CN106414983B - 具有在egr回路中的n2o催化剂的排气系统 - Google Patents

具有在egr回路中的n2o催化剂的排气系统 Download PDF

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Publication number
CN106414983B
CN106414983B CN201580011052.1A CN201580011052A CN106414983B CN 106414983 B CN106414983 B CN 106414983B CN 201580011052 A CN201580011052 A CN 201580011052A CN 106414983 B CN106414983 B CN 106414983B
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catalyst
exhaust system
reducing
egr
reducing catalyst
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CN201580011052.1A
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CN106414983A (zh
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G·R·钱德勒
A·N·M·格林
P·R·菲利普斯
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Johnson Matthey PLC
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Johnson Matthey PLC
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/35—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with means for cleaning or treating the recirculated gases, e.g. catalysts, condensate traps, particle filters or heaters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
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    • B01D53/9413—Processes characterised by a specific catalyst
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    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
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    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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    • B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
    • B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/32—Manganese, technetium or rhenium
    • B01J23/34—Manganese
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    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
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    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F01N3/0231—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using special exhaust apparatus upstream of the filter for producing nitrogen dioxide, e.g. for continuous filter regeneration systems [CRT]
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Abstract

公开了一种用于内燃机的排气系统。该排气系统包含颗粒过滤器、一个或多个NOx还原催化剂和排气再循环(EGR)回路，该EGR回路用于将该排气系统在该过滤器和该一个或多个NOx还原催化剂的下游连接到该发动机的进气口。该EGR回路包含N2O生成催化剂。

Description

具有在EGR回路中的N2O催化剂的排气系统
技术领域
本发明涉及包含具有N2O生成催化剂的排气再循环(EGR)回路的排气系统。
背景技术
内燃机产生包含多种污染物的废气，污染物包括烃、颗粒物、硫氧化物、一氧化碳和氮氧化物(“NOx”)，氮氧化物包括一氧化氮(NO)、二氧化氮(NO2)、和氧化二氮(N2O)。日益严厉的国家和地区法规已经下调了从这种柴油或汽油发动机排出的污染物的数量。多种不同的技术已经被应用于排气系统，以在废气到达大气之前对其进行净化。
排气再循环(EGR)是一种通过经空气吸气口将一部分发动机废气返回到发动机燃烧室，来减少发动机的NOx排放的方法。EGR通过降低燃烧室中的氧气浓度，由此降低燃料燃烧火焰的峰值温度以及通过吸收热量来起作用。从1970年代中期开始EGR已经被使用在汽油燃料客车发动机中。随着汽油的应用，EGR 也被引入柴油客车，和从2000年代最初几年开始，引入重型柴油发动机。
一般地，有两种包含EGR的排气系统布置：(i)高压环路EGR，其中废气从涡轮增压器的上游被再循环；和(ii)低压环路EGR(也被称作长环路EGR)，其中废气经常从颗粒物过滤器的下游被再循环，允许所有废气被用于涡轮中。过滤器下游的废气压力一般低于进气歧管处，允许废气从过滤器流到进气歧管。
EGR系统的使用已经在例如PCT国际申请WO2012/120347中被教导，其公开了一种用于机动车贫燃内燃机的排气系统，该排气系统包含用于将排气系统在过滤器的下游连接到发动机的空气入口的低压EGR回路，其中EGR回路包含氨氧化催化剂。此外，PCT国际申请WO2012/114187教导了一种用于机动车贫燃内燃机的排气系统，该排气系统包含具有NOx吸附剂催化剂(NAC)的低压EGR回路，该NOx吸附剂催化剂包含一氧化氮(NO)吸附剂。
对任何汽车系统和过程而言，期望在排气处理系统中获取更进一步的改进。已经发现了一种新系统，其在EGR回路内利用N2O生成催化剂，以提高燃烧过程中的氧原子可用性，从而减少不期望的柴油颗粒物的数量。
发明内容
本发明是一种用于内燃机的排气系统。排气系统包含颗粒物过滤器、一个或多个NOx还原催化剂和排气再循环(EGR)回路，该EGR回路用于将排气系统在过滤器和一个或多个NOx还原催化剂的下游连接到发动机的进气口。该EGR回路适合于低压排气再循环。优选低压排气再循环(EGR)回路。
EGR回路包含N2O生成催化剂。在EGR回路内生成的N2O将提高发动机内用于燃烧过程的氧原子的可用性，从而使不期望的柴油颗粒物在数量上的减少。
附图说明
图1是本发明一个实施方案的示意流程图。
具体实施方式
本发明的排气系统包含颗粒物过滤器、一个或多个NOx还原催化剂和低压排气再循环(EGR)回路。
合适的NOx还原催化剂包括贫燃NOx捕集器。NOx捕集器(例如贫燃NOx捕集器) 是在贫燃排气条件下吸附NOx、在富燃条件下释放被吸附的NOx，和将被释放的 NOx还原形成N2的装置。
NOx捕集器(例如贫燃NOx捕集器)典型地包含用于存储NOx的NOx吸附剂和氧化/还原催化剂。典型地，在氧化催化剂存在下，一氧化氮与氧气反应生成NO2。其次，NO2以无机硝酸盐的形式被NOx吸附剂吸附(例如，BaO或BaCO3在NOx吸附剂上被转换成Ba(NO3)2)。最后，当发动机运行在富燃条件下，被存储的无机硝酸盐分解形成NO或NO2，然后在还原催化剂存在下它们通过与一氧化碳、氢气和/或烃的反应(或者通过NHx或NCO中间产物)被还原以形成N2。典型地，在废气流中，在热量、一氧化碳和烃存在下，氮氧化物被转换成氮气、二氧化碳和水。
NOx吸附剂成分优选是碱土金属(Ba、Ca、Sr和Mg)、碱金属(比如K、Na、 Li和Cs)、稀土金属(比如La、Y、Pr和Nd)或者它们的组合。这些金属典型地以氧化物的形式存在。氧化/还原催化剂优选地是一种或多种贵金属，更优选地是铂、钯和/或铑。优选地，包含铂以实现氧化功能，包含铑以实现还原功能。为了在排气系统中使用，氧化/还原催化剂和NOx吸附剂优选地负载在载体材料上如无机氧化物上。
合适的NOx还原催化剂也包括选择催化还原(SCR)催化剂。SCR催化剂是通过与氮化合物(如氨或尿素)或烃(贫燃NOx还原)反应，将NOx还原成N2的催化剂。优选地，SCR催化剂包含氧化钒-二氧化钛催化剂、氧化钒-氧化钨-二氧化钛催化剂或过渡金属/分子筛催化剂。过渡金属/分子筛催化剂包含过渡金属和分子筛，如铝硅酸盐分子筛或硅铝磷酸盐分子筛。
优选地，过渡金属选自铬、铈、锰、铁、钴、镍和铜及其任意两种或多种的混合物。特别优选铁或铜。
分子筛优选是β沸石、八面沸石(如X-沸石或Y-沸石，包括NaY和USY)、 L-沸石、ZSM沸石(例如ZSM-5、ZSM-48)、SSZ-沸石(例如SSZ-13、SSZ-41、 SSZ-33)、镁碱沸石、丝光沸石、菱沸石、钾沸石、毛沸石、斜发沸石、硅质岩、磷酸铝沸石(包括金属铝磷酸盐，如SAPO-34)、介孔沸石(例如MCM-41、MCM-49、 SBA-15)或其混合物；更优选地，分子筛是β沸石、镁碱沸石或菱沸石。优选的 SCR催化剂包括Cu-CHA，如Cu-SAPO-34、Cu-SSZ-13和Fe-β沸石。
NOx还原催化剂优选是SCR催化剂。
NOx还原催化剂优选被涂覆在陶瓷或金属基底上。该基底典型地经设计以提供大量的机动车废气流过的通道，这些通道的表面将优选地涂覆有NOx还原催化剂。
陶瓷基底可以由任意合适的难熔材料制成，例如氧化铝、二氧化硅、二氧化钛、氧化铈、氧化锆、氧化镁、沸石、氮化硅、碳化硅、锆硅酸盐、镁硅酸盐、铝硅酸盐和金属铝硅酸盐(如堇青石和锂辉石)或其任意两种或多种的混合物或混合氧化物。特别优选堇青石、铝硅酸镁和碳化硅。
金属基底可以由任意合适的金属制成，尤其是耐热金属和金属合金如钛和不锈钢，以及包含铁、镍、铬和/或铝以及其他痕量金属的铁素体合金。
用于NOx还原催化剂的基底可以是过滤器基底或流通式基底。优选地，NOx还原催化剂被涂覆到过滤器(例如过滤器基底)上。当NOx还原催化剂是SCR催化剂时，SCR催化剂和过滤器的组合被称为选择性催化还原过滤器(SCRFTM催化剂)。 SCRFTM催化剂是一种组合了SCR和颗粒过滤器的功能的单基底装置。
当NOx还原催化剂是SCR催化剂时，排气系统优选地包括用于将含氮还原剂引入SCR催化剂上游的排气系统中的装置。优选的是，用于将含氮还原剂引入排气系统中的装置位于SCR催化剂的直接上游(例如，在用于引入含氮还原剂的装置和SCR催化剂之间没有中间催化剂)。
还原剂通过任意合适的用于将还原剂引入废气的装置被添加到流动废气。合适的装置包括喷射器、喷洒器或进料器，优选是喷射器。这样的装置在现有技术中是已知的。
在系统中使用的含氮还原剂可以是氨本身、肼或选自以下的氨前体：尿素 ((NH2)2CO)、碳酸铵、氨基甲酸铵、碳酸氢铵和甲酸铵。特别优选尿素。
排气系统还可以包含用于控制将还原剂引入排气中以减少其中的NOx的装置。优选的控制装置包含电子控制单元，任选地是发动机控制单元，可以进一步包含位于NO还原催化剂的下游的NOx传感器。
本发明的排气系统还包含颗粒过滤器。颗粒过滤器优选是壁流式过滤器。
过滤器和NOx还原催化剂能以任意合适的构造布置。例如，NOx还原催化剂可以位于过滤器的下游。NOx还原催化剂可以位于过滤器的直接下游(例如，在过滤器和NOx还原催化剂之间没有中间催化剂)。
如果使用用于引入含氮还原剂的装置，当NOx还原催化剂是SCR催化剂时，用于将还原剂引入流动废气的装置合适地位于过滤器和SCR催化剂之间。
优选地，NOx还原催化剂位于颗粒过滤器上，最优选地以选择性催化还原过滤器(SCRFTM催化剂)的形式。在过滤器是壁流式过滤器的情况下，NOx还原催化剂可以经配制为渗入过滤器的壁的载体涂层(washcoat)。例如，这能通过将催化剂研磨成平均粒度≤5μm来实现。
优选地，排气系统将包含用于将NO氧化成二氧化氮的NO氧化催化剂(例如柴油氧化催化剂)。NO氧化催化剂优选地相对于废气流过系统的方向位于过滤器和/或NOx还原催化剂的上游，如直接上游。NO氧化催化剂优选地包含铂族金属，最优选地是铂。
排气系统还可以包含相对于废气流过系统的方向位于NOx还原催化剂的下游且在EGR的上游的氨氧化催化剂(或“氨泄漏催化剂”)。
优选地，氨氧化催化剂包含铂、钯或其组合，优选铂或铂/钯组合。
优选地，氨氧化催化剂包含负载在金属氧化物上的铂和/或钯，更优选地是大表面积载体，包括但不限于氧化铝。
氨氧化催化剂可以被施用到流通式整料基底，如流通式金属或堇青石蜂窝体，但优选地装载到与NOx还原催化剂相同的基底上，其中相对于废气流过系统的方向，上游区域载有NOx还原催化剂，和下游区域载有氨氧化催化剂。
因此，在低压EGR回路之前，排气系统的优选实施方案可以包括多种不同的构造，包括：(1)柴油氧化催化剂(DOC)，然后是颗粒过滤器，然后是用于引入含氮还原剂的装置，然后是SCR催化剂；或者(2)DOC，用于引入含氮还原剂的装置，然后是选择性催化还原过滤器(SCRFTM催化剂)，然后是SCR催化剂；或者(3)DOC，然后是选择性催化还原过滤器(SCRFTM催化剂)，然后是氨氧化催化剂；以及其他可行的组合。
该系统包含用于将排气系统在过滤器和NOx还原催化剂的下游连接到发动机的进气口的低压排气再循环(EGR)回路。
EGR回路包含N2O生成催化剂。N2O生成催化剂使EGR回路中的NH3与NO2反应，以产生N2O。任何将NH3和NO2转换成N2O的催化剂都是合适的。优选的N2O 生成催化剂包含负载在无机氧化物上的锰，但是也可以包含负载在无机氧化物上的任意其他过渡金属。
无机氧化物最常见地包含第2、3、4、5、13和14族元素的氧化物。有用的无机氧化物优选地具有10-700m2/g的表面积，0.1-4mL/g的孔体积，和约 10-1000埃的孔径。
无机氧化物优选是氧化铝、二氧化硅、二氧化钛、氧化锆、氧化铌、氧化钽、氧化钼、氧化钨、稀土氧化物(尤其是氧化铈或氧化钕)或其任意两种或多种的混合氧化物或复合氧化物，例如二氧化硅-氧化铝、氧化铈-氧化锆或氧化铝-氧化铈-氧化锆。无机氧化物也可以是沸石。
N2O生成催化剂优选地通过以任意已知的手段向无机氧化物添加锰化合物 (如醋酸锰)来制备，添加的方式不被认为是特别关键的。例如，锰化合物可以通过浸渍、吸附、离子交换、初湿浸渍、沉淀等添加到无极氧化物，以生产N2O 生成催化剂。
N2O生成催化剂优选地位于流通式整料基底之中或之上。
流通式基底优选地是陶瓷或金属基底。特别地，流通式基底是优选地具有蜂窝体结构的流通式整料，带有很多轴向延伸穿过基底并扩展遍布基底的小的平行的薄壁通道。基底的通道横截面可以是任意形状，但优选是正方形、正弦形、三角形、矩形、六边形、梯形、圆形或椭圆形。
陶瓷基底可以由任意合适的难熔材料制成，例如氧化铝、二氧化硅、二氧化钛、氧化铈、氧化锆、氧化镁、沸石、氮化硅、碳化硅、锆硅酸盐、镁硅酸盐、铝硅酸盐和金属铝硅酸盐(如堇青石和锂辉石)或其任意两种或多种的混合物或混合氧化物。特别优选堇青石、铝硅酸锰和碳化硅。金属基底可以由任意合适的金属制成，尤其是耐热金属和金属合金如钛和不锈钢，以及包含铁、镍、铬和/或铝以及其他痕量金属的铁素体合金。
优选地，N2O生成催化剂通过任意已知的受到被涂覆到流通式基底上，更优选地N2O生成催化剂利用载体涂层程序被沉积在基底上。
载体涂覆(washcoating)优选地通过首先在恰当的溶剂、优选水中，将N2O 生成催化剂的磨碎的颗粒制浆以形成浆料来进行。浆料优选地含有5-70重量％的固体，更优选地10-50重量％。
优选地，N2O生成催化剂颗粒被研磨或者经受另一粉碎处理，以保证在形成浆料之前，基本上所有的固体颗粒具有小于20微米的粒度。
另外的成分如稳定剂或促进剂也可以被并入浆料，作为水溶性或水分散性化合物或络合物的混合物。
基底可以利用浆料被涂覆一次或多次，从而使在基底上沉积所需量的催化材料。经涂覆的基底典型地被干燥，然后通过在升高的温度加热来煅烧。优选地，煅烧在400-600℃发生约1-8小时。
图1显示了本发明的一个实施方案，显示了设备的截面图。该设备包含发动机10和排气系统12。该排气系统包含将发动机连接到任选的柴油氧化催化剂 (DOC)16的导管14。来自发动机10的废气流到任选的DOC 16，然后流到选择性催化还原过滤器(SCRFTM催化剂)20，然后流到任选的氨氧化催化剂22。任选的含氮还原剂装置18被用于向流入选择性催化还原过滤器(SCRFTM催化剂)20 的废气添加含氮还原剂如尿素。低压排气再循环回路26包含排气再循环阀24。位于EGR回路26内的N2O生成催化剂28被用于在EGR回路中转换NH3和NO2，以产生N2O，然后N2O被供回发动机10的进气口30。

Claims (11)

1.用于内燃发动机的排气系统，该系统包含颗粒物过滤器、一个或多个NOx还原催化剂和低压排气再循环(EGR)回路，该EGR回路用于将该排气系统在该过滤器和该一个或多个NOx还原催化剂的下游连接到该发动机的进气口，其中该EGR回路包含N2O生成催化剂，其中该N2O生成催化剂包含负载在无机氧化物上的锰。
2.根据权利要求1所述的排气系统，其中NOx还原催化剂或该一个或多个NOx还原催化剂位于该过滤器上。
3.根据权利要求1所述的排气系统，其中NOx还原催化剂或该一个或多个NOx还原催化剂是选择性催化还原催化剂。
4.根据权利要求3所述的排气系统，其中该选择性催化还原催化剂包含过渡金属和分子筛。
5.根据权利要求3或4所述的排气系统，还包含用于将含氮还原剂在该选择性催化还原催化剂的上游引入该排气系统的装置。
6.根据权利要求5所述的排气系统，其中该含氮还原剂是氨、肼或者选自以下的氨前体：尿素((NH2)2CO)、碳酸铵、氨基甲酸铵、碳酸氢铵和甲酸铵。
7.根据权利要求1所述的排气系统，其中NOx还原催化剂或该一个或多个NOx还原催化剂是贫燃NOx捕集器。
8.根据权利要求1所述的排气系统，其中该N2O生成催化剂位于流通式整料基底之中或之上。
9.根据权利要求1所述的排气系统，还包含位于该颗粒物过滤器的上游的NO氧化催化剂。
10.根据权利要求1所述的排气系统，还包含氨氧化催化剂，该氨氧化催化剂相对于废气流过该系统的方向位于该一个或多个NOx还原催化剂的下游和该EGR的上游。
11.根据权利要求10所述的排气系统，其中NOx还原催化剂和该氨氧化催化剂被装载到同一个基底上，其中前部载有该NOx还原催化剂，和后部载有该氨氧化催化剂。
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