CN106794422A - 具有减少的活化时间的催化转化的装置 - Google Patents

具有减少的活化时间的催化转化的装置 Download PDF

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CN106794422A
CN106794422A CN201580054977.4A CN201580054977A CN106794422A CN 106794422 A CN106794422 A CN 106794422A CN 201580054977 A CN201580054977 A CN 201580054977A CN 106794422 A CN106794422 A CN 106794422A
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塞巴斯蒂安·多内
奥里莱恩·范登伊恩德
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Abstract

一种用于将NOx催化转化为N2和/或将CO催化转化为CO2的装置,所述装置包括:陶瓷载体(4),所述陶瓷载体具有至少多个通道;热屏蔽件(6),所述热屏蔽件由绝热材料制成,且覆盖所述通道的内表面的至少一部分;多孔SiC(8),所述多孔SiC至少部分地覆盖所述热屏蔽件(6),从而所述SiC(8)通过所述热屏蔽件(6)与所述载体隔开;至少在所述SiC上的一种或多种转化催化剂(12)。

Description

具有减少的活化时间的催化转化的装置
技术领域
本发明涉及一种具有减少的活化时间的催化转化的装置,该装置用于气体的去污染,尤其是用于机动车辆的废气的去污染。
背景技术
内燃机(尤其是柴油发动机)产生含氮氧化物(通常被称为NOx)的废气,该含氮氧化物的废气主要由一氧化氮NO和一氧化碳CO组成。
我们正在寻求降低这种污染性排放物。
去污染系统被设置在排气管线上,以处理废气,尤其是将NOx还原为N2,并且将CO氧化为CO2
去污染系统的一个实例包括NOx捕集阱。该捕集阱在柴油的条件下包括还原催化剂,其需要经由发动机(通过燃料的后喷射)来定期供应还原剂,并且产生60%至70%NO的还原,然而,引起2g/km的CO2的额外消耗。
该捕集阱以贫化(pauvre)和富集的操作模式连续交替地运行,第一阶段对应于在发动机出口处使NOx储存在气态排出物中,第二阶段对应于它们的还原。
NOx捕集阱包括通常由氧化铝、二氧化铈或氧化锆的混合物形成的载体,在该载体上,依次沉积有碱金属或碱土金属(例如Ba或Sr)氧化物,随后沉积有贵金属(例如铂或铑)。铑主要用于氮氧化物的还原反应,而铂和钯对于CO和烃类的氧化具有活性。
然而,尽管在柴油发动机排出的高度氧化性气体流中并不难进行污染物的催化氧化,但是在这种环境中并不能将NOx完全还原成N2
其他捕集阱存在并且包括由SiC制成的载体,该SiC覆盖形成催化剂的贵金属。SiC的优点是具有良好导热性,这就使得催化剂能够快速升高温度,所述催化剂在约150℃至600℃之间的温度下具有活性,温度的升高归因于废气的热量。然而,这种良好的导热性所具有的缺点是,导致催化剂载体的温度快速下降。此外,SiC是一种易碎且昂贵的材料。
如文献US 6 986 247中描述了现有的催化转化器,该催化转化器包括:热电发电机,用于由废气的热量来产生电力,并且利用该电力来在车辆变凉时加热催化剂,以减少催化剂的活化时间。这些转换器的制造复杂且利用热电发电机以及用于存储由热电发电机产生的电力的构件。
发明内容
因此,本发明的一个目的是提供一种用于催化转化的装置,所述催化转化的装置与现有技术的装置相比,具有改进的转化效率和简化的制造。
上述目的通过这样的装置来实现:所述装置包括例如由陶瓷制成的载体,在载体上的绝热材料层,在绝热材料层上的多孔SiC的层,以及在所述多孔SiC的层上的一种或多种催化剂。
该方式能够获得SiC的良好导热性的优点,由于其并未形成载体而无需控制其脆性。由于SiC的良好导热性,启动时温度迅速上升。此外,由于载体和SiC之间的绝热性,热量被储存在SiC中,这有助于在整个操作过程中保持温度或至少减慢了温度的下降;因此,可使催化剂保持在活化状态或接近活化的温度下,从而加速它们的再活化。
有利地,通过化学气相沉积来沉积一种或多种催化剂,这所带来的优点是使得该一种或多种催化剂的活化温度降低,例如降低15℃。
换句话说,生产催化转化器,其中载体由耐性且低成本的材料制成,并且仅产生一层SiC,这确保一种或多种催化剂的“热化”,保证了该一种或多种催化剂更快和更持续的活化,从而能够在发动机启动时非常快速地处理废气,并且提供对气体的连续或基本连续的处理。因此,与现有技术的装置排出的量相比,有效排放到空气中的废气中所含的污染物的量大大减少。
因此,本发明的主题是一种用于催化转化的装置,所述装置包括:
陶瓷载体,所述陶瓷载体设置有至少一个表面;
热屏蔽件,所述热屏蔽件由至少一种绝热材料制成,且覆盖所述载体的表面的至少一部分;
多孔SiC,所述多孔SiC至少部分地覆盖所述热屏蔽件,从而所述SiC通过所述热屏蔽件与所述载体隔开;
至少在所述多孔SiC上的一种或多种转化催化剂。
热屏蔽件可包括至少一个层,所述层由选自TiN、YSZ、AlZ和TiAlN的至少一种材料制成。
有利地,在所述SiC和所述一种或多种转化催化剂之间插入有缓冲层。
所述缓冲层的一种或多种材料可选自CeO2、ZrO2、Al2O3、BaCO3
所述一种或多种催化剂可选自Pt、Pd、Rh、Ag和上述金属的组合。
在一个有利的实施例中,载体由堇青石或莫来石制成。
所述载体可包括通道,所述载体的表面由所述通道的内表面构成。
有利地,所述多孔SiC具有在55%和70%之间、优选在60%和65%之间的孔隙率。
本发明的另一主题是一种用于处理内燃机的废气的装置,所述装置包括至少一个根据本发明所述的用于催化转化的装置。
本发明的另一主题是一种用于根据本发明所述的用于催化转化的装置的制造方法,所述制造方法包括以下步骤:
a)生产陶瓷载体;
b)在所述载体的表面的至少一部分上形成热屏蔽件;
c)在所述热屏蔽件的至少一部分上形成多孔SiC;
d)在所述SiC上形成一种或多种转化催化剂。
步骤d)有利地通过化学气相沉积来进行。
在步骤d中,可沉积氧化催化剂和还原催化剂。例如,沉积所述氧化催化剂和所述还原催化剂在不同的子步骤中进行。
在步骤b)中,可形成SiC的连续层;随后,例如,通过加热至800℃和1100℃之间使所述连续层进行多孔化(porosification)步骤。
附图说明
参照附图阅读以下说明书之后,将更好地理解本发明,其中:
图1为根据本发明的催化转化载体的一个实例的透视图;
图2为图1中用于催化转化的装置的区域的横截面图的示意图。
具体实施方式
图1示出了根据本发明的用于催化转化的装置的一个实例。该装置用于布置在排气管道中,并且使所有的废气流均流经该装置。该装置包括沿废气流方向延伸的多个通道2。废气与含有催化剂的通道内表面相接触,使得例如NOx转化成N2以及CO转化成CO2。在所示的实例中,通道具有正方形横截面,然而它们可以具有六边形横截面以类似蜂窝结构。更通常地,通道具有多边形横截面。此外,使气体和装置之间具有良好接触水平的任何其它形状都是合适的。
作为变型,该装置可以包括其中一个端部被封闭的通道。例如,包括封闭的纵向端部的通道被包括封闭的相对纵向端部的通道所包围,以迫使气体通过通道的壁,由此通道的壁是多孔的。这种结构使得气体在装置中存在的时间增加,从而增加被转化的污染物的量。
图2示出了示意性示出的通道2的壁的横截面图。
该装置包括由诸如莫来石、堇青石的陶瓷材料或各向同性陶瓷制成的载体4;载体形成装置的框架并且包括彼此平行的多个通道。载体例如由孔隙率在30%至70%之间的多孔材料制成。
对载体的陶瓷进行选择以使得其脆性小于SiC的脆性,并且有利地具有低于SiC的成本价格。此外,载体4的材料是电绝缘且绝热的。
莫来石和堇青石具有低于1W/m.K的低导热系数。
该装置包括在载体4上的热屏蔽件6,该热屏蔽件6包括一种或多种绝热材料6,所述绝热材料至少部分地覆盖载体4。热屏蔽件6可包括一层或多层绝热材料
该装置进一步包括:在材料6上的多孔SixCy 8,其中0<x<1且0<y<1;在SixCy上的缓冲层10(也被称为“涂层(wash-coat)”);以及在缓冲层10上的用于与废气接触的一种或多种催化剂12。
为了简单起见,以下将SixCy称为SiC。
SiC的孔隙率提供了大的延伸的表面,从而能够在保持相同的SIC的表面积的同时减小载体的大小;或者在保持相同的载体大小的同时增加SiC的表面积。此外,多孔SiC具有引起废气流发生涡流的结构,这改善了气体和催化剂之间的接触并且使转化反应更容易发生。多孔SiC的结构可以足够细以形成纳米结构。SiC具有有效的孔隙率。例如,通过BET法(Brunauer-Emmett-Teller理论)确定该有效的孔隙率在55%至70%之间、优选在60%至65%之间。
形成热屏蔽件6(例如由一层或多层构成)的一种或多种材料选自例如TiN、YSZ、AlZ(Al2O3和ZrO2的混合物,其中具有5%和30%ZrO2)或TiAlN。形成热屏蔽件的一种或多种材料具有优选小于10W/m.K的导热率。YSZ具有阻止材料内裂缝的优点。
在所示的实例中,热屏蔽件6是不连续的。这种不连续性可能是载体的异质性的结果。热屏蔽件以连续的方式覆盖载体的装置并不在本发明的范围之外。
缓冲层10例如由CeO2、ZrO2、Al2O3或BaCO3制成。
一种或多种催化剂12例如选自Pt、Pd、Rh、Ag或它们的组合。
优选地,一种或多种催化剂选择性地沉积在SiC上。
应该注意的是,Pt和Pd优选用于将CO氧化成CO2,Rh优选用于将NOx还原成N2
为了说明的目的,载体的厚度在1mm和2mm之间;热屏蔽层的厚度在20μm和250μm之间,优选地为约150μm+/-20μm;多孔SiC层的厚度在1μm和50μm之间,优选在5μm和10μm之间,并且可为不连续的催化剂层的厚度在4nm和12nm之间。
以下段落将描述催化转化的装置的运行模式。该模式参照将NOx转化为N2来描述。
例如,该装置布置在排气管道中。在内燃机启动时,该装置,并且尤其催化剂是冷的,因此未被活化且不能将NOx转化成N2
热废气与冷的装置的表面进行接触;然而,由于SiC的良好的导热性,其温度快速升高,更重要的是,热屏蔽件6在载体的一侧限制了热损失。因此,SiC朝向催化剂传递热量,因此催化剂迅速升温并迅速地被活化。它们已经能够将废气中所含的NOx转化为N2。活化温度在约150℃至600℃之间。
此外,由于多孔SiC与载体绝热,所以SiC形成热储存器。因此,它形成用于催化剂的可用热源,使催化剂保持在接近活化温度的温度下,或者甚至保持在活化温度下。因此,在关闭/启动阶段期间,缩短了催化剂活化过渡(transitoires)时间,从而对废气进行基本连续的去污染。
这就使得排放到空气中的NOx的减少甚至消除。
现将描述用于制造根据本发明的装置的一种方法。
在第一步骤中,生产例如由堇青石或莫来石制成的陶瓷载体。载体具有例如图1所示的大体形状。
在随后的步骤中,在载体上形成热屏蔽件6。
在随后的步骤中,在热屏蔽件上形成多孔SiC。有利地,最初沉积连续的SiC层;随后使该层进行多孔化。SiC层例如使用聚硅氧烷例如通过涂覆来制成。然后例如在800℃至1100℃之间加热该层,从而使得该层为多孔的。
在随后的步骤中,例如通过浸渍形成涂层。
在随后的步骤中,将一种或多种催化剂沉积在涂层上。
优选地,通过化学气相沉积或CVD并且优选以选择性方法在SiC上沉积催化剂。
通过CVD在多孔SiC上进行沉积具有的优点是:由于该沉积在SiC上选择性地进行,所以减少了所需催化剂的量。实际上,与在堇青石上进行的催化剂的沉积相比,在SiC上的催化剂的沉积在更低的温度下进行;因此通过将SiC加热到足够的温度以确保仅在SiC上沉积催化剂,所得到的沉积中,催化剂仅沉积在SiC上。由于催化剂通常涉及贵金属,所以催化剂所需量的这种减少甚至是更有利的。所需量的催化剂可以降低高达50%。CVD例如在300℃至400℃的温度下进行。为了进行CVD,对将要进行沉积的物体例如通过辐射进行加热,然后将其放置为与含有待沉积的所述金属的前体的气体混合物或待沉积的所述金属和/或它们合金的前体的气体混合物相接触。
如上所述,Pt和Pd优选用于将CO氧化成CO2,Rh优选用于将NOx还原成N2
优选地,用于催化转化的装置既包括氧化催化剂又包括还原催化剂。
优选地,催化剂的沉积在两个子步骤中进行:
例如,在第一子步骤期间,沉积一种或多种氧化催化剂,例如Pt和/或Pd;并且在第二子步骤期间,沉积一种或多种还原催化剂,例如Rh。该顺序不是限制性的,可在氧化催化剂之前沉积还原催化剂。
由于本发明,催化剂被更快地活化。例如,考虑到在现有技术的装置中,催化剂进行冷启动试验的NEDC(新欧洲行驶循环),催化剂从冷起动到被活化需要约1分钟,而在装置中根据本发明,该活化时间每循环减少5秒至20秒。此外,催化剂可以连续地或基本连续地被活化,从而改善对气体的去污染。此外,由转化装置的表面的纳米结构产生的涡流进一步促进污染物的转化。
例如,相对于需要在还原催化剂中注入燃料的柴油发动机中的去污染方法,根据本发明的装置避免了对所述注入的需要,从而节省了排出的二氧化碳的量。
此外,根据本发明的装置的结构通过CVD能够降低贵金属的量,并且还使得催化剂活化温度降低约15℃,这提供了甚至更快的催化剂活化。
在多孔SiC上通过CVD沉积的催化剂具有使其更具活性小面(facettée)结构以及受控尺寸(例如在4nm和12nm之间)的结构。这在所使用的材料和活性材料之间产生最佳产率。
仅用于催化转化CO或NOx的装置并不在本发明的范围之外。
此外,本发明适用于任何物质的催化转化,由此选择一种或多种催化剂以适用于一种或多种待转化的物质。
此外,本发明不限于用于机动车辆的废气转化装置,还涉及用于产生需要处理的气体的任何系统。

Claims (13)

1.一种用于催化转化的装置,所述装置包括:
陶瓷载体(4),所述陶瓷载体(4)设置有至少一个表面;
热屏蔽件(6),所述热屏蔽件(6)由至少一种绝热材料制成,且覆盖所述载体(4)的表面的至少一部分;
多孔SiC(8),所述多孔SiC(8)至少部分地覆盖所述热屏蔽件(6),从而所述SiC(8)通过所述热屏蔽件(6)与所述载体隔开;
至少在所述多孔SiC上的一种或多种转化催化剂(12)。
2.根据权利要求1所述的用于催化转化的装置,其中,所述热屏蔽件包括至少一个层,所述层由选自TiN、YSZ、AlZ和TiAlN的至少一种材料制成。
3.根据权利要求1或2所述的用于催化转化的装置,其中,在所述SiC(8)和所述一种或多种转化催化剂(12)之间插入有缓冲层(10)。
4.根据权利要求3所述的用于催化转化的装置,其中,所述缓冲层(10)的一种或多种材料选自CeO2、ZrO2、Al2O3、BaCO3
5.根据权利要求1至4中任一项所述的用于催化转化的装置,其中,所述一种或多种催化剂(12)选自Pt、Pd、Rh、Ag或上述金属的组合。
6.根据权利要求1至5中任一项所述的用于催化转化的装置,其中,所述载体(4)由堇青石或莫来石制成。
7.根据权利要求1至6中任一项所述的用于催化转化的装置,其中,所述载体(4)包括通道(2),所述载体(4)的表面由所述通道(2)的内表面构成。
8.根据权利要求1至7中任一项所述的用于催化转化的装置,其中,所述多孔SiC(8)具有在55%和70%之间、优选在60%和65%之间的孔隙率。
9.一种用于处理内燃机的废气的装置,所述装置包括至少一个根据权利要求1至8中任一项所述的用于催化转化的装置。
10.一种用于权利要求1至8中任一项所述的用于催化转化的装置的制造方法,所述制造方法包括以下步骤:
a)生产陶瓷载体;
b)在所述载体的表面的至少一部分上形成热屏蔽件;
c)在所述热屏蔽件的至少一部分上形成多孔SiC;
d)在所述SiC上形成一种或多种转化催化剂。
11.根据权利要求10所述的制造方法,其中,步骤d)通过化学气相沉积来进行。
12.根据权利要求10或11所述的制造方法,其中,在步骤d)中,沉积氧化催化剂和还原催化剂,并且其中,在不同的子步骤中,沉积所述氧化催化剂和所述还原催化剂。
13.根据权利要求10至12中任一项所述的制造方法,其中,在步骤b)中,形成SiC的连续层;随后,例如,通过加热至800℃和1100℃之间,使所述连续层进行多孔化步骤。
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