CN112246251B - 一种天然气汽车尾气净化催化剂及其制备方法 - Google Patents

一种天然气汽车尾气净化催化剂及其制备方法 Download PDF

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CN112246251B
CN112246251B CN202011216149.5A CN202011216149A CN112246251B CN 112246251 B CN112246251 B CN 112246251B CN 202011216149 A CN202011216149 A CN 202011216149A CN 112246251 B CN112246251 B CN 112246251B
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沈谱清
钟琳
陈耀强
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Sichuan University
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Abstract

本发明公开了一种天然气汽车尾气净化催化剂及其制备方法。制备方法包括：La0.67Fe0.83Cu0.17O3钙钛矿的制备，Pd/Al2O3材料的制备，整体式催化剂的制备；催化剂成分包含Pd/Al2O3催化剂和钙钛矿以10～3:1的比例球磨混合，钙钛矿通过溶胶凝胶法制得，主要成为La0.67Fe0.83Cu0.17O3。在理论空燃比条件1000ppm CH4、5000ppm CO、930ppm NO、4035ppmO2、10vol.％CO2,5vol.％H2O、N2作为平衡气，空速为54000h‑1进行活性测试，在300～500℃程序升温过程中，发现尾气中氨的含量一直维持在10ppm以下。本发明方法制备的催化剂可以减少天然气汽车尾气中氨的含量，同时显著降低尾气中其他有害成分甲烷、一氧化碳、氮氧化合物的含量。

Description

一种天然气汽车尾气净化催化剂及其制备方法
技术领域
本发明属于催化剂研究制备技术领域，尤其属于汽车尾气净化催化剂研究制备技术领域，特别涉及一种天然气汽车尾气净化催化剂及其制备方法。
背景技术
典型的天然气汽车废气是含有气体排放物一氧化碳(CO)、未燃烧的甲烷(CH4)和氮氧化物(NOx)等成分的不均匀混合物。通常，在发动机的排气系统中安装的催化剂已经将绝大部分废气组分转化成无害组分。例如目前使用最广泛的三效催化剂(TWC)可以显著减少一氧化碳(CO)、烃(HC)和氮氧化物(NOx)的排放，但三效催化剂的使用会使发动机中的NOx部分转化为氨 (NH3)并作为二次排放物排出。
目前最新的重型柴油车污染物排放限制及测量方法(中国第六阶段) 已经规定了重型车的NH3的排放限制(10ppm以下)，为了满足现有的国六标准，现有的技术基本是在发动机排气系统中额外增加一个氨氧化催化装置 (ASC)，这样的话也会适当增加一定的生产成本，除此之外目前国内并没有其他有效的方法解决机动车尾气中氨排放的问题。因此找出可以显著降低尾气中的NOx、HC和CO含量同时将NH3的排放值将至最低的催化剂是很有必要的。
发明内容
本发明根据现有技术的不足公开了一种天然气汽车尾气净化催化剂及其制备方法。本发明目的是提供一种能够有效净化天然气汽车尾气中的NOx、 HC和CO，同时将NH3的排放值净化至最低的催化剂及其制备方法。
本发明通过以下技术方案实现：
本发明公开一种天然气汽车尾气净化催化剂的制备方法。
La0.67Fe0.83Cu0.17O3钙钛矿的制备：
(1)按照上述钙钛矿的化学成分称取相应比例的前驱体盐 La(NO3)3·6H2O、Fe(NO3)3·9H2O、Cu(NO3)2·2H2O充分溶解在去离子水中；
(2)将步骤(1)所得溶液加入等摩尔质量的柠檬酸加热搅拌溶解后在98℃水浴条件下搅拌直至蒸干水分；
(3)将步骤(2)所得的样品在马弗炉中200℃下焙烧1h，之后在600℃下焙烧8h得到钙钛矿化合物La0.67Fe0.83Cu0.17O3；
Pd/Al2O3材料的制备：
(4)按Pd在Pd/Al2O3材料中的质量百分比1.5wt％称取硝酸钯，将硝酸钯溶解，采用等孔体积浸渍法浸渍Al2O3粉末，干燥，在马弗炉中550℃焙烧3h得到Pd/Al2O3粉末；
整体式催化剂的制备：
(5)将所得的La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3粉末按质量比3～10:1 混合，再与去离子水、粘接剂混合后球磨制成浆液，控制浆液的固含量在 40～45wt％；
(6)将步骤(5)制备的浆液均匀涂敷在载体堇青石陶瓷蜂窝基体或金属基体上，Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到Pd/Al2O3-La0.67Fe0.83Cu0.17O3整体式催化剂。
与现有的技术比，本发明的有益效果：
本发明制备了钙钛矿化合物，在通过XRD检测确认制备出钙钛矿的结构之后，制备Al2O3负载1.5wt％Pd，将制备好的Pd/Al2O3和钙钛矿催化剂球磨混合制备得到本发明天然气汽车尾气净化催化剂。检测结果表明：本发明具有优异的净化天然气汽车尾气中的NOx、HC和CO的效率，同时可以显著降低尾气中NH3的含量；本发明催化剂将Pd/Al2O3直接球磨混合添加 La0.67Fe0.83Cu0.17O3钙钛矿，制备方法简洁、分别，制备的催化剂能够达到明显的氨抑制效果，能够很大程度节约催化剂制备成本。
附图说明
图1是制备的La0.67Fe0.83Cu0.17O3的XRD图谱，根据标准的LaFeO3卡片对比可知得出了钙钛矿的结构。
图2是五种催化剂(Pd/Al2O3、La0.67Fe0.83Cu0.17O3、10Pd/Al-LaFeCu、 5Pd/Al-LaFeCu、3Pd/Al-LaFeCu)对于甲烷的活性图，反应气成分为1000ppm CH4,5000ppm CO,930ppm NO,4035ppm O2,10vol.％CO2,5vol.％H2O，N2为平衡气，空速为54000h-1。
图3是五种催化剂(Pd/Al2O3、La0.67Fe0.83Cu0.17O3、10Pd/Al-LaFeCu、 5Pd/Al-LaFeCu、3Pd/Al-LaFeCu)对于一氧化氮的活性图，反应气成分为1000ppm CH4,5000ppm CO,930ppm NO,4035ppm O2,10vol.％CO2,5vol.％H2O， N2为平衡气，空速为54000h-1。
图4是五种催化剂(Pd/Al2O3、La0.67Fe0.83Cu0.17O3、10Pd/Al-LaFeCu、 5Pd/Al-LaFeCu、3Pd/Al-LaFeCu)对于一氧化碳的活性图，反应气成分为 1000ppm CH4,5000ppmCO,930ppm NO,4035ppm O2,10vol.％CO2,5vol.％H2O， N2为平衡气，空速为54000h-1。
图5是五种催化剂(Pd/Al2O3、La0.67Fe0.83Cu0.17O3、10Pd/Al-LaFeCu、 5Pd/Al-LaFeCu、3Pd/Al-LaFeCu)尾气中氨的含量，反应气成分为1000ppm CH4,5000ppm CO,930ppmNO,4035ppm O2,10vol.％CO2,5vol.％H2O，N2为平衡气，空速为54000h-1。
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。
实施例1
La0.67Fe0.83Cu0.17O3钙钛矿的制备：
(1)称取29.012g(La(NO3)3·6H2O、33.532g Fe(NO3)3·9H2O、 4.107Cu(NO3)2·2H2O用60ml去离子水充分溶解。
(2)将步骤(1)所得溶液加入等摩尔质量的柠檬酸加热搅拌溶解后在98℃水浴条件下搅拌12h直至蒸干水分。
(3)将步骤(2)所得的样品在马弗炉中200℃下焙烧1h,之后在600℃下焙烧8h即可得到钙钛矿化合物La0.67Fe0.83Cu0.17O3。
Pd/Al2O3材料的制备：
(4)将硝酸钯溶液(1.5wt％Pd)适当稀释，采用等孔体积浸渍法浸渍Al2O3粉末，干燥，在马弗炉中550℃焙烧3h得到Pd/Al2O3粉末催化剂。
整体式催化剂的制备：
将所得的La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3催化剂按质量比10:1混合，在与去离子水、粘接剂混合均匀球磨制成浆液，控制浆液的固含量在 40％-45％，均匀涂敷在Φ11mm*25mm/400cpsi堇青石陶瓷蜂窝基体上，控制 Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到10Pd/Al2O3-La0.67Fe0.83Cu0.17O3整体式催化剂。
实施例2
与实施例1的相同步骤制备La0.67Fe0.83Cu0.17O3钙钛矿和Pd/Al2O3材料。
整体式催化剂的制备：
将所得的La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3催化剂按质量比5:1混合，在与去离子水、粘接剂混合均匀球磨制成浆液，控制浆液的固含量在 40％-45％，均匀涂敷在Φ11mm*25mm/400cpsi堇青石陶瓷蜂窝基体上，控制 Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到5Pd/Al2O3-La0.67Fe0.83Cu0.17O3整体式催化剂。
实施例3
与实施例1的相同步骤制备La0.67Fe0.83Cu0.17O3钙钛矿和Pd/Al2O3材料。
整体式催化剂的制备：
将所得的La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3催化剂按质量比3:1混合，在与去离子水、粘接剂混合均匀球磨制成浆液，控制浆液的固含量在40％-45％，均匀涂敷在Φ11mm*25mm/400cpsi堇青石陶瓷蜂窝基体上，控制 Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到3Pd/Al2O3-La0.67Fe0.83Cu0.17O3整体式催化剂。
对比例1
Pd/Al2O3整体式催化剂的制备：
将步骤(4)所得的Pd/Al2O3与去离子水、粘接剂混合均匀制成浆液，控制浆液的固含量在40％-45％，均匀涂敷在Φ11mm*25mm/400cpsi堇青石陶瓷蜂窝基体上，控制Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中 550℃焙烧3h，即可得到Pd/Al2O3整体式催化剂。
对比例2
与实施例1的相同步骤制备La0.67Fe0.83Cu0.17O3钙钛矿。
La0.67Fe0.83Cu0.17O3整体式催化剂的制备：
将所得的La0.67Fe0.83Cu0.17O3粉末和去离子水、粘接剂混合均匀制成浆液，控制浆液的固含量在40％-45％，均匀涂敷在Φ11mm*25mm/400cpsi堇青石陶瓷蜂窝基体上，控制催化剂涂层上载量为160g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到La0.67Fe0.83Cu0.17O3整体式催化剂。
活性评价实验：
催化剂的活性评价在多路固定连续流动的微型反应器中进行，模拟天然气汽车尾气组分为：1000ppm CH4,5000ppm CO,930ppm NO,4035ppm O2, 10vol.％CO2,5vol.％H2O，N2为平衡气，空速为54000h-1。所有催化剂样品在反应前均在反应气氛中500摄氏度预处理1h。然后以5℃/min的升温速率测试，以300℃为起始温度进行活性测试，每10℃记录一次活性。CH4、 CO、NO、NH3的浓度采用傅里叶红外分析仪进行测试。最终得到的活性评价结果如下图2、3、4、5所示。
通过图2的活性结果可以看出CH4在Pd/Al2O3催化剂上可以在450℃左右达到100％的转化率，CH4在钙钛矿催化剂上基本是没有活性的，对于 Pd/Al2O3和钙钛矿的混合物CH4的转化率可以在500℃左右最高达到88％。可以看出混合物对于CH4的活性是比较好的。
通过图3的活性结果可以看出NO在Pd/Al2O3催化剂上可以在440℃达到100％转化率，NO在钙钛矿催化剂上的活性很低，对于Pd/Al2O3和钙钛矿的混合物CH4的转化率可以在500℃左右达到100％。可以看出混合物对于NO 的活性是比较好的。
通过图4的活性结果可以看出CO在三种催化剂上300℃时均可以达到 100％的转化率，但对于Pd/Al2O3、10Pd/Al-LaFeCu、5Pd/Al-LaFeCu催化剂在400℃以后CO的活性出现了略微的下降，其他两个催化剂在300-500℃均达到了100％转化率。可以看出钙钛矿的加入可以促进高温段CO转化率。
图5是五种催化剂尾气中氨的含量，可以看出Pd/Al2O3催化剂在400℃以后NH3的含量在逐渐上升，在500℃时已经达到200ppm，可以看出随着钙钛矿的加入，可以明显抑制氨的生成，且加入的量越多，氨的抑制效果就越好。当Pd/Al2O3和钙钛矿质量比为3:1时，可以达到最佳的抑制效果 (<10ppm)，符合国六标准。
通过几种活性图对比可知，La0.67Fe0.83Cu0.17O3钙钛矿和传统的贵金属催化剂相比是可以显著降低尾气中NH3的含量的，加入的La0.67Fe0.83Cu0.17O3越多，对氨的抑制效果越明显，从图5可以看出本发明实施例三氨的抑制效果最好。对于Pd/Al2O3和钙钛矿混合物不仅可以显著降低尾气中NH3的含量，对于CH4，NO和CO都有较好的活性，同时对于CO的活性，Pd/Al2O3一般在高温过后转化率会有一定下降，而钙钛矿，Pd/Al2O3和钙钛矿的混合物在高温时CO转化率然可以达到100％。
目前机动车尾气中氨抑制的主要方法为在尾气净化装置中额外增加一个ASC催化剂，这样会明显增加成本。本发明的优势在于在直接添加 La0.67Fe0.83Cu0.17O3钙钛矿就可以达到很明显的氨抑制效果，可以很大程度节约成本。

Claims (5)

1.一种天然气汽车尾气净化催化剂制备方法，其特征在于包括以下步骤：
La0.67Fe0.83Cu0.17O3钙钛矿的制备：
(1)按照上述钙钛矿的化学成分称取相应比例的前驱体盐La(NO3)3·6H2O、Fe(NO3)3·9H2O、Cu(NO3)2·2H2O充分溶解在去离子水中；
(2)将步骤(1)所得溶液中加入与前驱体盐等摩尔质量的柠檬酸加热搅拌溶解后在98℃水浴条件下搅拌直至蒸干水分；
(3)将步骤(2)所得的样品在马弗炉中200℃下焙烧1h，之后在600℃下焙烧8h得到钙钛矿化合物La0.67Fe0.83Cu0.17O3；
Pd/Al2O3材料的制备：
(4)按Pd在Pd/Al2O3材料中的质量百分比1.5wt％称取硝酸钯，将硝酸钯溶解，采用等孔体积浸渍法浸渍Al2O3粉末，干燥，在马弗炉中550℃焙烧3h得到Pd/Al2O3粉末；
整体式催化剂的制备：
(5)将所得的La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3粉末按质量比3～10:1混合，再与去离子水、粘接剂混合后球磨制成浆液，控制浆液的固含量在40～45wt％；
(6)将步骤(5)制备的浆液均匀涂敷在载体堇青石陶瓷蜂窝基体或金属基体上，Pd的上载量为1.7g/L，在120℃干燥8h，在马弗炉中550℃焙烧3h，即可得到Pd/Al2O3-La0.67Fe0.83Cu0.17O3整体式催化剂。
2.根据权利要求1所述的天然气汽车尾气净化催化剂制备方法，其特征在于：所述步骤(5)中La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3粉末质量比是3:1。
3.根据权利要求1所述的天然气汽车尾气净化催化剂制备方法，其特征在于：所述步骤(5)中La0.67Fe0.83Cu0.17O3粉末和Pd/Al2O3粉末球磨混合的时间为10min。
4.根据权利要求1所述的天然气汽车尾气净化催化剂制备方法，其特征在于：所述步骤(6)中载体是堇青石陶瓷蜂窝基体。
5.一种天然气汽车尾气净化催化剂，其特征在于：所述催化剂是权利要求1至4任一项所述方法制备的天然气汽车尾气净化催化剂。
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