外文翻譯（中文）-- 氮氧化物催化技術在汽車尾氣中的應用（節(jié)選）

1、<p><b>　　中文2230字</b></p><p>　　外文資料名稱：氮氧化物催化技術在汽車尾氣中的最新研究 </p><p>　　外文資料出處： Catalysis Surveys from Japan 3(1999)139-146 </p><p>　　附 件： 1.外文資料翻譯譯文 </p&g

2、t;<p>　　附 件： 2.外文原文 </p><p>　　氮氧化物催化技術在汽車尾氣中的應用</p><p>　　日本尼桑汽車有限公司材料研究中心橫須賀237-8523。電子郵件:a-hiroshi@mail。nissan。co。jp;ken-matsushita@mail。nissan。co。jp</p><p>

3、　　目前我們的開發(fā)工作正致力于氮氧化物催化劑在汽油和柴油發(fā)動機中的應用，以進一步提高燃油經(jīng)濟性。那時廢氣溫度會降低，同時廢氣中會有少量烴（碳氫化合物），因此，有必要提高氮氧化物催化劑的活性，使其無論在低溫還是高溫下都能實現(xiàn)氮氧化物-碳氫化物的反應，利用貴金屬催化劑是實現(xiàn)這一目標的有效途徑，在低溫下碳氫吸附和碳氫催化劑技術的提升是提高催化劑效能的關鍵技術。</p><p>　　關鍵詞：氮氧化物催化劑，沸石催化劑，鉑

4、，碳氫吸附，碳氫催化技術的提升</p><p><b>　　1. 導論</b></p><p>　　現(xiàn)在人們強烈要求提高汽車的燃油經(jīng)濟性以減少二氧化碳的排放，為此出現(xiàn)了快速擴散燃燒和直噴式汽油發(fā)動機。在直噴式柴油發(fā)動機已成為主流情況下，可以采用高壓燃油噴射技術進一步提高燃油經(jīng)濟性。</p><p>　　圖1顯示了歐洲和日本現(xiàn)有和建議的汽油和柴油

5、轎車的氮氧化物排放標準。這些標準將逐步加強人們對環(huán)境的重視，正因為如此，迫切需要能大量應用在稀薄燃燒發(fā)動機的高轉(zhuǎn)換效率的催化劑。</p><p>　　由于標準十分嚴格，催化劑的研究有很多的障礙?，F(xiàn)在有些氮氧化物分解技術和氮氧化物催化技術已應用于一些稀薄燃燒發(fā)動機。參照汽油引擎[1,2],汽油發(fā)動機的廢氣中含有很多不飽和碳氫化物，但柴油發(fā)動機沒有有效的控制技術來實現(xiàn)這一目標，它全靠較高的空燃比條件。</p&g

6、t;<p>　　汽油發(fā)動機有很多不飽和碳氫化物，他們有利于降低氮氧化物的排放，另一方面，柴油發(fā)動機排氣含有較多的重碳氫化物，隨著二氧化硫引起的催化劑失效，他們難以用作還原劑。這些條件阻礙了催化劑在實際中的應用。</p><p>　　要求降低排氣溫度以達到低水平碳氫化物剩余，然而這種要求在未來汽油和柴油發(fā)動機的高效率燃燒中是很難實現(xiàn)的。因此，如果開發(fā)出一種高效氮氧化物催化劑，它可以適用于這種情況下，廢

7、氣的清潔將獲得進一步的提升，同時保證了燃油經(jīng)濟性。</p><p>　　本文介紹催化劑技術在實際生產(chǎn)中必須解決的問題和發(fā)展狀況。</p><p>　　圖1.目前和建議的汽油和柴油轎車的氮氧化物排放標準</p><p><b>　　2． 排放特性</b></p><p>　　圖2顯示了歐洲經(jīng)委會（歐州經(jīng)濟委員會）和EUDC

8、(市區(qū)外駕駛循環(huán))熱模式在直噴式柴油發(fā)動機的碳氫化物和氮氧化物的排放排氣溫度的研究結(jié)果。發(fā)動機是四缸2.5升直噴式內(nèi)聯(lián)渦輪增壓。排氣溫度在渦輪增壓器出口測量。大部分氮氧化物時在加速過程中產(chǎn)生的，此時碳氫含量不高，這意味著碳氫化物與氮氧化物之比較低的條件下該催化劑活性很高。</p><p><b>　　圖2</b></p><p>　　表1為柴油機排氣的特點總結(jié)，目前柴

9、油發(fā)動機和汽油之間差異相當明顯。然而，如果將來汽油發(fā)動機的燃燒效率再提高那么他們的排氣特性會越來越像柴油機的。</p><p>　　眾所周知，排氣溫度和環(huán)境碳氫化物和碳氫化物之比時影響氮氧化物催化劑的最重要的因素。圖3顯示了在不完全燃燒汽油發(fā)動機臺架測試氮氧化物和碳氫化物之比對催化劑的影響。這個實驗是測試起燃催化劑的特性。圖中顯示的是催化劑在排氣溫度350至400攝氏度，碳氫化物和氮氧化物之比小于2，此時氮氧化物

10、轉(zhuǎn)化率很低。</p><p>　　圖3 為碳氫化物和氮氧化物之比和氮氧化物轉(zhuǎn)換率間的關系。汽車發(fā)動機（燃）測試：2升，直6缸發(fā)動機，空燃比=19–22 : 1，頻率=約30000次每小時。</p><p>　　要未來的引擎實現(xiàn)較高的燃燒效率就要求排氣溫度較低，這需要在排氣管中碳氫含量較低的情況下制定高效的碳氫氮氧化物催化劑。</p><p>　　3. 催化劑的類型

11、選擇</p><p>　　圖4顯示了催化劑在最大活性溫度下的氮氧化物轉(zhuǎn)化水平，這些數(shù)據(jù)是在過去幾年日本催化學會（CATSJ）和日本化學學會（電子）的年度會議上編訂的。</p><p>　　圖5.氮氧化物轉(zhuǎn)換的三種催化劑。柴油引擎（起燃）測試：2升柴油，平均碳氫和硝之比等于1，頻率為35000次每小時。</p><p>　　實驗的每次實驗條件不一樣因此很難準確的進行。

12、然而，它可能催化劑有三組：貴金屬（鉑類特殊催化劑），金屬離子交換沸石型（銅離子交換分子篩）和堿金屬氧化物型。</p><p>　　圖5顯示了在柴油發(fā)動機臺架上進行的從三個類別和評價氮氧化物催化劑性能。雖然在入口氣體中平均碳氫和硝之比較低，其大小大約為1，鉑催化劑和沸石催化劑的轉(zhuǎn)換率相對較高。</p><p>　　這兩種技術是發(fā)展高效氮氧化物催化劑的關鍵。堿金屬氧化物型要求在超過450攝氏度

13、的高溫下才可以實現(xiàn)高效轉(zhuǎn)化，但實際應用中由于汽車尾氣排放溫度要求越來越低，所以這類催化劑不可能。</p><p>　　表2總結(jié)了這三種類型催化劑的特點。貴金屬催化劑，尤其是其是鉑催化劑在低溫區(qū)域具有較好的氮氧化物轉(zhuǎn)化性能。不過，正如圖6所示，眾所周知鉑催化劑產(chǎn)生的一氧化二氮是一種典型的溫室氣體。所以在使用鉑催化劑時必須采用一些手段抑制來二氧化亞氮形成。</p><p>　　4. 氮氧化物催

14、化劑的發(fā)展戰(zhàn)略</p><p>　　表3顯示了我們催化劑開發(fā)的戰(zhàn)略。通過提高二氧化氮和碳氫化合物的反應以滿足排氣溫度的要求，提高碳氫化物的利用率還有增大催化劑表面的碳氫和硝之比以降低廢氣中碳氫化物含量。</p><p>　　巖本等人提出了一種在中間添加還原劑的方法，在保證二氧化氮含量和碳氫化物的利用條件下提高催化劑的效能。這方法是在較低溫度有效利用貴金屬的改進催化劑的活性。有效利用碳氫吸附

15、和碳氫催化技術的提升是改善催化劑的氮氧化物–碳氫反應的關鍵因素。我們以前報告說，使用沸石碳氫吸附劑可以有效的增加在催化劑表面碳氫和氮氧化物之比[36 , 37]，其他研究人員[ 38 , 39 ]的方法都直接或間接要求適合還原劑反應的廢氣流來增加碳氫和氮氧化物的比例，但這些方法都犧牲了燃油經(jīng)濟性。</p><p><b>　　5．總結(jié)</b></p><p>　　進一

16、步提高燃燒的效率會導致在未來的排氣系統(tǒng)中碳氫含量很少，因此，要加強催化劑在較低溫度下的活性，以更有效地利用碳氧化合物作為氮氧化物</p><p>　　還原劑。利用貴金屬是提高低溫下的催化活性區(qū)有效的方法，但是，使用貴金屬（鉑）催化劑時一定要抑制一氧化二氮形成。</p><p>　　在這項工作中，氮氧化物催化劑可以用一種烴類物質(zhì)來代替，它可以增加碳氫化物對氮氧化物的還原作用。為了氮氧化物催化

17、劑可以在實際中加以應用出了要進一步改進催化劑系統(tǒng)描述的那些還要提高催化劑的活性和耐久性。</p><p>　　Catalysis Surveys from Japan 3 (1999) 139–146</p><p>　　Recent lean NOx catalyst technologies</p><p>　　for automobile exhaust co

18、ntrol</p><p>　　Hiroshi Akama and Kenjiro Matsushita</p><p>　　Materials Research Laboratory, Nissan Research Center, Nissan Motor Co., Ltd., 1, Natsushima-cho, Yokosuka 237-8523, Japan,E-mail:a-h

19、iroshi@mail.nissan.co.jp;ken-matsushita@mail.nissan.co.jp</p><p>　　The current status of our development work on lean NOx catalysts for application to future gasoline and diesel engines is described. As a re

20、sult of further improvements in fuel economy, the temperature of exhaust gas will be lower and there will be smaller quantities of hydrocarbons (HCs) in the exhaust of future engines. Therefore, it is necessary to improv

21、e the activity of lean NOx catalysts at lower temperatures and achieve higher selectivity of the NOx–HC reaction. Utilizing precious metal c</p><p>　　Keywords: lean NOx catalyst, zeolite, platinum catalyst,

22、HC adsorption, HC reforming</p><p>　　Introduction</p><p>　　Improving the fuel economy of automobile engines is strongly demanded today for reducing CO2 emissions. For this reason, there has been

23、 a rapid diffusion of lean-burn and direct-injection gasoline engines. Among diesel engines as well, the direct-injection type has become the mainstream,</p><p>　　and further improvement of fuel economy has

24、been achieved by applying high-pressure fuel injection technology.</p><p>　　Figure 1 shows the current and proposed NOx emission standards for gasoline and diesel passenger cars in Europe and Japan. These em

25、ission standards will be progressively tightened with an eye toward resolving environmental concerns. Due to this regulatory trend, there has been a tendency</p><p>　　to expand the lean-burn operating region

26、 of engines and higher conversion efficiency is being demanded of catalysts.</p><p>　　Tighter standards pose a particularly high hurdle for diesel engines. NOx trap and lean NOx catalyst technologies has bee

27、n applied to some lean-burn and direct-injection Figure 1. Current and proposed NOx emission standards for gasoline and diesel passenger cars. gasoline engines [1,2], but no effective NOx control technology has been impl

28、emented yet for diesel engines that operate under a full lean condition with higher A/F ratios. The exhaust temperature of a diesel engine is lower, and</p><p>　　there are more little HCs remaining in the ex

29、haust compared with a gasoline engine.</p><p>　　There are many C3 to C5 nonsaturated HCs which are advantageous for reducing NOx emissions in gasoline engine exhaust. On the other hand, diesel engine exhaust

30、 contains heavy HCs which are harder to use as a NOx reducing agent, along with SO2 that causes catalytic deactivation. These conditions have thwarted practical application of HC-SCR technology to diesel engines.</p&g

31、t;<p>　　However, the tendency toward lower exhaust gas temperatures and a lower level of residual HCs will result in the same typical exhaust gas conditions for future gasoline and diesel engines that achieve high

32、 fuel combustion efficiency. Therefore, if high-performance lean NOx catalysts are developed which can be applied to such conditions, cleaner exhaust will be obtained, leading to further improvements in fuel economy</

33、p><p>　　This paper describes the current development status of our HC-SCR technologies and discusses the problems that must be addressed to apply these technologies to production vehicles.</p><p>　

34、　Exhaust characteristics</p><p>　　Figure 2 shows profiles of the HC and NOx emissions and exhaust temperature of the direct-injection diesel engine used in this work under the ECE (Economic Commission for Eu

35、rope)+EUDC (Extra-Urban Driving Cycle) hot mode. The engine was a 2.5-liter inline 4-cylinder directinjection turbodiesel. The exhaust temperature was measured at the turbocharger outlet. A high level of NOx was produced

36、 during acceleration, although the HC level was not so high. This means that the ambient HC/NOx ratio is lo</p><p>　　The characteristics of diesel exhaust are summarized in table 1. The differences in exhaus

37、t characteristics between gasoline and diesel engines are quite striking at present. However, if the fuel combustion efficiency of gasoline engines is further improved in the future, their exhaust characteristics will st

38、eadily come to resemble those of diesel engines.</p><p>　　It is well known that the exhaust temperature and ambient HC/NOx ratio are the most important factors affecting the performance of lean NOx catalysts

39、. Figure 3 shows the relationship between the ambient HC/NOx ratio and Nox conversion performance of the Cu-MFI catalyst, a typical lean NOx catalyst, in a lean-burn gasoline engine bench test. This test was conducted to

40、 investigate the light-off characteristics of the catalyst. The plots in the figure are for catalyst inlet exhaust temperatures of </p><p>　　In view of the lower exhaust temperature expected for future engin

41、es that achieve high fuel combustion efficiency it will be necessary to develop high-performance lean NOx catalysts compatible with the low HC level in the exhaust. </p><p>　　3. Selection of catalyst type &l

42、t;/p><p>　　Figure 4 shows a map of the NOx conversion level of lean NOx catalysts as a function of the maximum activity temperature. These data were compiled from reports presented at the annual conferences of

43、the Catalysis Society of Japan (CATSJ) and the Chemical Society of Japan (CSJ) in</p><p>　　the past several years [3–34].</p><p>　　The experimental conditions of each catalyst in the map differ,

44、 making it difficult to compare their activities accurately. However, it is possible to classify the catalysts into three groups: the precious metal type (supported platinum catalyst in particular), the metal ion exchang

45、e zeolite type (copper ion exchange MFI zeolite in particular), and the base metal oxide type.</p><p>　　The NOx reduction performance of a typical catalyst selected from each of the three categories and eval

46、uated in diesel engine bench tests is shown in figure 5. Although the average HC/NOx ratio of the catalyst inlet gas in the activ ity test was at a low level of approximately 1.0, the supported platinum catalyst and the

47、Cu-zeolite catalyst showed comparatively high conversion rates.</p><p>　　The use of these two kinds of catalysts is included among the key technologies for developing high-performance lean NOx catalysts. The

48、 base metal oxide type shows the highest NOx conversion at high temperatures over 450 C, but it is assumed that this type of catalyst will not likely find practical application for automobile exhaust control due to the t

49、rend toward lower exhaust gas temperatures.</p><p>　　The characteristics of these three types of catalysts are summarized in table 2. The precious metal catalyst, es pecially the platinum catalyst, shows bet

50、ter NOx conversion performance in low temperature regions. However, as shown in figure 6, it is well known that the platinum catalyst produces N2O, which is a typical greenhouse gas. Some means of suppressing N2O formati

51、on is necessary when the platinum catalyst is used.</p><p>　　4. Development strategy for lean NOx catalysts</p><p>　　Table 3 shows our strategy for catalyst development. Effective ways of coping

52、 with the trend toward a lower exhaust temperature are to utilize the high reactivity of NO2 and to improve the reactivity of HCs. Improving the rate of HC utilization and increasing the HC/NOx ratio on the catalyst surf

53、ace are effective measures for dealing with the lower HC content in the exhaust gas.</p><p>　　Iwamoto et al. proposed the intermediate addition of reductant (IAR) method [35] as a way of using the high react

54、ivity of NO2 and improving the HC utilization rate. This method is effective in utilizing the precious metal to improve catalyst activity at lower temperatures. Effective use of the HC adsorption/reforming function is a

55、key factor in improving the selectivity of catalysts for the NOx–HC reaction. We have previously reported that the use of zeolite as an HC adsorbent is effective in in</p><p>　　5. Summary</p><p>

56、;　　Further improvement of fuel efficiency will result in a smaller quantity of HCs in the exhaust of future engines. Therefore, catalyst activity at lower temperatures will have to be improved to make more effective use

57、of HCs as Nox reductants. Utilization of precious metals is effective in improving catalytic activity in the lower temperature region, but it is necessary to suppress N2O formation when a precious metal (platinum) cataly

58、st is used. </p><p>　　In this work, lean NOx catalyst performance was improved markedly by using a hydrocarbon-reforming catalyst, which increased the rate of HC utilization as Nox reductants.</p><

59、;p>　　In order to put lean NOx catalysts with high conversion efficiency to practical use, it is necessary to improve the activity and durability of each catalyst, in addition to the further improvement of the catalyst