CN108722464B - 一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂及其制备方法和应用 - Google Patents
一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂及其制备方法和应用 Download PDFInfo
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Abstract
本发明公开了一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂及其制备方法和应用,其是将Pd纳米粒子负载在具有光吸收的N‑TiO2半导体载体上,制得所述负载型Pd催化剂,TiO2半导体通过N掺杂引入了可见光,从而可利用光热耦合作用实现CO/NO的低温高效催化去除。本发明中引入非金属掺杂TiO2从而提高了所得催化剂在可见光下对CO与NO的去除,且以无毒绿色的N‑TiO2为半导体的催化剂有望制备成涂抹型,且其制备方法简单易行,更有利于推广应用。
Description
技术领域
本发明属于环境保护及空气净化领域,具体涉及一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂及其制备方法和应用,该负载型Pd催化剂可通过光热耦合作用提高对CO和NO的催化去除效果。
背景技术
自从上世纪70年代以来,环境污染的不断恶化,如酸雨问题、温室效应、臭氧层空洞问题和水质污染等,已经严重危害了人类的正常生活和身体健康。其中,在我国城市大气污染中,汽车尾气排放所占比例已超过70%,而汽车尾气的排放不仅给我们的生活、环境造成了极大的危害,同时对人体的健康也带来了不可忽视的伤害。而大气自我净化能力已不足以降解汽车尾气,因此,解决汽车尾气污染,还人类一个洁净的环境已迫在眉睫。
科学分析表明,汽车尾气中含有上百种不同的化合物,其中的污染物有固体悬浮微粒、一氧化碳、二氧化碳、碳氢化合物、氮氧化合物、铅及硫氧化合物等。对于汽车尾气排放量的控制,各国的政策都经历了一系列的变革,从最初的仅限制CO的排放,到限制CO和HCs的排放,到最后一体化的限制CO、HCs和氮氧化物NOx的排放;同时,在科学研究上,人们一直尝试从化学燃料、发动机燃烧效率、催化剂等各方面来控制汽车尾气中对大气污染较严重的气体,尤其是一氧化碳CO,碳氢化合物HCs和氮氧化物NOx。
治理汽车排气污染的技术手段主要可分为三类:一是机内净化技术,如燃油品质改善,曲轴箱强制通风系统,燃油蒸发回收系统,燃烧系统、供油系统和点火系统的改造,废气再循环,排气管内喷射二次空气,高能点火与稀薄燃烧等;二是机外净化,主要是在发动机机体外的某些方面进行处理,以达到降低汽车尾气排放的目的,就目前机外净化技术的发展情况而言,主要研究的方向是对汽车尾气的催化净化;三是使用清洁的替代燃料,如天然气、液化石油气或电能等。
在机内净化技术研发遇到瓶颈以及绿色能源暂时不能有效取代化石燃料的现状下,汽车尾气净化催化技术正得到日益广泛的应用。汽车尾气的催化净化装置是一种可以对汽车尾气进行整体上综合处理的装置,其一般安装在汽车排气系统中,采用催化原理来净化汽车尾气中的一氧化碳、氮氧化合物、碳氢化合物等有害物质。三效催化剂是汽车尾气三元催化转化器里使用的催化剂,它具有高活性、高选择性、高热稳定性、良好物理性能,能同时去除汽车尾气中的CO、HC和NOx等污染物,是较为理想的汽车尾气催化剂。三效催化剂的主要化学反应为:。其中,NO的还原反应难以进行是三效催化剂研究中的一个难点。
目前,有关三效催化剂催化去除CO/NO的研究已日趋成熟。三效催化剂主要包括载体和活性组分,载体一般为蜂窝状荃青石,而活性组分研究较多的是贵金属Pt、Pd、Rh,特别是有关Pd的催化剂出现了较多的专利,但同时也必须注意到其催化去除CO/NO的过程中存在的一些局限性:三效催化剂易中毒失效(三效催化剂的失活主要类型有:机械失活、热失活和化学失活);寿命短、工作温区窄;贵金属资源匮乏、成本高;贫燃条件下氮氧化物选择性低。
因此,如何提高低温去除CO/NO的反应活性、提高CO和NO的转化率和对N2的选择性对于汽车尾气净化有着重要的意义。
发明内容
本发明的目的在于克服单纯热催化去除CO/NO的不足,提高催化剂的低温活性及对N2的选择性,提供了一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂及其制备方法和应用,其通过将Pd负载在氮掺杂的二氧化钛上,以利用光热耦合作用提高Pd催化剂催化去除CO/NO的性能,解决了常规Pd催化剂及单纯的载体需在较高温度下才能催化CO/NO反应及N2选择性低的问题,且该催化剂制备方法简单易行,有利于推广应用。
为实现上述目的,本发明采用如下技术方案:
一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂,其是以N-TiO2为载体,Pd纳米粒子为活性组分构成的高分散负载型三效低温催化剂;其中,活性组分Pd的含量为0.5~2.5wt%。
如上所述负载型Pd催化剂在可见光照条件下,能够在60-100℃的低温下实现汽车尾气中CO及NO的去除,且在60℃时便达到催化剂的起燃温度。
如上所述负载型Pd催化剂的制备方法,采用氨水作为氮源再通过焙烧实现对TiO2掺氮;再利用沉积沉淀法在所得N-TiO2载体上负载活性组分Pd,其包括以下步骤:
(1)在冰水浴中,向100ml的氨水溶液中快速加入25ml的钛酸异丙酯作为前驱体,快速搅拌4~8h、水洗、在烘箱中80℃干燥、然后450℃煅烧半小时制得淡黄色的N-TiO2载体;
(2)在所得N-TiO2载体中加入1.2 mg/mL PdCl2溶液及去离子水,其PdCl2溶液的加入量为每1.2g的N-TiO2载体中加入5-25 mL;搅拌3h,随后加入过量含NaOH的NaBH4溶液,室温下搅拌5-8 h,离心,去离子水洗涤,80℃烘箱干燥,制得所述负载型Pd催化剂。
所述含NaOH的NaBH4溶液中,NaBH4的浓度为0.01-0.1mol/L,NaOH的浓度为0.01-0.1mol/L。
所得Pd/N-TiO2催化剂在低温以及可见光催化下,有可能实现汽车尾气及燃料排气的NO+CO的光热耦合转化,且以无毒绿色的N-TiO2为半导体的催化剂有望制备成涂抹型,其制备方法简单方便可行,更有利于推广应用。
值得注意的是,本发明催化剂并不是传统的光催化剂,其需要在一定温度下有热催化作用的基础上、引入可见光照才能显著促进催化活性(即呈现良好的光热耦合效应)。
本发明的显著优点在于:
(1)本发明以通过N掺杂后的TiO2得到的无毒绿色的N-TiO2为半导体作为载体,可以发现N掺杂后的TiO2对光响应由紫外到可见光,这便使得半导体在一定波长的可见光照下能够激发产生电子-空穴对,且富电子N的掺杂成功的引入了大量的氧空位以及Ti3+生成,当Pd负载于此类载体上,光生电子会从费米能级高的半导体转移至费米能级低的Pd金属上,从而提高活性金属Pd的表面电子密度,更有利于CO及NO的吸附和活化,进而促进CO/NO反应的进行,使CO、NO转化率和N2选择性得以提高;
(2)与单纯热催化反应相比,本发明通过选择具有光激发活性的半导体作为载体来制备Pd负载型催化剂,并根据NO+CO的反应特点,利用光热耦合作用显著提高催化剂催化去除CO/NO的性能,有效降低了反应温度,减少了能耗;
(3)本发明制备方法及应用操作简单易行,适于推广应用。
附图说明
图1为实施Pd/N-TiO2的扫描电镜图。
图2为实施Pd/N-TiO2的XRD图。
图3为实施Pd/N-TiO2的紫外-可见漫反射光谱图。
具体实施方式
为了使本发明所述的内容更加便于理解,下面结合具体实施方式对本发明所述的技术方案做进一步的说明,但是本发明不仅限于此。
实施例1
1 wt% Pd/N-TiO2催化剂的制备,具体步骤为:
1)在冰水浴中,向100ml的氨水溶液中快速加入25ml的钛酸异丙酯作为前驱体,快速搅拌6h、水洗、在烘箱中80℃干燥、然后煅烧制得淡黄色的N-TiO2载体;
2)在所得1.2g N-TiO2载体中加入10mL浓度为1.2 mg/mL PdCl2溶液及100mL的去离子水,搅拌3h,调节溶液的pH值至10左右,然后缓慢滴加浓度均为0.1mol/L的NaBH4和NaOH的混合溶液至过量,使Pd完全被还原,室温下搅拌6h,离心,去离子水水洗至离子浓度低于10ppm,80℃烘箱干燥,制得所述负载型Pd/N-TiO2催化剂。
图1为所得Pd/N-TiO2催化剂的扫描电镜图。从图1可以看出,Pd/N-TiO2催化剂呈现蜂窝煤且表面粗糙的小颗粒形貌,这种结果可能有助于反应物的传质,对于NO和CO的吸附有一定的促进作用。
图2为所得Pd/N-TiO2催化剂的XRD图。从图2中可以看出,由于Pd负载量与N掺杂的含量低,使得催化剂的XRD谱图中只出现了锐钛矿TiO2衍射锋,这也说明了催化剂中Pd粒子的均匀分散以及N的掺杂并没有影响TiO2的晶型结构。
图3为所得Pd/N-TiO2催化剂的紫外-可见漫反射光谱图。从图3中可以看出,催化剂载体N-TiO2在可见光区有很好的光吸收,且在负载贵金属Pd后,该催化剂对可见光的吸收增强,说明负载后的催化剂能更好地利用可见光,发挥其光促作用。
催化剂的性能评价
所得催化剂催化去除CO/NO的性能评价在一常压连续流动反应装置上进行。在带有进气口与出气口玻璃反应器(长30mm×宽15mm×高1mm)中,装填催化剂,通过由程序升温控温仪控制的加热装置给反应器提供所需温度,及用于激发半导体的滤光片(450 nm-760nm)和氙灯装置,所述氙灯装置发出的光能够透过石英玻璃反应器到达催化剂表面。
反应条件:将0.4g催化剂装填在玻璃反应器中,催化剂粒径约为0.2~0.3mm(60~80目)。反应气中CO和NO的含量分别固定为0.15V%及0.15V%,N2作为平衡补充气,反应气总流速约100mL/min。可见光源采用10W的LED灯带(10个1W的小灯泡串在一起、发光主波长为450-550nm),照在催化剂表面的光强度为182 mW/cm2。出气口气体采用AIDE-OW/AI300在线分析气氛中CO、NO、CO2的浓度,取反应2小时的结果计算CO转化率及N2的选择性。
CO转化率的计算公式为:C1=(VinCO-VoutCO)/VinCO×100%;
NO转化率的计算公式为:C2=(VinNO-VoutNO)/VinNO×100%;
N2选择性的计算公式为:S=2VoutN2/(VinNO-VoutNO)×100%。
式中,C1为CO的转化率,C2为NO的转化率,S为N2的选择性;VinCO和VoutCO分别为进气和出气中的CO含量(V%),VinNO和VoutNO分别为进气和出气中的NO含量(V%),VoutN2为流出气中的N2含量(V%)。
按照此方法,评价了实施 Pd/N-TiO2催化剂在不同条件下催化去除CO/NO的性能及对N2的选择性,其结果如表1所示.
表1 光照前后Pd含量1wt%的Pd/N-TiO2催化去除CO/NO的性能及对N2的选择性
表1结果显示,相比于纯热的反应条件,在同等条件下引入可见光后,CO、NO的转化率、N2的选择性都有很大的提高,证明该催化剂具有十分明显的光促效果;且其于100℃下即可达到100%的CO/NO转化率及N2选择性,证明该催化剂可实现有效低温催化,且0℃下并没有热催化效果,在此基础之上加入可见光照,同样没有催化效果,证明了该催化剂需要在一定热激发的基础下,引入可见光才显示催化活性,即此催化剂样品并不是传统的光催化剂。
实施例2
0.5 wt% Pd/N-TiO2催化剂的制备,具体步骤为:
1)在冰水浴中,向100ml的氨水溶液中快速加入25ml的钛酸异丙酯作为前驱体,快速搅拌6h、水洗、在烘箱中80℃干燥、然后煅烧制得淡黄色的N-TiO2载体;
2)在所得1.2g N-TiO2载体中加入5mL浓度为1.2 mg/mL PdCl2溶液及100mL的去离子水,搅拌3h,调节溶液的pH值至10左右,然后缓慢滴加浓度均为0.1mol/L的NaBH4和NaOH的混合溶液至过量,使Pd完全被还原,室温下搅拌6h,离心,去离子水水洗至离子浓度低于10ppm,80℃烘箱干燥,制得所述负载型Pd/N-TiO2催化剂。
实施例3
2.5 wt% Pd/N-TiO2催化剂的制备,具体步骤为:
1)在冰水浴中,向100ml的氨水溶液中快速加入25ml的钛酸异丙酯作为前驱体,快速搅拌6h、水洗、在烘箱中80℃干燥、然后煅烧制得淡黄色的N-TiO2载体;
2)在所得1.2g N-TiO2载体中加入25mL浓度为1.2 mg/mL PdCl2溶液及100mL的去离子水,搅拌3h,调节溶液的pH值至10左右,然后缓慢滴加浓度均为0.1mol/L的NaBH4和NaOH的混合溶液至过量,使Pd完全被还原,室温下搅拌6h,离心,去离子水水洗至离子浓度低于10ppm,80℃烘箱干燥,制得所述负载型Pd/N-TiO2催化剂。
以上所述仅为本发明的较佳实施例,凡依本发明申请专利范围所做的均等变化与修饰,皆应属本发明的涵盖范围。
Claims (5)
1.一种以氮掺杂二氧化钛为载体的Pd三效低温催化剂在可见光照条件下、60-100℃高效催化去除汽车尾气中CO及NO中的应用,其特征在于:所述催化剂是以N-TiO2为载体,Pd纳米粒子为活性组分构成的高分散负载型三效低温催化剂;其中,Pd纳米粒子在催化剂中的含量为0.5~2.5wt%。
2.根据权利要求1所述的应用,其特征在于:所述以氮掺杂二氧化钛为载体的Pd三效低温催化剂的制备方法:采用氨水作为氮源再通过焙烧实现对TiO2掺氮;再利用沉积沉淀法在所得N-TiO2载体上负载活性组分Pd。
3.根据权利要求2所述的应用,其特征在于:所述以氮掺杂二氧化钛为载体的Pd三效低温催化剂的制备方法包括以下步骤:
(1)在冰水浴中,向氨水溶液中快速加入钛酸异丙酯作为前驱体,快速搅拌、水洗、干燥、煅烧制得N-TiO2载体;
(2)在所得N-TiO2载体中加入PdCl2溶液及去离子水,搅拌3h,随后加入过量含NaOH的NaBH4溶液,室温下搅拌5-8 h,离心,去离子水洗涤,80℃烘箱干燥,制得以氮掺杂二氧化钛为载体的Pd三效低温催化剂。
4.根据权利要求3所述的应用,其特征在于:步骤(1)中氨水的用量为100ml,钛酸异丙酯的用量为25ml。
5.根据权利要求3所述的应用,其特征在于:步骤(2)中所述PdCl2溶液的浓度为1.2 mg/mL,其加入量为每1.2g N-TiO2载体中加入5-25 mL;所述含NaOH的NaBH4溶液中,NaBH4的浓度为0.01-0.1mol/L,NaOH的浓度为0.01-0.1mol/L。
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