催化苄胺氧化

酰胺类化合物是重要的化工原料和生物医药合成的中间体,但其制备大部分需要使用贵金属催化剂,因此,发展廉价金属乃至非金属催化剂具有重大意义.本文使用化学气相沉积法合成了氮掺杂的层状氧化石墨材料,并将其应用于苄胺氧化反应中,实现了液相中酰胺合成的非金属催化过程.在水相中可以活化氧气较高产率地生成亚胺化合物N-苄亚甲基苄胺,并且成功实现了在氨水反应介质中高转化率和选择性地生成苯甲酰胺.此外,对反应中的影响因素进行了逐一研究,并从多方面探究了该反应中氨水的作用以及反应最可能的历程,提出了一条经过包括亚胺在内的多个中间产物的反应路径.本工作对于研究碳氢键的活化过程以及拓宽碳催化领域进行了有益的尝试.     

Selective methane oxidation to formaldehyde using polymorphic T-, M-, and H-forms of niobium(V) oxide as catalysts

The investigations of selective methane oxidation to formaldehyde over T-Nb₂O₅, the mixture of M-Nb₂O₅ and H-Nb₂O₅ as well as H-Nb₂O₅ were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as the oxidizing agent. T-Nb₂O₅ samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h⁻¹). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb₂O₅ displayed various formaldehyde and carbon dioxide yield. Using H-Nb₂O₅ and M-Nb₂O₅ phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb₂O₅ (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb₂O₅ supported on SiO₂. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Promoting effect of tin oxide on the activity of silica- supported gold catalysts used in CO oxidation

In this study various Au/SnO_x-SiO₂ catalysts were prepared and tested in CO oxidation. It was found that the addition of tin oxide onto silica increased significantly the activity of Au/SiO₂ catalysts due to the alteration of the nanoenvironment of gold, which was evidenced by XPS and FTIR measurements.     

不同载体Ni基负载型催化剂对甲烷部分氧化制合成气催化行为研究

采用浸渍法制备了单一载体(Al₂O₃、ZrO₂、CeO₂)和ZrO₂、CeO₂改性的Al₂O₃复合载体的Ni催化剂,考察了在甲烷部分氧化制备合成气反应中的催化性能。通过N₂-物理吸附、H₂程序升温还原、X射线衍射、NH₃程序升温脱附和程序升温氧化等技术对催化剂进行了表征。结果表明,在单一载体催化剂中,Ni/Al₂O₃具有较大的比表面积,其初始反应活性较高,但该催化剂表面易形成大量的积炭而快速失活。Ni/ZrO₂和Ni/CeO₂催化剂比表面积较小,活性金属Ni在其表面分散性差,催化剂具有较低的CH₄转化率。而CeO₂和ZrO₂改性的Al₂O₃复合载体催化剂,具有较大的比表面积,反应活性明显高于单一载体催化剂。CeO₂-Al₂O₃复合载体催化剂具有最高的反应活性和较好的反应稳定性。同时表明,含CeO₂催化剂反应后表面积炭较少,CeO₂的储放氧功能增强了催化剂对O₂的活化,提高催化剂活性的同时,可以抑制积炭的生成。     

碱土Sr对Co/Al2O3催化剂甲烷部分氧化反应的影响

以γ-Al₂O₃为载体,采用共浸渍法制备了Sr-Co/Al₂O₃系列催化剂,研究了助剂Sr对Co/Al₂O₃催化剂上甲烷部分氧化(POM)制合成气反应的影响,并利用N₂物理吸附、X射线衍射、H₂-程序升温还原和热重等技术对催化剂的理化性质进行了表征。结果表明,未添加助剂的Co/Al₂O₃和800℃焙烧的Sr-Co/Al₂O₃催化剂在POM反应初期催化活性很低,然而,当添加Sr的质量分数高于2%时,催化剂表现出很好的催化活性和稳定性。焙烧后的新鲜催化剂上主要存在两类Co物种,一类是与载体相互作用较弱、易被H₂还原为单质的Co₃O₄;另一类是与载体相互作用较强、难还原、无催化活性的CoAl₂O₄尖晶石。在焙烧过程中,Sr易形成Sr₄Al₁₄O₂₅,从而削弱Co与Al₂O₃之间的相互作用,能在一定程度上抑制CoAl₂O₄物种的形成,提高催化剂的稳定性和活性。未添加Sr的Co/Al₂O₃在反应时易发生物相改变生成尖晶石,导致催化剂迅速失活;但当焙烧温度达到800℃时,添加有限量的Sr还是无法阻止CoAl₂O₄的产生。     

Nanosized rhodium oxide for water oxidation: An organometallic precursor for the preparation of rhodium oxide

Electrochemical production of hydrogen from water splitting is a promising process to allow storage of intermittent energies. However, anodic water oxidation, which is a complicated four‐proton, four‐electron transfer process, affects the efficiency of hydrogen generation due to the need to apply large overpotentials. Herein, we synthesized nanosized rhodium(III) oxide by the thermal decomposition of a known rhodium organometallic precursor and characterized it using scanning and transmission electron microscopies, powder X‐ray diffraction, energy‐dispersive X‐ray, diffuse reflectance infrared and Fourier transform infrared spectroscopies, and electrochemical methods. The results showed that the nanosized rhodium oxide is a promising catalyst for water oxidation.     

Catalytic oxidation of methane at low temperature over Pd-containing perovskite type oxides

Two types of catalysts with the same palladium loading, palladium-substituted perovskite La_0.95Ce_0.05Co_0.95Pd_0.05O₃ and perovskite-supported palladium catalyst Pd/La_0.95Ce_0.05CoO₃ were prepared by the combustion and impregnation method, respectively. The catalyst structure was characterized by X-ray diffraction (XRD), BET measurements, temperature-programmed reduction (TPR) and the methane oxidation activity of the catalysts were investigated in detail. It was found that the activity performance of Pd/La_0.95Ce_0.05CoO₃ was higher than that of La_0.95Ce_0.05Co_0.95Pd_0.05O₃, and this was owing to the ease of reduction of palladium in the former.     

Catalytic activity of a nickel on alumina catalyst in the CO2 reforming of methane

The kinetics of the CO₂-reforming of methane over a stable Ni/γ-Al₂O₃ catalyst has been studied in the range of 773-873 K, at normal pressure and various CO₂/CH₄ molar ratios. An Eley-Rideal type model gives good agreement with the experimental observations and the kinetic parameters are statistically significant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heterogeneous Catalytic Partial Oxidation of C3-C4 Alkanes with Nitrogen Monoxide

The possibility of making products of partial oxidation, alcohols and acids in particular, by the reaction of C₃-C₄ alkanes with nitrogen monoxide over oxide and zeolite catalysts is demonstrated. The most effective catalysts are CeO₂ and Fe-TsVK. The dependence of the rate and selectivity of the process on the reaction conditions has been established.     

Control of the directions of oxidative transformation of methane over nickel-based catalysts by acid-base properties

Two completely different directions of the oxidative transformation of methane (OTM) were performed on nickel-based catalysts due to the different acid-base properties of those catalysts. The relatively acidic LaNiO_x and LiNiLaO_x/Al₂O₃ catalysts exhibit excellent Partial Oxidation of Methane to Syngas (POM) performance. However, the relatively basic LiNiLaO_x catalyst has a good Oxidative Coupling of Methane to C₂ Hydrocarbons (OCM) activity. The basic properties of the catalyst makes it difficult to reduce nickel and keeps it in the oxidized state. Reduced nickel is necessary for POM and oxidized nickel for the OCM reaction.