New technology for production of spherical alumina supports for fluidized bed combustion

Fluidized bed catalytic combustion has proved to be very promising for industrial application. The milestone problem is the development of support and catalyst with a high mechanical and thermal stability. We have developed a new technology for production of alumina supports with desired spherical shape, texture and structure. In this paper several pathways to produce aluminum hydroxide of a pseudoboehmite structure including conventional and new technologies are discussed. Properties of spherical granules depend on the method of granulation and most attention has been paid to development and optimization of hydrocarbon–ammonia molding to produce uniform alumina spheres. Several methods to estimate mechanical strength of spherical aluminas are applied to evaluate mechanical durability of prepared catalysts in a fluidized bed. Optimization of high quality spheres production focused on study of the effect of initial hydroxide properties and molding conditions on properties of the final product. Modification of spherical alumina with oxides of Mg, Ce, La and Si proved to be effective to substantially improve the mechanical and thermal stability. This effect is most pronounced when pairs of these dopes are introduced simultaneously.     

K–V–Ca catalysts supported on porous alumina ceramic substrate for soot combustion: Preparation and characterization

The KCl, KNO₃, CaCl₂, Ca(NO₃)₂, V–Ca and K–V–Ca catalysts supported on alumina ceramic substrates have been prepared. X-ray diffraction and thermogravimetry/differential scanning calorimetry were used to characterize the catalysts, and their catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The catalytic activity of KNO₃ is higher than KCl, and the catalytic activity of Ca(NO₃)₂ is as much as that of CaCl₂. The catalyst containing a higher KNO₃ content exhibits CO₂ adsorption, whereas higher CaCl₂ and Ca(NO₃)₂ content can restrain the adsorption of CO₂. The K–V–Ca catalyst with a molar ratio of 6:1:1 had the lowest soot onset combustion temperature. The melting and oxidation–reduction of KNO₃, oxygen content of catalyst surface, and formation of some eutectic phase may be the key factors in improving catalytic activity of catalysts.     

Catalytic combustion of diesel soot: Deactivation by SO2 of copper and potassium nitrate catalysts supported on alumina

The SO₂ poisoning of Cu KNO₃/Al₂O₃ catalysts used in the catalytic combustion of diesel soot with NO/O₂ feed has been studied in this work. Fresh catalysts show temperatures of maximum combustion rate (T_max) at about 470, 375 and 368 °C for Cu/Al₂O₃, KNO₃/Al₂O₃ and Cu KNO₃/Al₂O₃ respectively. Poisoned catalysts decrease the activity and techniques of vibrational spectroscopy (FTIR) and temperature programmed reduction (TPR) suggest the KNO₃ loss and the formation of potassium sulfate in the mentioned poisoned catalysts.     

Epoxidation of propene on vanadium species supported on silica supports of different structure

Silica supports such as mesoporous materials (SBA-3, SBA-15 and MCM-41), silicalite and amorphous silica were used for accommodation of vanadium species introduced on the support surface by means of impregnation, with vanadium concentration from 1 to 7 wt.%. Catalysts were characterised by means of XRD, low temperature adsorption/desorption of nitrogen, DR UV–vis and Raman spectra and also H₂-TPR measurements. Isolated vanadium species dispersed in the channels of mesoporous SBA-3 with pores diameter related to micropores range, seems to be the most active for propene epoxidation.     

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.     

Application of glass soot catalysts on metal supports to achieve low soot oxidation temperature

K–Ca–Si–O glass was applied to metal supports for use as a catalyst for diesel soot combustion. Glasses were processed from the melt and by a sol–gel route. Catalyst activity for the oxidation of diesel exhaust soot and flame soot from an oil lamp was compared by thermogravimetric analysis (TGA). The results show that a K-based catalytic glass coating on metal substrates can reduce the temperature where half of the engine soot is oxidized (T₅₀) to as low as 360 °C under loose contact conditions, and offers catalytic stability for long term combustion cycling. Scanning electron microscopy observations show that sol–gel glass processing is effective for coating complex wire mesh shapes without pore clogging.     

Iron species incorporated over different silica supports for the heterogeneous photo-Fenton oxidation of phenol

Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313 nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.     

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。     

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).     

多孔氧化铝支撑体的制备与表征

以α-Al2O3粉末为骨料,采用塑性挤压成型技术和固态粒子烧结法制备Al2O3多孔陶瓷支撑体。研究了粘结剂和成孔剂的种类对支撑体性能的影响。研究结果表明:通过选用合适的粘结剂和成孔剂,可制得孔径分布窄、孔隙率高的支撑体。     

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.     

Studies on the redox properties of chromite perovskite catalysts for soot combustion

This paper deals with the preparation (by combustion synthesis), the characterization (by XRD, AAS, BET, SEM, TEM, TPD/R, and XPS analyses), the catalytic activity testing (in a temperature-programmed combustion microreactor and in a DSC analyzer), and the assessment of the reaction mechanism of a series of nanostructured soot combustion catalysts based on La–Cr substoichiometric or alkali-metal-substituted perovskites (La_0.9CrO₃, La_0.8CrO₃, La_0.9Na_0.1CrO₃, La_0.9K_0.1CrO₃, La_0.9Rb_0.1CrO₃, La_0.8Cr_0.9Li_0.1O₃), whose performance is compared with that of the standard LaCrO₃. Some conclusions are drawn concerning the role of each single constituting element on the activity of the most promising catalyst, La_0.8Cr_0.9Li_0.1O₃, which is already active well below 400 °C. The role of weakly chemisorbed O⁻ surface species in particular is pointed out as crucial for the soot combustion process. This indicates the way for the development of new, more active catalysts, possibly capable of delivering amounts of these oxygen species even higher than those obtained (about 700 μmol / g) for the most active Li-substituted lanthanum chromite catalyst developed.     

Catalytic behavior of potassium containing compounds for diesel soot combustion

Alkali doped oxides were synthesized and tested as catalysts for diesel soot combustion using a combinatorial method. It has been found that potassium shows better promotion of the catalytic activity than other alkali elements, and most of the potassium-rich oxides showed similar catalytic behaviors when catalysts and soot were mixed in a slurry. The influence of different mixing methods, including loose contact, tight contact and slurry (wet) mixing with different soot suspensions, on the catalytic behavior of some transition metal oxides, alkali metal carbonates and potassium-containing oxides were studied through thermogravimetry and XRD. The high activity of potassium-containing catalysts is found to be due to the intimate contact between soot and potassium cations caused by polar solvents. Potassium containing catalysts degraded after repeated thermal cycles due to the loss of potassium. It was also found that the addition of transition elements can inhibit the loss of potassium.     

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℃。     

Diesel soot combustion on potassium promoted hydrotalcite-based mixed oxide catalysts

KNO₃ or K₂CO₃ supported Mg–Al hydrotalcite-based mixed oxide catalysts were investigated for the catalytic combustion of diesel soot. The activity of the catalysts before and after reactions with soot was conducted under the flow of air and high purity He gas. It has been found that K shows a great promotion of the catalytic activity, and deactivation was not detected after the reaction with soot in a muffle furnace in a static air atmosphere. The active phases were examined by XRD. The high activity is found to be due to an interaction between K and Mg(Al), which may weaken the Mg(Al)–O bonds, thus facilitating the mobility of the O species.     

Catalytic combustion of soot on metal oxides and their supported metal chlorides

Gravimetric temperature programmed oxidation was used to study the combustion of a soot mixed with various metal oxides and their supported metal chloride catalysts. It is found that the catalytic effect of metal oxide on soot combustion varies depending on property of oxides. CuO and Cr₂O₃ are better catalysts. Addition of some chloride salts (FeCl₃, NaCl and KCl) increases the catalytic activity and KCl exhibits the highest promoting effect by reducing the T_max for about 200 °C. Metal chlorides can also show a synergistic effect on soot combustion. FeCl₃–KCl/CuO can reduce the T_max of carbon oxidation from 780 to 500 °C. Investigation also demonstrates that FeCl₃–KCl/CuO is effective for NO reduction at low temperatures.     

Microstructural investigation and performance evaluation of slip-cast alumina supports

In this work we successfully obtained slip-cast alumina supports with tubular shape. It was investigated the influence of both the starting powder particle size and heat treatment program on the pore structure and water permeability of the prepared materials. This study is supported by a series of experimental tests, including Archimedes method, mercury intrusion porosimetry, scanning electron microscopy, and cold crushing tests. We observed that the heat treatment temperature exhibited a more significant effect on the porosity than the sintering time. It was noticed that, in a general way, the higher the sintering temperature, the smaller the porosity and the larger the apparent density of the prepared materials. In addition, the raise of the sintering temperature from 1100 to 1500 °C increased the cold crushing strength of the tested samples. This behavior was not observed for F2, which seems to be related to the poor sinterability of the starting alumina powder used in its preparation. Among the samples prepared in this work, F2 showed the highest water permeability, followed by F3 and F1. The water permeation behavior of these materials is discussed on the basis of their mean pore size, porosity, genus per unit volume, and pore network tortuosity.     

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.     

The source identification and classification study of soot after combustion

Solid phase microextraction‐gas chromatography‐mass spectroscopy technology was used to extract and analyze three kinds of accelerant soot including diesel soot, gasoline soot, and diesel–gasoline mixture soot. A total of 60 spectrograms have been obtained, analyzed, and compared. It was found that these kinds of soot were quite different with each other in the difference of major target compounds and retention time span, and could be visually identified by the profile of the corresponding spectrogram. A data matrix of 60 * 41 was reached by the characteristic substances corresponding with the retention time in all these 60 spectrograms. With principal component analysis method, two major component variables were obtained to classify the attribution of soot, with perfect classification efficiency of 100%. Hierarchical cluster analysis was further applied for the dendrogram analysis. In spite of the absence of the training set, the classification of 100% accuracy of these kinds of soot could be achieved. Copyright © 2012 John Wiley & Sons, Ltd.