High-throughput approach to the catalytic combustion of diesel soot

A methodology for the evaluation of diesel soot oxidation catalysts by high-throughput (HT) screening was developed. The optimal experimental conditions (soot amount, catalyst/soot ratio, type of contact, composition and flow rate of gas reactants) ensuring a reliable and reproducible detection of light-off temperatures in a 16 parallel channels reactor were set up. The temperature profile measured in the catalyst/soot bed under TPO conditions when the exothermic combustion of soot takes place was shown to provide an accurate measurement of the ignition. Its reproducibility and relevance were checked. The results obtained with a reference noble metal free catalyst (La_0.8Cr_0.8Li_0.2O₃ perovskite) agree very well with literature data. Qualitative mechanistic features could be derived from these experiments, stressing the likely limiting step of oxygen transfer from catalyst surface to soot particulates to ignite the soot combustion. Ceria material was shown to be more appropriate than perovskite one. From an HT screening of a large diverse library (over 100 mixed oxides catalysts) under optimized conditions, about 10 new formulations were found to perform better than selected noble metal free reference materials.     

柴油车排气碳微粒催化燃烧研究新进展

主要介绍了国内外柴油车排气碳微粒催化燃烧的研究现状和最新进展,重点分析了贵金属、金属氧化物、金属氧化物碱金属复合型以及过渡金属复合型催化剂在去除柴油车排气中碳微粒中的特点、存在问题以及在实际中的应用,指出未来柴油车排气后处理的发展趋势是同时去除CO、HC、NOx和微粒的四元催化剂。     

Vm/MOx催化剂对柴油碳烟催化燃烧抗硫中毒性能的比较

用柠檬酸络合助溶的等体积浸渍法制备了不同载体(γ-Al2O3 、SiO2 、TiO2、ZrO2和CeO2)负载的系列钒氧化物催化剂,使用红外光谱对催化剂硫中毒老化后的结构进行表征,采用程序升温氧化反应技术评价了硫老化后的催化剂对柴油碳烟催化燃烧的活性.结果表明,负载钒基氧化物催化剂硫老化后,催化剂表面主要以亚硫酸盐物种...     

Thermal stability of Cu-K-V catalyst for diesel soot combustion

This paper reports a study on the thermal stability of a Cu-K-V catalyst, which showed particular promise for low temperature combustion of diesel particulate. Prolonged treatments were performed at high temperatures (400–1000°C) for periods up to 15 days under different gaseous atmospheres. The effect of such treatments on the catalyst composition was investigated by means of weight-decrease measurements and composition analysis (atomic absorption, X-ray diffraction, etc.), whereas the catalyst activity towards soot combustion was determined via thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The apparent activation energy of the soot combustion process was calculated for a collection of catalyst samples, thermally treated according to several different representative conditions, by the Ozawa method on the basis of the DTA results. Some of the thermal treatments (especially those performed at high temperatures: 900–1000°C) resulted in a reduction of the catalyst activity as shown by the increase of both the activation energy and the soot ignition temperature, as a consequence of the volatilisation of at least some of the active compounds of the catalyst itself (KCl, CuCl₂, etc.). Any periodic thermal regeneration of a catalytically-activated trap for diesel emissions (leading to such high temperatures) performed to eliminate any accumulated soot, has thus to be avoided by designing a trap capable of burning out all the soot produced at the diesel exhaust temperatures (< 400°C).     

大孔钙钛矿型氧化物催化剂制备及其对碳烟燃烧的催化性能

采用有机络合和溶液燃烧相结合的方法制备了La_1-xK_xFe_1-yCo_yO₃ (x=0, 0.1;y=0, 0.5)催化剂,通过X射线衍射（XRD）、傅立叶红外吸收光谱（FT-IR）和扫描电镜等分析手段对La_1-xK_xFe_1-yCo_yO₃ 催化剂进行了表征。结果表明,制备的催化剂为钙钛矿型复合氧化物,具有蜂窝状大孔结构,平均孔径大于50 nm。采用超声辅助的方法让碳烟颗粒扩散到催化剂孔道内,利用程序升温反应技术评价了La_1-xK_xFe_1-yCo_yO₃ 催化剂对柴油车尾气中碳烟颗粒物的催化燃烧活性,结果表明,大孔钙钛矿催化剂具有较高的碳烟催化燃烧活性,与纯碳烟的燃烧峰值温度(Tm）相比,下降了（165~239） ℃。通过A位和B位离子的部分取代,可以使钙钛矿型氧化物催化剂的催化氧化性能进一步提高,m降低超过70 ℃。     

Development of catalysts based on pyrovanadates for diesel soot combustion

Pyrovanadates of potassium and cesium were prepared and tested as catalysts for low-temperature combustion of carbon. Their catalytic activity was investigated by both temperature-programmed oxidation and thermogravimetric analysis and compared with that displayed by the metavanadates of the same elements, previously proposed as promising catalysts for soot combustion in diesel emissions. Pyrovanadates show an intrinsic catalytic activity noticeably higher than that of the corresponding metavanadates. In particular, cesium pyrovanadate is capable of lowering the ignition temperature of carbon down to 255°C and to provide a high combustion rate already at about 300°C. Such quite interesting results were confirmed in a pilot plant study on the performance of -Al₂O₃ ceramic foam traps whose pore walls had been lined with catalysts based on either Cs meta- or pyro-vanadates, so as to enable trap self-regeneration by catalytic combustion of the filtered particulate.     

Abatement of diesel-exhaust pollutants: NOx storage and soot combustion on K/La2O3 catalysts

Potassium-loaded lanthana is a promising catalyst to be used for the simultaneous abatement of soot and NO_x, which are the main diesel-exhaust pollutants. With potassium loadings between 4.5 and 10 wt.% and calcination temperatures between 400 and 700 °C, this catalyst mixed with soot gave maximum combustion rates between 350 and 400 °C in TPO experiments, showing a good hydrothermal stability. There was no difference in activity when it was either mixed by grinding in an agate mortar or mixed by shaking in a sample bottle (tight and loose conditions, respectively). Moreover, when the K-loaded La₂O₃ is used as washcoat for a cordierite monolith, there were found no significant differences in the catalytic behaviour of the system, which implies its potentiality for practical purposes.

The influence of poisons as water and SO₂ was investigated. While water does not affect the soot combustion activity, SO₂ slightly shift the TPO peak to higher temperature. Surface basicity, which is a key factor, was analysed by measuring the interactions of the catalytic surface with CO₂ using the high frequency CO₂ pulses technique, which proved to be very sensitive, detecting minor changes by modifications in the dynamics of the CO₂ adsorption–desorption process. Water diminishes the interaction with CO₂, probably as a consequence of an adsorption competition. The SO₂ treated catalyst is equilibrated with the CO₂ atmosphere more rapidly if compared with the untreated one, also showing a lower interaction. The lower the interaction with the CO₂, the lower the activity.

Differential scanning calorimetric (DSC) results indicate that the soot combustion reaction coexists with the thermal decomposition of hydroxide and carbonate species, occurring in the same temperature range (350–460 °C). The presence of potassium increases surface basicity shifting the endothermic decomposition signal to higher temperatures.

We also found that NO₂ strongly interacts with both La₂O₃ and K/La₂O₃ solids, probably through the formation of monodentate nitrate species which are stable under He atmosphere until 490 °C. These nitrate species further react with the solid to form bulk nitrate compounds. The addition of Cobalt decreases the nitrates stability and catalyses the NO_x to N₂ reduction under a reducing atmosphere, which is a necessary step for a working NO_x catalytic trap. Preliminary studies performed in this work demonstrated the feasibility of using these catalysts to simultaneously remove NO_x and soot particles from diesel exhausts. The nitrate formation is still observed during the catalytic combustion of soot in the presence of NO_x, making our K/La₂O₃ a very interesting system for practical applications in simultaneous soot combustion and NO_x storage in diesel exhausts.     

Catalytic combustion of diesel soot on Co, K supported catalysts

Catalysts containing 12% Co and 4.5% K, supported on MgO and CeO₂ have been studied for diesel soot catalytic combustion. It has been found that this reaction occurs by a redox mechanism when Co and K are deposited on any of the above-mentioned supports. On MgO-supported catalysts, CoO_x species are responsible for the supply of oxygen by a redox reaction. In this catalyst, K plays different roles, one of them being the stabilization of the CoO_x particles. On CeO₂-supported catalysts, Co does not significantly improve the activity of the K/CeO₂ catalyst, since in this case the support itself displays redox properties. XPS analyses indicate that the oxygen availability on the surface is much higher on CeO₂ than on MgO. On both CeO₂ and MgO-supported catalysts, K might provide a route for CO₂ release through a carbonate intermediate species. The presence of NO in the gas phase improves the catalytic activity for soot elimination. NO is oxidized to NO₂ on the Co, K/CeO₂ catalyst, and NO₂ is a stronger oxidizing agent than O₂, therefore decreasing the temperature needed to burn the soot.     

Testing molten metal oxide catalysts over structured ceramic substrates for diesel soot oxidation

Onboard tests of an oxide (CoO_x) and a molten mixed oxide catalyst (CoPbO_x) supported on cordierite wall flow filters (Corning Durotrap CO EX80) were performed on rollers with a 1.9-l light duty vehicle for three different driving conditions including two constant speeds with different loadings and a standard European cycle (NEDC). The balance point temperatures obtained in these tests were used to compare the catalytic activity under onboard conditions with laboratory measurements. Onboard tests showed similar catalytic activities with the previous micro-reactor experiments performed in “loose contact” mode [D. Uner, M.K. Demirkol, B. Dernaika, Appl. Catal. B: Environ., in press]. The concentration profiles of the active layer determined by SEM-EDX analysis after use and after aging revealed that the mobile component, PbO_x, migrated in the flow direction and accumulated at the closed end of the channel. There is no direct evidence for the evaporative loss of PbO_x. Regions of high activity indicated by low carbon amounts with unique Pb–Co ratios were determined by SEM analysis.     

La1-xAgxCoO3钙钛矿催化剂的制备及烟碳颗粒催化燃烧性能

采用柠檬酸溶胶-凝胶法制备La_1-xAg_xCoO₃系列钙钛矿催化剂,并对催化剂进行XRD和H₂-TPR表征。XRD结果表明,LaCoO₃钙钛矿中掺杂Ag,部分Ag进入晶格,同时部分Ag以单质形式存在于钙钛矿表面。H₂-TPR结果表明,Ag的掺杂有利于提高LaCoO₃催化剂的低温还原性能。在此基础上,考察催化剂在紧密接触条件下对标准碳和烟碳的催化燃烧性能,发现LaCoO₃钙钛矿可降低标准碳的起燃温度,在LaCoO₃催化剂中掺入Ag,标准碳的燃烧温度进一步降低。催化剂对标准碳的催化燃烧活性随着Ag添加量的增加而逐渐增加。La_1-xAg_xCoO₃催化剂对烟碳的催化燃烧具有较好活性,但Ag含量对催化剂在烟碳催化燃烧中的活性影响较小。为了在烟碳催化燃烧性能和降低卷烟燃烧温度之间建立关联,将催化剂添加到烟丝表面,考察催化剂的添加对卷烟最高燃烧温度的影响,结果表明,当催化剂添加量为烟丝质量的5%时,卷烟的最高燃烧温度可降低28 ℃。     

自蔓延燃烧法制备锰氧化物催化剂及其催化燃烧炭烟颗粒

柴油机尾气中的炭烟颗粒是城市雾霾的主要来源之一,严重污染环境和危害人体的健康。因此,降低和消除柴油车尾气中的炭烟颗粒具有重要的意义。本文以高锰酸钾和一水柠檬酸为原料,通过自蔓延燃烧法成功制备了一系列锰氧化物催化剂。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、N₂吸附-脱附、H₂程序升温还原（H₂-TPR）、O₂程序升温氧化（O₂-TPD）和X射线光电子能谱（XPS）等手段对催化剂进行了表征,并考察了该系列催化剂催化炭烟颗粒燃烧的活性。结果表明,制备的锰氧化物催化剂均具有良好的催化燃烧炭烟活性。当高锰酸钾与一水柠檬酸的摩尔比为12∶1、煅烧温度为450℃时,制备的催化剂具有较低的还原峰温度,较大的比表面积和孔径以及化学吸附氧和Mn⁴⁺含量,从而表现出最佳催化燃烧炭烟颗粒的性能,其催化燃烧炭烟温度T₁₀、T₅₀和T₉₀分别为284℃、327℃和360℃。     

Low temperature diesel soots combustion using copper based catalysts modified by niobium and potassium promoters

Gravimetric temperature programmed oxidation was used to study the combustion of a diesel soot mixed with copper catalysts supported on La₂O₃ or La₂O₂CO₃. In a first step, different systems associating copper oxide with an other metal oxide were prepared and tested in presence of SO₂. The association of copper and niobium was found the most active. The influence of alkali on the activity was also studied. It results that potassium is the most effective in lowering the combustion temperature domain in agreement with literature. Finally, Cu---Nb---K catalysts deposited on lanthanum oxide have an improved catalytic activity at low temperatures compared to Cu---V---K or Cu---Mo---K/TiO₂, reported in literature. For this catalyst, the maximum oxidation rate was observed at ca. 300°C with the combustion starting at about 250°C. A similar behaviour is obtained when replacing Nb by Ta or the support La₂O₃ by either La₂O₂CO₃ or TiO₂.     

Performances of a catalytic foam trap for soot abatement

A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.     

挥发性有机化合物催化燃烧用铂基催化剂的研究进展

负载型Pt催化剂由于具有高活性和良好的稳定性,被广泛应用于挥发性有机化合物(VOCs)的催化完全氧化反应中。系统阐述了载体种类、第二金属组分、催化剂预处理、颗粒尺寸等对催化剂反应活性和稳定性的影响,还概述了Pt催化剂对VOCs完全氧化的催化机理及动力学模型。最后,指出了负载型Pt催化剂今后的发展方向。     

MnOx/Mg-Al2O3催化甲烷燃烧反应的研究

在Al2O3上浸渍Mg（NO3）2溶液,焙烧后制得Mg改性Al2O3（Mg-Al2O3）。以Mg-Al2O3为载体,制备了MnOx/Mg-Al2O3系列催化剂,测试了这些催化剂对甲烷燃烧反应的催化活性。结果表明：Mg的加入有效抑制了Al2O3在高温焙烧时发生γ相变,提高了Al2O3的热稳定性,MnOx/10%Mg-Al2O3对甲烷燃烧的催化活性较高,Mg的适宜加入量为10%。     

Combinatorial synthesis and characterization of mixed metal oxides for soot combustion

A polymerizable-complex method (PCM) was used with automated solution deposition to generate combinatorial libraries of oxide powders that were evaluated for their ability to catalyze the combustion of soot. Chemical compositions were examined for catalytic activity in the soot combustion reaction in parallel using infrared thermography and serially using automated thermogravimetric analysis. Although infrared analysis is much faster, it is not easily suited to analyzing soot combustion in the configuration employed in the present study. Instead, the slower automated thermogravimetric analysis (TGA) was found to be much more reliable and reproducible. The results of characterizing simple oxide systems (Ce–K–O, Cu–K–O, Ce–Na–O and Cu–Na–O) are reported.     

The effect of the contact between platinum and soot particles on the catalytic oxidation of soot deposits on a diesel particle filter

Experiments were performed with two model soot aerosols brought into different forms of contact with Pt aerosol particles, to investigate the effectiveness of this contact in lowering the catalytic soot oxidation temperature. The contact was either generated between individual particles in the aerosol state (Pt-doped soot to simulate a fuel borne catalyst), or by sequential or simultaneous deposition of separately generated soot and Pt aerosols onto a sintered metal filter. (Formation of a soot cake on previously deposited Pt aerosol would simulate a catalyst coated diesel particle filter.) The catalytic activity was determined in all cases from temperature ramped oxidation in air of the filtered particles, and defined as the 50% conversion temperature.

It was found that Pt-doped soot and simultaneously filtered aerosols were both equally effective in reducing the oxidation temperature by up to 140–250 °C for the spark discharge soot (with 3–47 wt% Pt concentration in the soot cake), and by up to 140 °C for the pyrolysis soot (3 wt% Pt). Conversely, the deposition of a thin soot layer of 5–10 μm thickness onto Pt, or vice versa, produced only a slight temperature reduction on the order of about 13–42 °C. These results suggest that the distance between soot and Pt particles plays a key role in promoting an effective oxidation on the filter, which is consistent with the role of Pt particles as local generators of activated oxygen.     

碳烟颗粒在NOx储存催化剂上的燃烧研究进展

柴油车排放的碳烟颗粒和NOx严重危害环境和健康,开发和应用柴油车排放后处理技术势在必行。总结了尾气后处理技术中碳烟颗粒在NOx储存催化剂上燃烧的技术发展路线以及研究进展,包括几种不同贵金属型和稀土混合氧化物型催化剂,同时归纳了其催化作用机理,并对NOx物种对碳烟燃烧活性影响进行归纳分析,对该技术在实际应用中存在的问题和应用前景进行了讨论。     

Study of perovskite‐type oxides and their supported Ag derivatives for catalytic oxidation of diesel soot

A series of perovskite‐type oxides and derived Ag catalysts were prepared, and characterized by N₂‐adsorption, X‐ray diffraction and X‐ray photoelectron spectroscopy. The influences of pretreatment and Ag loading on catalytic activity for diesel soot oxidation were also investigated. Prereduction resulted in a decrease in catalytic activity. An increase in activity with Ag addition was observed, especially with more than 5% Ag loading. This catalyst could be a promising candidate for the catalytic elimination of diesel soot. © 2002 Society of Chemical Industry     

Reduction of soot pollution from automotive diesel engine by ceramic foam catalytic filter

Recent progress in diesel technology demonstrates the possibility of reducing the particulate matter (PM) emissions level combining the high efficiency of common rail engine with exhaust gas after-treatment devices, such as diesel PM filter. Ceramic foam catalytic filter (CFCF), prepared by coating of ceramic foam (CFUF), results in lower temperature and shorter regeneration time due to the higher specific surface, lower pressure drop and good filtration efficiency with respect to CFUF.