CN110215932B - 一种用于汽车尾气净化的低温NOx存储催化剂及其制备方法 - Google Patents

一种用于汽车尾气净化的低温NOx存储催化剂及其制备方法 Download PDF

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CN110215932B
CN110215932B CN201910515807.1A CN201910515807A CN110215932B CN 110215932 B CN110215932 B CN 110215932B CN 201910515807 A CN201910515807 A CN 201910515807A CN 110215932 B CN110215932 B CN 110215932B
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noble metal
temperature
molecular sieve
coating
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CN110215932A (zh
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王云
徐海迪
淡宜
程永香
张志风
董银华
陈德权
陈耀强
李云
陈启章
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Zhongzi Technology Co ltd
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Sinocat Environmental Technology Co Ltd
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Abstract

本发明公开了一种用于汽车尾气净化的低温NOx存储催化剂及其制备方法。将贵金属盐溶液以等体积浸渍法负载到分子筛上，贵金属包含硝酸钯和硝酸铂，分子筛包含SSZ、SAPO和BETA；在60‑120℃干燥2‑6h，在500‑550℃温度下，空气气氛中焙烧2‑5h，继续在750‑850℃温度下，空气气氛中焙烧2‑5h，再与铝溶胶混合，球磨制浆后涂覆于载体上，上载量100‑250g/L，贵金属含量10‑150g/ft3，在60‑120℃干燥2‑6h，500‑550℃空气气氛中焙烧2‑5h，750‑850℃空气气氛中焙烧2‑5h，得到催化剂。本发明将贵金属Pt和Pd负载到分子筛孔道内，选用不同类型的分子筛作为NOx存储单元，提高Pt和Pd负载的分子筛粉料和催化剂的焙烧温度后，NOx存储量显著增加。

Description

一种用于汽车尾气净化的低温NOx存储催化剂及其制备方法
技术领域
本发明属于催化剂制备技术领域，尤其属于汽车尾气催化剂制备技术领域，特别涉及一种用于汽车尾气净化的低温NOx存储催化剂及其制备方法。
背景技术
重型发动机排放测试循环从国五的ETC循环升级到国六的WHTC循环。柴油发动机WHTC冷态循环中，至少需要400s，SCR入口温度才能达到200 ℃以上，此时才开始喷尿素，并通过SCR将NOx还原为N2，部分冷启动阶段排放较差的发动机，冷启动阶段的排放可能已接近法规限值。天然气发动机WHTC冷启动循环中，至少需要250s，TWC入口温度才能达到300℃以上，此时TWC对NOx才开始转化。此外，重型车在国VI b阶段，增加了整车PEMS 测试，尾气平均温度低于发动机WHTC循环排温。因此，冷启动阶段的NOx 排放将成为国六阶段，特别是国六b阶段的难点之一。
解决汽车在冷启动阶段NOx排放的方法之一是在汽车排气管上增加一个NOx吸附催化剂。传统地，NOx吸附催化剂主要以分子筛为主。不同类型的分子筛对NOx的吸附和存储量有较大差异，适用于汽车尾气条件下的NOx吸附和存储的分子筛有SAPO、BETA、SSZ等。在分子筛材料中加入一定量的贵金属或过渡金属可提高NOx的吸附量，其中加入贵金属Pd或Pt对NOx吸附量的提高最显著。
发明内容
本发明的目的是提供一种低温NOx存储催化剂及其制备方法，该催化剂主要应用于重型柴油车或重型天然气车冷启动阶段NOx的净化。本发明的催化剂，在冷启动阶段，存储汽车排放的NOx，并在温度升高后，NOx释放，其中柴油车释放的NOx在下游SCR上反应；天然气车释放的NOx在下游TWC上反应，以净化低温排放的NOx。该催化剂涂层主要以分子筛为载体材料，贵金属为活性组分。活性组分包含但不限于Pt、Pd等贵金属元素。分子筛包含但不限于BETA、SAPO和SSZ等分子筛。
本发明研究了不同比例的Pt和Pd负载在SAPO-34分子筛上对NOx的存储量，结果显示，高Pt低Pd催化剂具有较高的NOx存储量。进一步地，对比了高Pt低Pd负载在SSZ-13和BETA分子筛上，结果显示，选用SSZ-13 作为吸附剂时，具有更高的NOx吸附量。进一步地，选择用高Pt低Pd负载的SSZ-13，对制备工艺进行优化，催化剂粉料和催化剂的焙烧温度从500℃提高至800℃，制备的催化剂对NOx的存储量进一步提高。
本发明采用的催化剂制备方法是，先将活性组分负载至分子筛材料上，然后干燥焙烧固化，最后制浆涂覆至堇青石基体上。该方法工艺简单，操作简便。
本发明通过以下技术方案实现：
(1)将贵金属盐溶液以等体积浸渍法负载到分子筛上，贵金属盐溶液包含但不限于硝酸钯和硝酸铂，分子筛包含但不限于SSZ、SAPO和BETA；贵金属以单质计，含量占涂层的质量百分数大于0％、小于等于3％，然后在60-120℃干燥2-6h，在500-550℃温度下，空气气氛中焙烧2-5h，进一步，继续在750-850℃温度下，空气气氛中焙烧2-5h，得到M1；
(2)将M1和铝溶胶混合，球磨制浆，得到贵金属浆料N1；
(3)将浆料N1涂覆于载体上，涂层上载量100-250g/L，贵金属含量 10-150g/ft3，在60-120℃干燥2-6h，然后在500-550℃，空气气氛中焙烧 2-5h，进一步，继续在750-850℃温度下，空气气氛中焙烧2-5h，得到催化剂。
在上述步骤中，所述的贵金属前驱体优选为硝酸铂和硝酸钯或其它可溶性盐。
上述步骤中，整体催化剂贵金属铂和钯比例优选为1:9-9:1。
上述分子筛是SSZ、SAPO或BETA中的一种或几种的混合物。
本发明有益性：本发明将贵金属Pt和Pd负载到分子筛孔道内，提高催化剂在低温时对NOx的存储量。
本发明根据不同类型发动机排温和原排的特点，选用不同类型的分子筛作为NOx存储单元。
本发明提高Pt和Pd负载的分子筛粉料和催化剂的焙烧温度后，NOx存储量显著增加。
本发明制备的贵金属基分子筛NOx存储催化剂，具有较大的NOx存储量，可以降低发动机匹配的催化剂体积。
本发明采用传统的等体积浸渍工艺和制浆工艺，工艺简便可行。
附图说明
图1是本发明不同实施例制备的催化剂NO相对存储量。
图中，纵坐标是NO相对吸附量，单位％；横坐标，C0是对比例催化剂， C1-C7是实施例1至7催化剂。
图2是本发明实施例6和实施例8制备的催化剂对NO相对存储量。
图中，纵坐标是NO相对存储量，单位％；横坐标，C6是实施6催化剂， C8是实施例8催化剂。
具体实施方式
下面结合具体实施方式对本发明进一步说明，具体实施方式是对本发明原理的进一步说明，不以任何方式限制本发明，与本发明相同或类似技术均没有超出本发明保护的范围。
对比例1
将SAPO-34与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量 45％的浆料N0。
将N0涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L。
将以上制备好的催化剂记为C0。
实施例1
将硝酸钯溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M1。
将M1与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N1。
将N1涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C1。
实施例2
将硝酸铂溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M2。
将M2与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N2。
将N2涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C2。
实施例3
将硝酸铂溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M3-1。
将硝酸钯溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M3-2。
将M3-1和M3-2以1：3混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N3。
将N3涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L,贵金属含量100g/ft3。
将以上制备好的催化剂记为C3。
实施例4
将硝酸铂溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M4-1。
将硝酸钯溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M4-2。
将M4-1和M4-2以3：1混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N4。
将N4涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C4。
实施例5
将硝酸铂溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M5-1。
将硝酸钯溶液，以等体积浸渍法负载到SAPO-34分子筛上，80℃干燥 6h，500℃焙烧2h，记为M5-2。
将M5-1和M5-2以1：1混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N5。
将N5涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C5。
实施例6
将硝酸铂溶液，以等体积浸渍法负载到SSZ-13分子筛上，80℃干燥 6h，500℃焙烧2h，记为M6-1。
将硝酸钯溶液，以等体积浸渍法负载到SSZ-13分子筛上，80℃干燥 6h，500℃焙烧2h，记为M6-2。
将M6-1和M6-2以3：1混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N6。
将N6涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C6。
实施例7
将硝酸铂溶液，以等体积浸渍法负载到BETA分子筛上，80℃干燥6h， 500℃焙烧2h，记为M7-1。
将硝酸钯溶液，以等体积浸渍法负载到BETA分子筛上，80℃干燥6h， 500℃焙烧2h，记为M7-2。
将M7-1和M7-2以3：1混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N7。
将N7涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，涂覆量150g/L,贵金属含量100g/ft3。
将以上制备好的催化剂记为C7。
实施例8
将硝酸铂溶液，以等体积浸渍法负载到SSZ-13分子筛上，80℃干燥6h，500℃焙烧2h，800℃焙烧2h，记为M8-1。
将硝酸钯溶液，以等体积浸渍法负载到SSZ-13分子筛上，80℃干燥 6h，500℃焙烧2h，800℃焙烧2h，记为M8-2。
将M6-1和M6-2以3：1混合，加入铝溶胶，球磨10min，粘接剂占比3％，得到固含量45％的浆料N8。
将N8涂覆至堇青石基体上，载体尺寸Φ25.4*101.6/400cpsi-4mil。经80℃干燥6h，500℃焙烧2h，800℃焙烧2h。涂覆量150g/L，贵金属含量100g/ft3。
将以上制备好的催化剂记为C8。
将上述实施例制备的催化剂进行活性评价试验，试验条件如下：
将催化剂在5％O2气氛下，程序升温至450℃，恒温1h，降温至25℃, 将实验气氛切换为5％NO，恒温30min，然后切换为N2，并以10℃/min，升温至450℃。实验中，以NO代替尾气中的NOx。各实施例和对比例对NO 的相对吸附量如图1所示。
从图1可以看出：
1)实施例C1和C2与对比例C0相比，分子筛相同，对比例C0未加入贵金属，C1和C2中分别负载贵金属Pd和Pt。分子筛中负载贵金属后，NO 的相对吸附量大幅增加。
2)实施例C1-C5，分子筛相同，贵金属及比例不同。C2相对于C1， NO的相对吸附量较高，因此，贵金属Pt作为活性组分较Pd对NO有更高的吸附量。C3-C5是不同Pt和Pd比例的催化剂，规律和C1、C2相同，Pt含量较高的C2和C4具有相对更高的吸附量。
3)实施例C6，相对于C4，贵金属及比例相同，分子筛不同。相对于 C4，C6分子筛从SAPO-34换为SSZ-13后，NO相对吸附量增加。
4)实施例C7，相对于C4，贵金属及比例相同，分子筛不同。相对于 C4，C7分子筛从SAPO-34换为BETA后，NO相对吸附量降低。
5)实施例C8，相对于C6，贵金属及比例相同，分子筛相同，主要区别是贵金属负载的分子筛粉料的焙烧温度不同。相对于C6，C8的粉料焙烧温度从500℃提高至800℃后，制备的催化剂对NO的相对吸附量进一步显著提高。
上述实验说明：a，分子筛中负载贵金属后，NO的存储量大幅增加；b，贵金属Pt比Pd负载在分子筛上，NO存储量相对更大；c，在负载相同贵金属的前提下，BETA、SAPO-34和SSZ-13三种分子筛对NO的存储量依次增大； d，提高贵金属负载的分子筛的焙烧温度，NO存储量进一步提高。

Claims (5)

1.一种用于汽车尾气净化的低温NOx存储催化剂制备方法，其特征在于包括以下步骤：
(1)将贵金属盐溶液以等体积浸渍法负载到分子筛上，贵金属盐溶液包含但不限于硝酸钯和硝酸铂，分子筛包含但不限于SSZ、SAPO和BETA；贵金属以单质计，含量占涂层的质量百分数大于0％、小于等于3％，然后在60-120℃干燥2-6h，在500-550℃温度下，空气气氛中焙烧2-5h，进一步，继续在750-850℃温度下，空气气氛中焙烧2-5h，得到M1；
(2)将M1和铝溶胶混合，球磨制浆，得到贵金属浆料N1；
(3)将浆料N1涂覆于载体上，涂层上载量100-250g/L，贵金属含量10-150g/ft3，在60-120℃干燥2-6h，然后在500-550℃，空气气氛中焙烧2-5h，进一步，继续在750-850℃温度下，空气气氛中焙烧2-5h，得到催化剂。
2.根据权利要求1所述的用于汽车尾气净化的低温NOx存储催化剂制备方法，其特征在于：所述步骤(1)中，贵金属盐溶液为铂、钯的可溶性盐溶液。
3.根据权利要求1所述的用于汽车尾气净化的低温NOx存储催化剂制备方法，其特征在于：所述催化剂中贵金属铂与钯的质量比例为1:9-9:1。
4.根据权利要求1所述的用于汽车尾气净化的低温NOx存储催化剂制备方法，其特征在于：所述分子筛是SSZ、SAPO或BETA中的一种或几种的混合物。
5.一种用于车辆尾气净化的低温NOx存储催化剂，其特征在于：催化剂是权利要求1至4任一项制备方法制备的催化剂。
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