LaMnO3 Perovskite Supported Noble Metal Catalysts for the Total Oxidation of Methane

Two series of LaMnO₃ supported noble metal (Pt, Pd, Rh) catalysts prepared by the citrate method and calcined in air at 600 and 800 °C, respectively, were investigated. The catalysts resulting from method A were prepared by simultaneous incorporation of the noble metals during perovskite preparation and those following method B were generated by impregnation of the calcined perovskites with the noble metal compounds. The noble metals form solid solutions with the perovskite lattice. Reduction of the catalysts with hydrogen prior to the catalytic reaction led to a significant enhancement of the catalytic activity. During the catalytic reaction, the noble metal clusters are partially transformed to highly dispersed noble metal oxides or nonstoichiometric noble metal oxide phases, which are the catalytically active phases for the total oxidation of methane. The best results were obtained with the Pd containing catalysts prepared by method B.     

Supported Nano-Gold Catalysts for Epoxidation of Styrene and Oxidation of Benzyl Alcohol to Benzaldehyde

Nano-gold particles supported on different alkaline earth oxides (viz. MgO, CaO, BaO and SrO), Gr. IIIa metal oxides (viz. Al₂O_3, Ga₂O_3, In₂O₃ and Tl₂O₃), transition metal oxides (viz. TiO_2, Cr₂O_3, MnO_2, Fe₂O_3, CoO_x, NiO, CuO, ZnO, Y₂O₃ and ZrO₂), rare earth metal oxides (viz. La₂O_3, Ce₂O_3, Nd₂O_3, Sm₂O_3, Eu₂O_3, Tb₂O_3, Er₂O₃ and Yb₂O₃) and U₃O₈ [all prepared by depositing gold on corresponding metal oxide support by deposition precipitation (DP) and/or homogeneous deposition precipitation (HDP) method] were evaluated for their catalytic performance in the liquid phase epoxidation of styrene by tert-butyl hydroperoxide (TBHP) to styrene oxide and also in the solvent-free benzyl alcohol-to-benzaldehyde oxidation (by molecular oxygen or TBHP) reactions. For the epoxidation, the catalytic performance (styrene oxide yield) of the most promising nano-gold catalysts prepared by the HDP method was in the following order: Au/MgO > Au/Tl₂O₃ > Au/Yb₂O₃ > Au/Tb₂O₃ > Au/CaO (or TiO₂). However, for the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen, the order of choice for the most promising catalysts (based on benzaldehyde yield) was Au/U₃O₈ > Au/Al₂O₃ > Au/ZrO₂ > Au/MgO. Whereas, when TBHP was used as an oxidizing agent for the benzyl alcohol oxidation, the order of choice for the most promising catalysts was Au/U₃O₈ > Au/MgO > Au/TiO₂ > Au/ZrO₂ > Au/Al₂O₃. The catalytic performance of a particular supported nano-gold catalyst was thus found to depend on the reaction catalysed by them. Moreover, it is strongly influenced by a number of catalyst parameters, such as the metal oxide support, the method of gold depositon on the support, the gold loading and also on the catalyst calcination temperature. Nano-gold particles-support interactions seem to play an important role in controlling the deposition of gold (amount of gold deposited and size and morphology of gold particles), formation of different surface gold species (Au⁰, Au¹⁺ and Au³⁺) and electronic properties of gold particles and, consequently, control the catalytic performance (both the activity and selectivity) of the supported nano-gold catalysts in the reactions. The nano-gold catalysts prepared by the HDP method showed much better catalytic performance than those prepared by the DP, coprecipitation or impregnation method; in general, the HDP method provided supported gold catalysts with much higher gold loading and/or smaller size gold particles than that achieved by the DP and other methods.     

Hydrogen Tungsten Bronze‐Supported Platinum as Electrocatalyst for Methanol Oxidation

Hydrogen tungsten bronze (H_xWO₃)‐supported platinum was prepared by electrodeposition and used as an electrocatalyst for methanol oxidation. The prepared electrocatalyst was characterized by Raman spectrum, X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), cyclic voltammetry (CV), and chronoamperometry (CA). It is found that the support, H_xWO₃, not only reduces the platinum particle size and thus reduces the platinum loading, but also provides platinum with the anti‐poison ability to carbon monoxide and thus improves the activity of platinum toward methanol oxidation.     

金属氧化物催化剂上H_2S选择性催化氧化研究进展

选择性催化氧化法作为一种新型的脱除H_2S尾气技术,重点是开发具有高活性和多种性能特点的催化剂形成系列产品。总结了金属氧化物催化剂上H_2S选择性催化氧化反应的研究进展。重点介绍了不同载体、活性组分和助剂对催化剂活性的影响;阐述了H_2S选择性催化氧化的反应机理和失活机理,并对金属氧化物催化剂的未来发展方向上进行了展望。     

Oxidation of SO2over Supported Metal Oxide Catalysts

A systematic catalytic investigation of the sulfur dioxide oxidation reactivity of several binary (M_xO_y/TiO₂) and ternary (V₂O₅/M_xO_y/TiO₂) supported metal oxide catalysts was conducted. Raman spectroscopy characterization of the supported metal oxide catalysts revealed that the metal oxide components were essentially 100% dispersed as surface metal oxide species. Isolated fourfold coordinated metal oxide surface species are present for most oxides tested at low coverages, whereas at surface coverages approaching monolayer polymerized surface metal oxide species with sixfold coordination are present for some of the oxides. The sulfur dioxide oxidation turnover frequencies (SO₂molecules converted per surface redox site per second) of the binary catalysts were all within an order of magnitude (V₂O₅/TiO₂>Fe₂O₃/TiO₂>Re₂O₇/TiO₂∼CrO₃/TiO₂∼Nb₂O₅/TiO₂>MoO₃/TiO₂∼WO₃/TiO₂). An exception was the K₂O/TiO₂catalyst system, which is inactive for sulfur dioxide oxidation under the chosen reaction conditions. With the exception of K₂O, all of the surface metal oxide species present in the ternary catalysts (i.e., oxides of V, Fe, Re, Cr, Nb, Mo, and W) can undergo redox cycles and oxidize sulfur dioxide to sulfur trioxide. The turnover frequency for SO₂oxidation over all of these catalysts is approximately the same at both low and high surface coverages, despite structural differences in the surface metal oxide overlayers. This indicates that the mechanism of sulfur dioxide oxidation is not sensitive to the coordination of the surface metal oxide species. A comparison of the activities of the ternary catalysts with the corresponding binary catalysts suggests that the surface vanadium oxide and the additive surface oxide redox sites act independently without synergistic interactions: the sum of the individual activities of the binary catalysts quantitatively correspond to the activity of the corresponding ternary catalyst. The V₂O₅/K₂O/TiO₂catalyst showed a dramatic reduction in catalytic activity in comparison to the unpromoted V₂O₅/TiO₂catalyst. The ability of potassium oxide to significantly retard the redox potential of the surface vanadia species is primarily responsible for the lower catalytic reactivity.     

Synthesis and Characterization of Manganese Oxide Catalysts for the Total Oxidation of Ethyl Acetate

Manganese oxide catalysts were synthesized by direct reaction between manganese acetate and permanganate ions, under acidic and reflux conditions. Parameters such as pH (2.0–4.5) and template cation (Na⁺, K⁺ and Cs⁺) were studied. A pure cryptomelane-type manganese oxide was synthesized under specific conditions, and it was found that the template cation plays an important role on the formation of this kind of structure. Cryptomelane was found to be a very active oxidation catalyst, converting ethyl acetate into CO₂ at low temperatures (220 °C). This catalyst is very stable at least during 90 h of reaction and its performance is not significantly affected by the presence of water vapour or CO₂ in the feed stream. The catalyst performance can be improved by the presence of small amounts of Mn₃O₄.     

堇青石负载非贵金属复合氧化物催化氧化甲苯的性能研究

本文采用浸渍法制备了以MOx(M为Cu、Co、Zn、Fe、Ce)和Mn Ox混合氧化物为活性组分,堇青石蜂窝陶瓷为载体的有机废气催化燃烧催化剂,以甲苯作为探针反应物测定该类催化剂的催化燃烧活性。考察了M与Mn物质的量比等因素对甲苯催化燃烧性能的影响,深入进行了XRD、BET和SEM表征与分析。实验结果表明:Fe/Mn物质的量的比为4∶1,焙烧温度为500℃,催化剂具有最佳的催化燃烧活性。     

Catalytic Combustion of Volatile Organic Compounds on Supported Precious Metal Catalysts

Catalytic combustion of volatile organic compounds (VOCs) was investigated on supported precious metal catalysts. The activities for the combustion of methane and acetaldehyde were closely related to the reducibility of the precious metal oxides of the catalysts. On the other hand, light-off temperatures for toluene combustion on PdO/Al₂O₃, PdO/SnO₂, and PdO/CeO₂ were around 200 °C, although PdO/ZrO₂ showed a higher temperature of 240 °C. This result indicated that light-off temperatures depend on not only the catalytic activities but also the catalyst structure because of low concentration of toluene and weak interaction between catalysts and toluene. In this experiment, the PdO/SnO₂ catalyst showed highest activity for the combustion of methane and VOCs.     

Characterization and Catalytic Oxidation of Carbon Monoxide Over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (CoO_x/SiO₂, CoO_x/TiO₂ and CoO_x/Al₂O₃) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were investigated using thermogravimetry (TG), N₂-adsorption at −196 °C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy (DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al₂O₃ and TiO₂, while no conclusive evidence of any interaction was found for SiO₂. Besides the crystalline Co₃O₄ which was formed in three supported catalysts, both high-temperature phases CoAl₂O₄ and CoTiO₃ spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation also affected simultaneously. As the CoAl₂O₄ and CoTiO₃ spinel formed, both the surface area and catalytic activity decreased significantly.     

Anodic Alumina Supported Pt Catalyst for Total Oxidation of Trace Toluene

Featuring an assembly of identical pores, through-pore anodic alumina (AAO) makes an ideal monolith-like cat-alyst support for volatile organic compound (VOC) combustion. This work employs the oxidatio...     

Unique Catalytic Activity of Platinum Eluted into Perovskite in the Solid Phase

It has been found that Pt eluted into the (La_0.7Sr_0.2Ba_0.1)ScO_3-δ perovskite oxide exhibited higher catalytic activity for CO oxidation than for H₂ oxidation under separate reaction conditions, a behaviour which differs from that of conventional Pt catalysts. The unique activity appeared when ionic Pt in the perovskite lattice was partly reduced, forming Pt nanoparticles on the surface.     

Peroxone Oxidation of Toluene and 2,4,6-Trinitrotoluene

This paper discusses oxidation of toluene and 2,4,6-trinitrotoluene (TNT) by ozone and hydrogen peroxide mixtures (known as peroxone oxidation) at 25[ddot]C. The overall reaction in alkaline solutions is first order with respect to the concentration of dissolved ozone, and is nearly independent of the pollutant concentrations. The oxidation of toluene is one-half order in hydrogen peroxide, and the rate constant changes in proportion to the hydroxyl ion concentration with an exponent of 0.67.

In the pH range of 7 to 9, the TNT destruction rate increases with the hydrogen peroxide and hydroxyl ion concentrations with exponents of 0.104 and 0.15 respectively. It is technically feasible to treat toluene and TNT contaminated waters by the peroxone oxidation process to achieve the residual level of a few parts per billion in treated waters to meet environmental requirements.     

Catalytic Liquid Phase Oxidation of Toluene to Benzoic Acid

The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4 atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157 °C, 2 h and 0.57 g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40 kJ/mol.     

金属氧化物催化合成顺丁烯二酸二异辛酯

对合成顺丁烯二酸二异辛酯进行了研究,其中包括从众多催化剂中确定ＳｎＯ为反应催化剂,确定了反应的最佳条件,即催化剂用量为醇酐总重的１．５％,醇酐摩尔比为３∶１,反应时间２ｈ,反应温度为回流温度。最后,在最佳反应条件下,顺丁烯二酸酐的转化率达９９．８％。     

负载型臭氧氧化催化剂研究进展

多相催化臭氧化技术是一种高效的污水净化技术。其中负载型臭氧氧化催化剂因其催化效果好、易分离、重复率用率高等优点而成为研究热点之一。依据不同的载体类型,将负载型臭氧氧化催化剂进行归纳分类,并综述了不同载体的催化剂在催化臭氧氧化水处理中的最新应用。     

Preservation of the Activity of Supported Gold Catalysts for CO Oxidation

Procedures leading to the preservation of activity of supported gold catalysts for CO oxidation are reviewed. The inclusion of iron as Fe(OH)₃ in preparing catalysts using tin oxide, ceria and zirconia as supports gives better activity and much improved stability with time-on-stream. In the case of Au/Fe-SnO₂ (0.5–0.9% Au), the effect is maximal with ~4% Fe. The stability of catalysts based on ceria as support is also much better when small amounts of either iron or lanthanum during preparation of the support by thermal decomposition of nitrates. Au/SnO₂ catalysts often suffer initial deactivation followed by an increase in activity with time-on-stream; a period of refrigeration (7d) induces an excellent stability at high conversion.     

Synthesis of Molybdenum Oxide Nanohybrids as Efficient Catalysts in Oxidation of Alcohols

Novel layered materials based on molybdenum oxide have been synthesized using three amino-carboxylate ligands; terephetalic acid, p-aminobezoic acid and diaminobenzene. On the basis of X-ray diffraction, scanning electron microscopy, thermogravimetry, and infrared results, the insertion of organic ligands into the interlayer space of molybdenum oxide has been proposed. Moreover, the influence of organic guests on the oxide structure and also their catalytic performance are discussed. Furthermore, fabrication of the nanostructured molybdenum oxide is achieved by calcinations of these hybrid materials at 600 °C. Somewhat oriented nanoplatelets are viewed with different catalytic activity.     

Effective Catalysts for Wet Oxidation Of Formic Acid by Oxygen and Ozone

The catalytic wet-air oxidation and catalytic ozonation of a formic acid solution have been studied at room temperature using more than 20 kinds of catalysts including Pt/C, Pt/Al₂O₃, Pd/Al₂O₃, etc. The most effective catalyst was Pt/Al₂O₃. The apparent activation energies for the catalytic wet-air oxidation and ozonation on Pt/Al₂O₃ were both about 5 kcal/mol. This fact suggests that these reactions on the catalyst were diffusion controlled, and thus, the potential of the catalyst is likely much higher.     

Total Oxidation of Chlorinated Hydrocarbons on A1–xSrxMnO3 Perovskite‐Type Oxide Catalysts – Part II: Catalytic Activity

The influence of the kind of A‐site cation in A_1–xSr_xMnO₃ perovskites (A = La, Pr, Nd, Di [didymium]) on the catalytic activity in the total oxidation of methane, chloromethane, dichloromethane, and trichloroethylene has been studied. In contrast to methane, the total oxidation of chlorinated hydrocarbons (CHC) is connected with a reversible catalyst deactivation and the formation of byproducts at low reaction temperatures. For the catalysts calcined at 600 and 800 °C, resp., the catalytic activity is determined mainly by specific surface area, amount of oxide admixtures and crystallinity of the perovskite. DiMnO₃ showed the highest and PrMnO₃ catalysts the lowest catalytic activity in the total oxidation of methane and CHC. Partial substitution of A by Sr leads to an enhancement of the catalytic activity in the total oxidation of methane, but not in the total oxidation of CHC.     

Effect of Pt Dispersion on the Catalytic Activity of Supported Pt Catalysts for Diesel Hydrocarbon Oxidation

The catalytic activity of Pt/Al₂O₃ for the total oxidation of hydrocarbon mixture of n-decane and 1-methylnaphthalene was strongly dependent on the Pt dispersion. The maximum hydrocarbon oxidation activity was achieved for Pt/Al₂O₃ with Pt dispersion (D_Pt) of 0.39. On the other hand, the activity of Pt/ZrO₂ monotonously decreased with decreasing Pt dispersion from 1.00 to 0.09. In situ FT-IR spectroscopy suggested that the presence of plural Pt species in metallic state with slight different electric state, which well catalyze the formation of acrylate species as an intermediate, is responsible for the high catalytic activity of Pt/Al₂O₃ with D_Pt = 0.39.