天然气催化燃烧催化剂的研究(Ⅱ）

介绍了天然气催化燃烧钙钛矿型氧化物催化剂、六铝酸盐型催化剂以及负载型非贵金属催化剂的研究现状。对于钙钛矿型氧化物催化剂,利用A位取代或调整B位元素的种类及配比、新的技术和方法制备高比表面积或具有纳米结构的钙钛矿型氧化物,是提高其甲烷催化燃烧活性的重要手段。六铝酸盐型催化剂具有很高的热稳定性和甲烷燃烧活性,但起燃温度较高,通过采用将金属Pd负载到六铝酸盐上或改变制备方法,提高其比表面积,以提高其低温反应活性。负载型非贵金属催化剂研究最多的是过渡族金属,其氧化活性、抗毒性能和耐久性都存在问题,需进一步研究。     

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.     

Catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite

The catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite was investigated. The catalysts were synthesized by the impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area measurement. The effects of the mole ratio of Fe to Mn, the loading of Fe–Mn mixed oxides on the catalyst support and the calcination temperature were all investigated. The results indicate that Fe–Mn/cordierite catalysts with a 4 mol ratio of Fe to Mn, used with 10 wt% loading, and calcined at 500 ^°C showed the highest catalytic activities as measured by the oxidation of toluene. Compared to unsupported powder catalysts of Fe–Mn mixed oxides, the Fe–Mn/cordierite catalyst showed higher activity for the catalytic combustion of toluene with less active component.     

Role of potassium in the aerobic oxidation of aromatic alcohols over K+-promoted Mn/C catalysts

The aerobic oxidation of aromatic alcohol on alkali metal promoted Mn/C catalysts has been investigated. A dramatic improvement of the oxidation activity can be observed when the Mn/C catalyst is modified with potassium ions. Characterizations of Raman and X-ray absorption fine structure (XAFS) evidence that potassium ions induce a large local distortion to Mn–O octahedrons in supported manganese oxides with coexistence of Mn²⁺ and Mn³⁺, which has been suggested to be a vital factor to enhance the activation of O₂ for the oxidation of benzylic alcohol.     

The Stability Study of Au/La-Co–O Catalysts for CO Oxidation

Perovskite oxide LaCoO₃ and the mixture oxides of La₂O₃ + Co₃O₄ were prepared by sol–gel method. Then Au/La–Co–O catalysts were prepared by deposition- precipitation (DP) method and characterized by means of XRD, BET, XPS, TEM and IR. The catalytic performance for CO low-temperature oxidation and stability over these catalysts were compared. The results of experiment showed gold catalysts supported on perovskite oxides have higher catalytic activity and stability than that of supported on the simple oxides.     

挥发性有机物燃烧催化剂的研究进展

挥发性有机物（VOCs）是主要大气污染物质,也是形成PM_2.5和臭氧的重要前体。强化挥发性有机物控制,是改善大气环境的重要途径。催化燃烧（氧化）被认为是去除VOCs最有效的方式之一,本文综述了VOCs催化燃烧常用的贵金属催化剂、非贵金属催化剂。其中,贵金属催化剂主要包括基于Pd、Pt、Ru等的催化剂,非贵金属催化剂主要包括Mn、Co、Ce、Zr等的氧化物,通常贵金属催化剂具有比非贵金属更高的氧化活性和稳定性,但对于含氮VOCs非贵金属催化剂（Mn、Cu）具有更好的氮气选择性,Cr基催化剂对于含氯VOCs燃烧具有更好的效果。此外,还重点讨论了载体、分散度、催化剂制备方法对贵金属催化剂性能的影响,并对发展VOCs氧化催化剂的研究提出了展望。     

5-羟甲基糠醛无碱有氧氧化合成2,5-呋喃二甲酸负载型贵金属催化剂的研究进展

将生物质平台分子5-羟甲基糠醛（5-hydroxymethylfurfural,HMF）高效、绿色地催化转化为更高附加值的2,5-呋喃二甲酸（2,5-furandicarboxylic acid,FDCA）已经成为目前生物质能源转化领域的研究热点。碱性载体负载贵金属催化剂用于HMF无碱氧化为FDCA已经得到广泛研究,并取得了一系列成果。本文综述了水滑石、羟基磷灰石、碳材料、金属氧化物等不同载体负载的贵金属催化剂用于HMF无碱氧化为FDCA的最新进展,详细介绍了各类催化剂的结构性质、催化反应参数及催化活性,重点讨论了催化剂与催化反应的构效关系及催化反应机理等研究工作。最后,指出了今后在HMF转化为FDCA的研究工作中负载型贵金属催化剂的设计开发及机理探究等方面的努力方向。     

Low temperature catalytic oxidation of nitric oxide over the Mn–CoOx catalyst modified by nonthermal plasma

Nonthermal plasma (NTP) treatment was investigated to modify the Mn–CoO_x catalyst for the low-temperature oxidation of nitric oxide. The catalysts were characterized by XRD, BET, TGA and XPS techniques. The results showed that the activity of NTP-treated catalysts improved significantly, and that NTP treatment has the advantage of changing the structural and morphological properties (higher surface areas and pore volume) and varying the relative surface concentration and oxidation states of surface species over catalysts. High surface areas and pore volume, high concentration of chemisorbed oxygen, Mn^4 + and Co^2 +, and the efficient synergetic catalytic effect between Co and Mn ions were thought to be the main reasons for the high activity of NTP-treated catalysts.     

Preparation and Application of Perovskite Catalysts for Diesel Soot Emissions Control: An Overview

The diesel engines are energy efficient (1), but their particulate matter (soot) emissions are still a matter of concern even though major advances in their control are being made. For soot abatement, catalytic diesel particulate filter (DPF) technique is widely employed to trap and burn the soot. Many types of catalysts have been investigated for the soot combustion i.e. platinum group metal (PGM) based, perovskite-type oxides, spinel-type oxides, rare earth metal oxides, and mixed transient metal oxides etc. The cost of PGM catalysts is high and their availability is questionable. Further they are susceptible to poisoning and have low thermal stability. On the other hand perovskite catalysts show potential as effective soot oxidation catalyst for the DPF because of their low cost, high thermal stability and tailoring flexibility. Many papers related to soot oxidation over perovskite catalysts have been published but no review paper appears in the literature that is dedicated to soot oxidation. Thus, this article provides a summary of published information regarding pure and substituted perovskite catalyst, preparation methods, properties, and their application for diesel soot emission control.     

Bench Scale Experiments of Diesel Soot Oxidation Using Pr0.7Sr0.2K0.1MnO3 Perovskite Type Catalyst Coated on Ceramic Foam Filters

Potassium and strontium substituted praseodymium manganate type perovskite catalyst coated on ceramic foam filters have been studied for diesel particulate removal. The synthesized catalyst coated filter pieces have been characterized by using XRD, SEM and TG analysis, whereas their catalytic activity towards soot oxidation was tested using a bench scale facility with real diesel engine exhaust. The catalyst coated filters decrease the soot oxidation T_initial value by 150 °C and T_final by 100 °C as compared to bare soot oxidation reaction, which can be considered as high activity under the actual conditions of diesel engine. The catalytic materials show good thermal stability, while their low cost will also add to their potential for practical applications. Although perovskites have been studied for laboratory evaluations of catalytic soot oxidation, present results further substantiate the possibility of using low-cost, supported, non-noble metal based catalysts for diesel exhaust emission control applications, especially for the cost-effective retrofitment of in-use vehicles with old generation engines.     

Low Cost, Ceria Promoted Perovskite Type Catalysts for Diesel Soot Oxidation

Perovskite type catalysts with SrCoO₃ and Sr_0.8Ce_0.2CoO₃ compositions have been prepared by co-precipitation and other methods and, their catalytic activity towards diesel particulate matter (PM)/carbon oxidation has been evaluated under the loose contact condition. These catalysts show excellent catalytic activity for PM/carbon oxidation, despite their low surface area and under the loose contact condition. The synergistic effects of Ce incorporation in perovskite and presence of a small amount of potassium appears to be responsible for the high soot oxidation activity of these perovskite type materials. The Ce incorporation seems to be contributing by enhancing the redox property of the catalyst, while it appears unlikely that potassium is contributing by improving the catalyst–soot contact through its volatization. The catalysts show excellent thermal stability and stable activity under repeated cycles of use.     

Total Oxidation of Hydrocarbons on Perovskite Oxides

Perovskite-type oxides containing transition metals are attracting great attention as catalysts for complete oxidation of hydrocarbons as well as electrochemical reduction of oxygen (1). A s far as I know, the use of perovskite-type oxides as catalysts was first reported by Meadowcroft in 1970 (2) for the electrochemical reduction of oxygen. Soon after that, Voorhoeve et al. (3) reported the high catalytic activity of perovskite oxides for heterogeneous oxidation. These studies triggered many studies thereafter which are related to exhaust control catalysts and electrode catalysts.     

Total Oxidation of Hydrocarbons on Perovskite Oxides

Perovskite-type oxides containing transition metals are attracting great attention as catalysts for complete oxidation of hydrocarbons as well as electrochemical reduction of oxygen (1). A s far as I know, the use of perovskite-type oxides as catalysts was first reported by Meadowcroft in 1970 (2) for the electrochemical reduction of oxygen. Soon after that, Voorhoeve et al. (3) reported the high catalytic activity of perovskite oxides for heterogeneous oxidation. These studies triggered many studies thereafter which are related to exhaust control catalysts and electrode catalysts.     

Catalytic Removal of Toluene in Air over Co–Mn–Al Nano-oxides Synthesized by Hydrotalcite Route

Co–Mn–Al hydrotalcite type solids were synthesized as precursors of catalysts for the total oxidation of toluene in air. For the as-prepared solids, XRD measurements indicate the coexistence of hydrotalcite and MnCO₃ phases. When calcination is performed at 500 °C, different mixed oxides are found as a function of Co:Mn molar ratio and preparation method, and very high specific surface areas were obtained for the Co–Mn solids. The comparison of catalytic activities in the presence of calcined hydrotalcites with those in the presence of calcined hydroxides evidences the superiority of the first oxides due to their higher reducibility. Co–Mn–Al nano-oxides synthesized using hydrotalcite type solids as precursors, are very promising candidates for the substitution of noble metal based solids.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Progress in non-precious metal oxide-based cathode for polymer electrolyte fuel cells

The cathode catalysts for polymer electrolyte fuel cells should have high stability as well as excellent catalytic activity for oxygen reduction reaction (ORR). Group 4 and 5 metal oxide-based compounds have been evaluated as a cathode from the viewpoint of their high catalytic activity and high stability. Although group 4 and 5 metal oxides have high stability even in acidic and oxidative atmosphere, they are almost insulator and have poor ORR activity because they have a large band-gap. It is necessary to modify the surface of the oxides to improve the ORR activity. We have tried the surface modification methods of oxides into four methods: (1) formation of complex oxide layer containing active sites, (2) substitutional doping of nitrogen, (3) introduction of surface oxygen defect and (4) partial oxidation of carbonitrides. These modifications were effective to improve the ORR activity of the oxides. The solubility of the oxide-based catalysts in 0.1 mol dm⁻³ at 30 °C under atmospheric condition was mostly smaller than that of platinum black, indicating that the oxide-based catalysts had sufficient stability compare to the platinum. The onset potential of various oxide-based cathodes for the ORR in 0.1 mol dm⁻³ at 30 °C achieved over 0.9 V vs. a reversible hydrogen electrode.     

A mesoporous Pt-SBA-15 nano architecture with catalytic functions on oxidation of CO

Among many kinds of noble metal catalysts, platinum is the most efficient and widely used as automotive exhaust catalysts for treatment to remove poison gases. Due to the regular pore system and controllable pore size, mesoporous silica has been acknowledged as supports of adsorption, separation, catalysts for the extremely large surface areas and shape selective properties. SBA-15 supported Pt particles are prepared by a facile method and characterized by X-ray diffraction, Transmission Electron Microscopy and N₂ isotherms techniques. Results indicate that the Pt precursor is introduced into the mesoporous successfully and all of the particles are confined in SBA-15 with monodispersed form and uniform size. The catalytic activity of Pt-SBA-15 on oxidation of carbon monoxide are also investigated and the result indicate that the catalysts possess high catalytic activity, catalytic efficiency and stability on oxidation of CO.     

含氯挥发性有机物的催化氧化研究进展

催化氧化是控制挥发性有机污染物排放的有效途径之一,但传统催化剂在氧化消除含氯挥发性有机物(CVOCs)时易中毒而失活,因此,研发新型、高效、稳定的催化剂对其工业应用具有重要意义。简要综述近年来稀土及过渡金属氧化物、分子筛和负载贵金属催化剂对CVOCs氧化的催化性能和催化反应机理,剖析CVOCs氧化反应副产物的形成和催化剂失活的原因,并展望CVOCs催化氧化技术的未来发展趋势。     

改性镧系钙钛矿催化剂强化挥发性有机物催化氧化的研究进展

钙钛矿因其结构稳定并具有优异的物化性质,近年来在催化剂方面的应用受到了广泛关注。本文综述了采用不同方法对镧系钙钛矿进行改性来增强催化剂的活性、抗毒性、稳定性和选择性的研究进展;分析了镧系钙钛矿的结构、表面参数、活性氧和低温还原性对于挥发性有机物转化效率的影响,重点阐述了通过优选钙钛矿的制备方法、制备负载型钙钛矿和掺杂型钙钛矿等改性方法来提高镧系钙钛矿催化剂的性能,由此展望了未来改性镧系钙钛矿催化剂的研究方向：采用非金属元素掺杂或多种强化方法结合制备高效催化剂、利用催化燃烧协同光催化氧化转化挥发性有机物、进一步通过实验和仿真模拟制备理想钙钛矿催化剂催化氧化多种挥发性有机物混合物以满足工业化需求。     

Catalytic ozone oxidation of benzene at low temperature over MnOx/Al-SBA-16 catalyst

The low-temperature catalytic ozone oxidation of benzene was investigated. In this study, Al-SBA-16 (Si/Al = 20) that has a three-dimensional cubic Im3m structure and a high specific surface area was used for catalytic ozone oxidation for the first time. Two different Mn precursors, i.e., Mn acetate and Mn nitrate, were used to synthesize Mn-impregnated Al-SBA-16 catalysts. The characteristics of these two catalysts were investigated by instrumental analyses using the Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction. A higher catalytic activity was exhibited when Mn acetate was used as the Mn precursor, which is attributed to high Mn dispersion and a high degree of reduction of Mn oxides formed by Mn acetate than those formed by Mn nitrate.