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℃。     

不同水热条件下MnO_2的制备及其催化炭烟颗粒燃烧性能

采用简单的水热法,通过控制不同锰源、酸碱性及水热温度等条件制备一系列MnO_2催化剂,利用SEM、XRD、N_2吸附-脱附和H_2-TPR等对MnO_2催化剂的物化性能进行表征,考察MnO_2催化剂催化炭烟颗粒燃烧的性能。结果表明,制备的纳米棒状MnO_2催化剂均具有良好的催化燃烧炭烟活性,在水热温度120℃、锰源为硝酸锰和酸性条件下,制备的MnO_2催化剂具有最佳催化燃烧炭烟颗粒的性能。     

甲烷氧氯化镧铁复合氧化物催化剂的研究

通过共沉淀法成功合成了一系列焙烧温度不同的镧铁复合氧化物催化剂,通过XRD、N_2-吸附脱附等手段对催化剂进行了表征,探索焙烧温度对催化剂及其甲烷氧氯化反应性能的影响。随着焙烧温度逐渐升高,镧铁复合氧化物颗粒尺寸逐渐变大,比表面积逐渐降低,并且在体相形成了钙钛矿结构。一氯甲烷的选择性随着焙烧温度升高而从51%增加到71%,而一氧化碳的选择性从37%降低到了19%,表明提高催化剂焙烧温度对反应生成主产物抑制副产物有利。     

低温等离子体改性LaCoO_3催化剂去除炭烟颗粒的催化性能

采用低温等离子体对LaCoO_3复合氧化物进行表面改性,利用XRD、FT-IR、H2-TPR和O_2-TPD等对催化剂表面物化性能进行表征,分析等离子体对催化剂表面物化性质的影响。采用程序升温氧化反应评价催化剂对模拟柴油机炭烟催化氧化的活性。结果表明,等离子体改性促进了催化剂表面晶格氧的活化,增加了活性氧物种数目,从而增强了催化剂对炭烟催化氧化活性,炭烟催化起燃温度Ti由278℃降到274℃,峰值温度Tm由354℃降至345℃,燃尽温度Tf由425℃降至386℃。     

CO加氢选择性合成C_2-含氧化物的Rh/V/SiO_2催化剂的反应特性

本研究从RhCl_3·3H_2O和VOCl_2·5H_2O及SiO_2出发制备了对C_2-含氧化物的生成具有良好活性和选择性的Rh/V/SiO_2催化剂。当V/Rh=0.5～1(原子比),还原温度在250～300℃时催化剂的活性和选择性都较佳。适当地提高反应的压力、温度和空速,可在选择性基本不变的条件下,使C_2含氧化物的生成速率大大提高。在6大气压、230℃和24000毫升/时·克催化剂下可获得C_2-含氧化物生成选择性达80％,生成速率达0.9克/时·克催化剂C_2-含氧化物的良好结果。     

B–Si–Zr掺杂炭材料的制备及其抗氧化性能

以煤沥青甲苯可溶组分、聚碳硅烷、吡啶硼烷和ZrB_2有机前驱体为原料,通过低温裂解制备掺杂沥青,经过不同温度热处理得到B–Si–Zr掺杂炭材料,考察了掺杂炭材料抗氧化性能。用X射线衍射仪、扫描电子显微镜等对B–Si–Zr掺杂炭材料氧化前后的物相组成和微观结构进行表征。结果表明:1600℃热处理得到的B–Si–Zr掺杂炭材料中,ZrB_2陶瓷颗粒逐渐形成,在氧化过程中,SiC和ZrB_2等陶瓷与氧气反应生成SiO_2、B_2O_3和ZO_2,氧化物在炭材料表面形成保护膜,该热处理温度得到的掺杂炭材料抗氧化性较强。     

埋炭气氛下碳热、铝热、硅热还原TiO2反应的热力学分析

通过热力学计算,探讨了埋炭气氛下碳热、铝热和硅热还原TiO2生成Ti(C,N)的可能性、生成途径、生成产物的相对稳定性以及对3种还原反应进行了对比.结果表明:埋炭气氛下,3种还原反应均可发生且生成的钛的非氧化物是以Ti(C,N)形式存在;在铝热和硅热反应中,不稳定的中间产物AlN和Al4C3会转为稳定的刚玉相,而Si3N4则转化为稳定的碳化硅或方石英;通过比较发现,碳热还原TiO2法是制备钛的非氧化物陶瓷最经济有效的方法.     

蒎烯异构化制莰烯催化剂的研究

研究了固体酸催化剂(编号为SA-ISO)在蒎烯异构化制莰烯反应中的性能,考察了反应温度、蒎烯质量空速及颗粒大小对催化剂反应性能的影响,在优化的条件下考察了催化剂的稳定性。结果表明,催化剂直径小于2mm的条件下,可以消除内扩散对异构化反应的影响。在反应温度130℃、蒎烯空速为0.5h-1条件下,蒎烯转化率98.9%,莰烯选择性78.7%,成型催化剂在固定床单管反应器上连续稳定反应8 000h以上。利用N2吸附-脱附、NH3程序升温脱附(NH3-TPD)和热重-差热(TG-DTA)等测试技术对SA-ISO催化剂进行了表征和分析,结果表明,SA-ISO催化剂反应过程中逐渐积碳导致比表面积和孔容下降,但催化剂未出现失活迹象,催化剂有较高容炭能力,具有良好的工业应用的前景。     

逆水煤气变换耦合乙烷脱氢高选择性制备乙烯反应的研究进展

综述了近年来国内外有关利用逆水煤气变换耦合乙烷脱氢制备乙烯反应的研究状况,讨论了该反应的历程和机理。文献表明,担载型铬氧化物、含铬分子筛、纳米氧化物粒子等具有较好的催化活性,CO2的主要作用是通过逆水煤气变换来消除乙烷脱氢产物H2,并与表面积炭反应提高乙烷转化率及催化剂稳定性。反应的关键是选择适宜的催化剂。     

CH4-CO2重整反应过程中炭催化剂失重特性

在反应温度950～1 200℃,升温速度20℃/min的实验条件下,用热重分析仪对炭催化剂作用下CO2气化和CH4-CO2重整过程中炭催化剂失重进行了研究.结果表明,在炭催化剂-CO2气化过程中,随着CO2流量的增加和反应温度的提高,炭催化剂的失重率明显增加,CO2流量和反应温度是造成炭催化剂失重的重要原因.在炭催化CH4-CO2重整过程中,随着CO2/CH4比值的增加炭催化剂质量先增加后减少,表明炭催化剂的失重率可以通过CO2/CH4来调节;而随反应温度升高,炭催化剂质量变化表现为低温(<1 100℃)单阶段和高温(>1100℃)双阶段两种类型.即在反应温度低于1 100℃时,炭催化剂失重反应主要由化学反应过程控制,CH4裂解碳沉积和CO2的气化消碳很快达到平衡,炭催化剂失重宏观上表现为维持恒定的单一阶段;当反应温度高于1 100℃后,炭催化剂的失重表现为双阶段,开始的第一阶段,主要受化学反应过程控制.炭催化剂急剧失重,然后逐步过渡到扩散过程控制的第二阶段,失重率逐渐趋于平缓;炭催化CH4-CO2重整过程中,反应温度和CO2/CH4比是导致炭催化剂失重的主要因素.     

Fullerene-Like Soot from EuroIV Diesel Engine: Consequences for Catalytic Automotive Pollution Control

Soot particulates from an EuroIV diesel engine are sampled and investigated by high-resolution electron microscopy (HRTEM) and thermal gravimetry. The experiments reveal a drastic reduction of primary particle size down to less than 20 nm, much smaller than that emitted by earlier diesel engines. HRTEM reveals primary particles with deformed fullerenoid structures. The defective fullerenoid soot is more prone to oxidation than the soot of a black smoking diesel engine. Our findings may initiate a critical review of the current strategy for the reduction of soot emission from diesel engines. The newly developed engines reduce the quantity of soot emitted, they also emit smaller soot particles with a fullerene-like structure into the exhaust.     

Diesel particulate emission control

This paper reviews the emission control of particulates from diesel exhaust gases. The efficiency and exhaust emissions of diesel engines will be compared with those of otto engines (petrol engines). The formation of particulates (or “soot”), one of the main nuisances of diesel exhaust gases, will be briefly outlined. The effects of various emission components on human health and the environment will be described, and subsequently the emission standards for particulates and for NO_x, which have been introduced worldwide, will be summarized. Possible measures for reducing exhaust emissions of particulates and NO_x will be discussed, such as the use of alternative fuels, modifications to the engine and the use of aftertreatment devices. It will be made clear that aftertreatment devices may become necessary as diesel emission standards become more stringent, in spite of important progress in the other fields of reducing exhaust emissions. Selective catalytic reduction via hydrocarbons, ammonia or urea, a possible aftertreatment method for NO_x emission control, will be discussed briefly. Filters for collecting particulates from diesel exhaust gases will be examined in more detail and aftertreatment control systems for particulate removal will be reviewed. These can be divided into (i) non-catalytic filter based systems which use burners and electric heaters to burn the soot once it has been collected on the filter; (ii) catalytic filter-based systems which consist of filters with a catalyst coating, or filters used in combination with catalytically active precursor compounds added to the diesel fuel; and (iii) catalytic non-filter-based systems in which gaseous hydrocarbons, carbon monoxide and part of the hydrocarbon fraction of the particulates are oxidized in the exhaust gases. Finally, recent trends in diesel particulate emission control will be discussed, indicating the growing importance of the catalytic solutions: the fast introduction of non-filter-based catalysts for diesel engines and the possible application of filters in combination with catalytically active precursor compounds added to diesel fuel.     

Sn催化剂对柴油车排气颗粒去除效果

制备了以Sn为活性组分,以Cu、K、V为助催化剂,以TiO₂/γ-Al₂O₃/堇青石为载体的催化剂,催化剂在700℃下于空气中在马弗炉活化3h.采用DSC/TG测试方法确定催化剂的活性.研究发现,以Sn为活性组分的催化剂能显著降低颗粒的起燃温度和扩大燃烧温度范围,Cu、 K、V的添加能进一步降低起燃温度,而燃烧温度范围却稍有所变窄.活化会降低催化活性,活化导致活性下降的原因不是由催化剂的烧结引起的,而是由活性组分的挥发流失造成的.     

Simultaneous removal of NO and carbon particulates over lanthanoid perovskite-type catalysts

The simultaneous removal of carbon particulate and NO_x has been studied over perovskite-type oxides prepared by malic acid method. The catalysts were modified to enhance the activity by substitution of metal into A- or B-site of perovskite oxide. In the LaCoO₃ catalyst, the partial substitution of Cs into A-site enhanced the catalytic activity in the combustion of soot particulate and NO reduction. In La_1−xCs_xCoO₃ catalysts, the ignition temperature of carbon particulate decreases with increasing x values and shows almost constant values at substitution of x>0.2 and NO conversion also shows the similar tendency. In the Cs-substituted oxide, the ignition temperature of carbon particulate slightly decreased in the order Co>Mn>Fe of B-site metal cation but NO conversion showed almost similar values. With increasing NO concentration, NO conversion decreased but the ignition temperature moved to high temperature when the NO concentration was higher than 1000 ppm. The carbon particulate played an important role on the reduction of NO, but NO had little effect on the oxidation of carbon particulate.     

Rôles of catalytic oxidation in control of vehicle exhaust emissions

Catalytic oxidation was initially associated with the early development of catalysis and it subsequently became a part of many industrial processes, so it is not surprising it was used to remove hydrocarbons and CO when it became necessary to control these emissions from cars. Later NOx was reduced in a process involving reduction over a Pt/Rh catalyst followed by air injection in front of a Pt-based oxidation catalyst. If over-reduction of NO to NH₃ took place, or if H₂S was produced, it was important these undesirable species were converted to NOx and SOx in the catalytic oxidation stage. When exhaust gas composition could be kept stoichiometric hydrocarbons, CO and NOx were simultaneously converted over a single Pt/Rh three-way catalyst (TWC). With modern TWCs car tailpipe emissions can be exceptionally low. NO is not catalytically dissociated to O₂ and N₂ in the presence of O₂, it can only be reduced to N₂. Its control from lean-burn gasoline engines involves catalytic oxidation to NO₂ and thence nitrate that is stored and periodically reduced to N₂ by exhaust gas enrichment. This method is being modified for diesel engines. These engines produce soot, and filtration is being introduced to remove it. The exhaust temperature of heavy-duty diesels is sufficient (250–400 °C) for NO to be catalytically oxidised to NO₂ over an upstream platinum catalyst that smoothly oxidises soot in the filter. The exhaust gas temperature of passenger car diesels is too low for this to take place all of the time, so trapped soot is periodically burnt in O₂ above 550 °C. Catalytic oxidation of higher than normal amounts of hydrocarbon and CO over an upstream catalyst is used to give sufficient temperature for soot combustion with O₂ to take place.     

柴油车尾气四效组合催化剂的研究

提出设计双层组合催化剂净化新技术,即碳黑氧化燃烧催化剂床层和NOx还原催化剂床层的组合,该组合催化剂对柴油机尾气四种污染物的消除具有较高的催化活性。采用浸渍法制备了Al₂O₃负载不同量的La_0.8K_0.2MnO₃和相同负载量、不同K含量的La_1-xK_xMnO₃/Al₂O₃催化剂作为氧化催化剂处理碳烟、CO和HC;采用等体积浸渍法制备Cr/HZSM-5、Mo/HZSM-5、W/HZSM-5三系列催化剂作为还原催化剂处理NOx,并将其进行组合,得到优良的氧化还原组合催化剂,同时处理柴油车尾气中的四种污染物。在模拟柴油车尾气组成条件下,用乙炔代表烃类物质并采用固定床微型反应装置,考察了所制备的双层四效组合催化剂净化柴油车尾气的催化性能。研究发现,负载质量分数为50%的La_0.5K_0.5MnO₃/Al₂O₃和负载量为1.42×10^-4mol·g^-1的W/HZSM-5组合催化剂对于同时消除柴油车尾气NO、碳颗粒、CO和HC有较好的效果。NO还原为N₂的转化率在反应温度范围最高可达79%,同时碳颗粒的燃烧峰值温度为448 ℃,碳颗粒燃烧生成CO₂ 的最大选择性可达98%,乙炔完全转化的温度为364 ℃,从而实现了四种有害物质的同时催化净化。     

Gasification of carbonaceous particulates

The reactions of soot particulates and carbons with three oxidising agents expected in the exhaust gases from a diesel engine have been studied. Nitrogen dioxide has been found to be an efficient gasifying agent for carbons, carbon oxides and nitric oxide being produced. The reaction with diesel particulates commences above c. 150°C: with graphite, gasification became significant only above c. 550°C. The presence of oil on the particulates does not affect gasification. © 1998 SCI.     

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.     

Emission characteristics of high speed, dual fuel, compression ignition engine operating in a wide range of natural gas/diesel fuel proportions

In the effort to reduce pollutant emissions from diesel engines various solutions have been proposed, one of which is the use of natural gas as supplement to liquid diesel fuel, with these engines referred to as fumigated, dual fuel, compression ignition engines. One of the main purposes of using natural gas in dual fuel (liquid and gaseous one) combustion systems is to reduce particulate emissions and nitrogen oxides. Natural gas is a clean burning fuel; it possesses a relatively high auto-ignition temperature, which is a serious advantage over other gaseous fuels since then the compression ratio of most conventional direct injection (DI) diesel engines can be maintained high. In the present work, an experimental investigation has been conducted to examine the effects of the total air-fuel ratio on the efficiency and pollutant emissions of a high speed, compression ignition engine located at the authors’ laboratory, where liquid diesel fuel is partially substituted by natural gas in various proportions, with the natural gas fumigated into the intake air. The experimental results disclose the effect of these parameters on brake thermal efficiency, exhaust gas temperature, nitric oxide, carbon monoxide, unburned hydrocarbons and soot emissions, with the beneficial effect of the presence of natural gas being revealed. Given that the experimental measurements cover a wide range of liquid diesel supplementary ratios without any appearance of knocking phenomena, the belief is strengthened that the findings of the present work can be very valuable if opted to apply this technology on existing DI diesel engines.     

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.