CN107519871B - 一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法 - Google Patents
一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法 Download PDFInfo
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Abstract
本发明属于CO低温催化氧化催化剂的技术领域,具体涉及一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法。本发明结合合金粒子和核壳结构两方面的优点,提供了一种制备步骤简单,催化活性和稳定性优异的合金类AuAg@SiO2纳米催化剂的制备方法,本发明的制备方法得到催化剂,其内核为AuAg合金粒子,外壳为SiO2,AuAg的粒径为2‑5 nm,该核壳结构催化剂的直径在50‑120 nm之间,内核AuAg合金粒子中不同金属成分间的协同作用大幅提升了催化剂对CO低温氧化的活性,外壳SiO2有效防止合金粒子的迁移聚集,提高了催化剂的稳定性。该新型结构催化剂呈现出优异的CO低温催化氧化活性和稳定性。
Description
技术领域
本发明属于CO低温催化氧化催化剂的技术领域,具体涉及一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法。
背景技术
随着工业发展和城市人口集中,人类在生产和生活中向环境排放的污染物日趋增多,各类污染物已经严重威胁到人类及其它生物的生存和发展,改善生存环境、提高环境质量已成为全球可持续发展战略的重要内容。其中,由于化石燃料的不完全燃烧和汽车尾气的排放,CO气体已成为许多工业作业和室内环境的首要污染物,在火灾现场、矿井坑道、城市路口、用煤或煤气取暖的室内均可能大量存在。去除CO或降低环境中CO浓度至安全范围对维护人体健康、改善生存环境非常必要。在去除CO的各类方法中,环境温度下使用多相催化剂将CO氧化成CO2是最直接、简单易行的有效途径。因此,开发具有优异CO催化氧化性能的催化剂成为当前亟待解决的问题之一。
自Haruta发现负载型的贵金属Au催化剂对CO氧化呈现出较好的低温催化活性后,金基纳米催化剂就成为催化氧化CO的研究热点[M. Haruta, T. Kobayashi, H. Sano, N.Yamada, Novel gold catalysts for the oxidation of carbon monoxide at atemperature far below 0℃, Chem. Lett., 1987, 16, 405-406]。但Au纳米颗粒的催化活性依赖于粒子尺寸,粒径<3nm的Au颗粒催化活性较高,[T. Zhang, H. Zhao, S. He, K.Liu, H. Liu, Y. Yin, and C. Gao, Unconventional Route to EncapsulatedUltrasmall Gold Nanoparticles for High-Temperature Catalysis, ACS nano, 2014,8, 7297-7304]但尺寸较小的金纳米颗粒稳定性差,在催化反应过程中易迁移聚集使催化活性大幅下降。因此,设计并制备复合型纳米催化剂以满足实际应用对催化剂性能的要求十分必要。
以多组分合金代替单一组分的金属,可使合金粒子之间各组分产生协同效应能够在一定程度上打破尺寸效应。且以比金价格低廉的金属取代部分的金可降低催化剂成本和贵金属消耗,为该类催化剂实际应用提供有利条件。Mou等人发现,尺寸为30nm的AuAg合金呈现出比粒径为6.7nm的Au颗粒更优异的CO催化活性。[X. Liu, A. Wang, X. Yang, T.Zhang, C. Y. Mou, Synthesis of thermally stable and highly active bimetallicAu-Ag nanoparticles on inert supports, Chem. Mater., 2009, 21, 410-418.] Chen等人发现将AuAg合金粒子负载型催化剂Au-Ag/CeO2在180℃煅烧后没有团聚,但升高煅烧温度至350℃后Au-Ag合金颗粒发生明显团聚,催化活性大大降低[N. Sasirekha, P.Sangeetha, and Y.-W. Chen, Bimetallic Au-Ag/CeO2 catalysts for preferentialoxidation of CO in hydrogen-rich stream: effect of calcination temperature,J. Phys. Chem. C, 2014, 118, 15226-15233.]由上可以看出,虽然合金粒子能够提高催化剂活性,但常见的负载型合金粒子催化剂稳定性较差,高温下易团聚失活。
核壳结构催化剂以具有高催化活性的金属粒子为核,氧化物为壳。此类结构既能避免金纳米颗粒在催化过程中聚集流失,又能增加内核金属粒子和外壳氧化物的作用面积,从而促进异质界面处协同效应发生,提高催化剂活性。Liu 等人制备了Au-HKUST-1 纳米胶囊结构的催化剂,该催化剂对CO 氧化反应表现出优异的稳定性和重复利用性。但是由于所制备的Au粒径较大,该催化剂在180℃下才使CO完全转化。 [Y. Liu, J. Zhang, L.Song, W. Xu, Z. Guo, Au-HKUST-1 Composite Nanocapsules: Synthesis with aCoordination Replication Strategy and Catalysis on CO Oxidation, ACS Appl.Mater. Interfaces, 2016, 8, 22745-22750]。
由上述可知,合金类催化剂虽能一定程度上增强催化剂活性但稳定性不足。核壳结构催化剂的制备步骤较为繁琐,且内核多为单一组分的纳米粒子,其催化活性受尺寸效应影响较大。
发明内容
为了解决金纳米催化剂易团聚失活且催化活性严重依赖于粒径尺寸的问题,本发明结合合金粒子和核壳结构两方面的优点,提供了一种制备步骤简单,催化活性和稳定性优异的合金类AuAg@SiO2纳米催化剂的制备方法。
为实现上述目的,本发明采用如下技术方案:
一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法,具体步骤如下:
(1)将10mM HAuCl4溶液和10mM AgNO3溶液混合,加入0.1g/ml的表面活性剂溶液,室温下搅拌20-30min,加入0.1M硼氢化钠溶液,搅拌3h,得AuAg合金溶胶;所述10mM HAuCl4溶液、10mM AgNO3溶液、0.1g/ml表面活性剂和0.1M硼氢化钠的体积比为1:0.25-4:0.5-10:1-10;
(2)取步骤(1)所得AuAg合金溶胶加入溶剂,搅拌下加入正硅酸四乙酯(TEOS),混合均匀后滴加28%w.t氨水,继续搅拌,搅拌时间为2-5小时;其中溶剂为水和醇的混合液,水和醇的体积比为1:1.25-5;AuAg合金溶胶、正硅酸四乙酯和28%w.t氨水的体积比为1:0.05-0.3:0.1-1。
(3)将步骤(2)所得产品以8000 rpm/min离心5分钟后收集沉淀,采用溶剂洗涤后干燥。
所述步骤(1)中,表面活性剂选自聚乙烯吡咯烷酮(PVP),聚乙烯醇(PVA)和十二烷基三甲基溴化铵(TTAB)中的至少一种;所述表面活性剂溶液采用水进行溶解。
所述步骤(2)中,醇选自甲醇、乙醇和异丙醇中的一种。
所述步骤(2)中,所述氨水的滴加速度为50-150μL/min。
所述步骤(3)中溶剂选自乙醇、甲醇、异丙醇和水中的至少一种;干燥温度60-80℃。
本发明创新地以合金粒子作为核壳结构中的内核,提高了催化剂低温催化活性,一定程度上打破尺寸效应;以SiO2为外壳,提高了催化剂的稳定性。上述方法所制备的AuAg@SiO2核壳结构纳米催化剂,内核为AuAg合金粒子,粒径为2-5nm,外壳为SiO2,直径为50-120nm。
本发明的有益效果如下:
本发明的制备方法得到的催化剂其内核为AuAg合金粒子,外壳为SiO2,AuAg合金的粒径为2-5nm,该核壳结构催化剂的直径在50-120nm之间。本发明制备过程简单、反应条件温和,改变条件可以调控核壳结构的尺寸,及SiO2球中AuAg合金粒子的个数。本发明所制备催化剂中AuAg合金粒子不同金属成分间的协同作用使催化剂在40-90℃下对CO氧化反应具有很好的催化活性,在75℃下即可实现CO完全转化。SiO2外壳有效防止内核金属粒子的团聚,大大提高了催化剂的稳定性,催化剂在80℃下长时间保持高活性,对低温下CO的催化氧化反应具有活性高和稳定性好的特点。
附图说明
图1为实施例1制备的AuAg@SiO2核壳结构纳米催化剂透射电镜图;
图2为实施例2制备的AuAg@SiO2核壳结构纳米催化剂透射电镜图;
图3为实施例3制备的AuAg@SiO2核壳结构纳米催化剂透射电镜图
图4为实施例4制备的AuAg@SiO2核壳结构纳米催化剂透射电镜图;
图5为实施例5制备的AuAg@SiO2核壳结构纳米催化剂透射电镜图;
图6为对比例制备的AuAg/SiO2负载型纳米催化剂透射电镜图;
图7为多种催化剂对CO氧化反应的催化活性测试;
图8为多种催化剂在80℃下稳定性测试。
具体实施方式
下面结合附图对本发明的技术方案进行详细的说明,但本发明不受下述实施例的限制。
实施例1
(1)向5ml的圆底烧瓶中加入400μL浓度为10mM的HAuCl4和100μL浓度为10mM的AgNO3溶液分散至20ml水中,加入2mL浓度为0.1g/ml的PVP溶液,室温下搅拌30min后,一次性加入2ml新配制浓度为0.1mol/L的NaBH4溶液,搅拌3h后得到AuAg合金的溶胶。
(2)取4ml H2O同20ml乙醇混合后加入3ml AuAg溶胶溶液,随后加入正硅酸四乙酯(TEOS)300μL,搅拌均匀后逐滴加入28%氨水溶液800μL,氨水的滴加速度为80μL/min。
(3)室温搅拌5h后,离心收集产物,用乙醇洗涤3次后,于80℃下干燥过夜。
所制备的AuAg@SiO2核壳结构纳米催化剂的透射电镜图片如图1所示。内核AuAg合金粒子粒径为4 nm,外壳二氧化硅球的直径约为50 nm,每个SiO2球体中包覆1个AuAg合金粒子。
实施例2
(1)向50 ml的圆底烧瓶中加入300μL浓度为10mM的HAuCl4和200μL浓度为10mM的AgNO3溶液分散至20ml水中,加入0.2mL浓度为0.1g/ml的PVA溶液,室温下搅拌30min后,一次性加入2ml新配制浓度为0.1mol/L的NaBH4溶液,搅拌4h后得到AuAg合金的溶胶。
(2)同实施例1。
(3)同实施例1。
所制备的AuAg@SiO2核壳结构纳米催化剂的透射电镜图片如图2所示。内核AuAg合金粒子粒径约为4nm,外壳二氧化硅球的直径约为50nm,每个SiO2球体中包覆1个AuAg合金粒子。
实施例3
(1)向50 ml的圆底烧瓶中加入300μL浓度为10mM的HAuCl4和200μL浓度为10mM的AgNO3溶液分散至20ml水中,加入0.2mL浓度为0.1g/ml的PVA溶液,室温下搅拌30min后,一次性加入2ml新配制浓度为0.1mol/L的NaBH4溶液,搅拌3h后得到AuAg合金的溶胶。
(2)取5ml H2O同20ml乙醇混合后加入2ml AuAg溶胶溶液,随后加入正硅酸四乙酯(TEOS)300μL,搅拌均匀后逐滴加入28%氨水溶液800μL,氨水的滴加速度为80μL/min。
(3)同实施例1。
所制备的AuAg@SiO2核壳结构纳米催化剂的TEM图如图3所示,内核AuAg合金粒子粒径为4nm,外壳二氧化硅球的直径约为50nm,大多数SiO2球体中包覆1个AuAg合金粒子,个别球中没有合金粒子。
实施例4
(1)向50 ml的圆底烧瓶中加入300μL浓度为10mM的HAuCl4和200 μL浓度为10 mM的AgNO3溶液分散至20ml水中,加入2mL浓度为0.1g/ml的PVP溶液,室温下搅拌30min后,一次性加入2ml新配制浓度为0.1mol/L的NaBH4溶液,搅拌3h后得到AuAg合金的溶胶。
(2)取1ml H2O同20ml乙醇混合后加入6ml AuAg溶胶溶液,随后加入正硅酸四乙酯(TEOS)300μL,搅拌均匀后逐滴加入28%氨水溶液800μL,氨水的滴加速度为80μL/min。
(3)同实施例1。
所制备的AuAg@SiO2核壳结构纳米催化剂的TEM图如图4所示,内核AuAg合金粒子粒径为4nm,外壳二氧化硅球的直径约为50nm,多数SiO2球体中包覆多个AuAg合金粒子。
实施例5
(1)同实施例1。
向50 ml的圆底烧瓶中加入400μL浓度为10mM的HAuCl4和100μL浓度为10mM的AgNO3溶液分散至20ml水中,加入2mL浓度为0.1g/ml的PVP溶液,室温下搅拌30min后,一次性加入1ml新配制浓度为0.1mol/L的NaBH4溶液,搅拌3h后得到AuAg合金的溶胶。
(2)取4ml H2O同20ml乙醇混合后加入3ml AuAg溶胶溶液,随后加入正硅酸四乙酯(TEOS)700μL,搅拌均匀后逐滴加入28%氨水溶液2mL,氨水的滴加速度为80μL/min。
(3)室温搅拌5h后,离心收集产物,用异丙醇洗涤3次后,于80℃下干燥过夜。
所制备的AuAg@SiO2核壳结构纳米催化剂的TEM图如图5所示,内核AuAg合金粒子粒径为4nm,外壳二氧化硅球的直径为100nm,大多数SiO2球体中包覆1个AuAg合金粒子。
对比例
(1)取7ml H2O同20ml乙醇混合后加入正硅酸四乙酯(TEOS)300μL,搅拌均匀后逐滴加入28%氨水溶液800μL,氨水的滴加速度为80μL/min。搅拌3h后离心用异丙醇洗涤,并超声分散于50ml异丙醇中。
(2)搅拌下向分散于异丙醇的SiO2逐滴加入150ul 3-氨丙基三乙氧基硅烷(APTES),加热回流12h后降温,离心用乙醇洗涤3次后分散于20ml水中。
(3)搅拌下向分散于水中的SiO2-APTES中加入400μL浓度为10mM的HAuCl4和100μL浓度为10mM的AgNO3溶液,再加入2mL浓度为0.1g/ml的PVP溶液,室温下搅拌30min后,一次性加入2 ml新配制浓度为0.1 mol/L的NaBH4溶液,搅拌3h后离心,乙醇洗涤后70℃干燥3h得到AuAg/SiO2负载型催化剂。
所制备的AuAg/SiO2核壳结构纳米催化剂的透射电镜图片如图6所示,载体二氧化硅球的直径为70nm,其表面负载有多个粒径约4nm 的AuAg合金粒子。
AuAg@SiO2核壳结构纳米催化剂的性能评价
分别取30 mg催化剂与300 mg的石英砂混合均匀后填充到石英管中。程序升温加热,床层温度以热电偶检测。反应气体组成为1% CO:10% O2:89% N2,以气相色谱仪在线监测气体成分变化。AuAg@SiO2核壳结构纳米催化剂对CO氧化活性如图7所示,实施例1,2,4所制备AuAg@SiO2核壳结构催化剂表现出优异的CO催化氧化活性,60℃时CO的转化率在70%-80%,在80℃左右可实现CO完全转化。这说明AuAg合金粒子中不同金属成分间协同作用提高催化剂性能,使其具有优异的低温催化活性。实施例3所制备的催化剂活性稍差,这可能同AuAg合金粒子的含量较少有关。实施例5所制备的催化剂活性进一步减弱,这说明AuAg@SiO2核壳结构中,SiO2外壳厚度对催化活性有影响,外壳过厚使催化活性降低。对比例中AuAg/SiO2负载型催化剂活性随温度的升高先升高后迅速降低,这是因为负载型催化剂中载体同金属粒子之间作用力较弱,随着温度的持续升高合金粒子迁移聚合使催化活性降低。
AuAg@SiO2核壳结构纳米催化剂的稳定性评价
分别取30mg催化剂与300mg的石英砂混合均匀后填充到石英管中。80℃下保温12h,床层温度以热电偶检测。反应气体组成为1% CO:10% O2:89% N2,以气相色谱仪在线监测气体成分变化。AuAg@SiO2核壳结构纳米催化剂对CO氧化活性如图8所示。在考察过程中,实施例中所制备的AuAg@SiO2核壳结构催化剂的活性基本保持不变,都呈现出优异的稳定性。催化剂良好的稳定性得益于SiO2外壳对内核AuAg合金粒子的保护作用,有效抑制了合金粒子的迁移长大。对比例中所制备的AuAg/SiO2负载型催化剂催化活性迅速降低逐渐趋于稳定,这一现象验证了负载型催化剂稳定性较差,再次说明核壳结构有利于提高催化剂稳定性。
Claims (3)
1.一种催化氧化CO的AuAg@SiO2纳米催化剂的制备方法,具体步骤如下:
(1)将10mM HAuCl4溶液和10mM AgNO3溶液混合,加入0.1g/ml的表面活性剂溶液,室温下搅拌20-30min,加入0.1M硼氢化钠溶液,搅拌3h,得AuAg合金溶胶;所述10mM HAuCl4溶液、10mM AgNO3溶液、0.1g/ml表面活性剂溶液和0.1M硼氢化钠溶液的体积比为1:0.25-4:0.5-10:1-10;
(2)取步骤(1)所得AuAg合金溶胶加入溶剂,搅拌下加入正硅酸四乙酯(TEOS),混合均匀后滴加28%w.t氨水,继续搅拌,搅拌时间为2-5小时;其中溶剂为水和乙醇的混合液,水和乙醇的体积比为1:1.25-5;AuAg合金溶胶、正硅酸四乙酯和28%w.t氨水的体积比为1:0.05-0.3:0.1-1;
(3)将步骤(2)所得产品以8000 r/min离心5分钟后收集沉淀,采用溶剂洗涤后干燥;
所述步骤(1)中,表面活性剂选自聚乙烯吡咯烷酮(PVP),聚乙烯醇(PVA)和十二烷基三甲基溴化铵(TTAB)中的至少一种;所述表面活性剂溶液采用水进行溶解;
步骤(2)中,所述氨水的滴加速度为50-150μL/min。
2.根据权利要求1所述的催化氧化CO的AuAg@SiO2纳米催化剂的制备方法,其特征在于,步骤(3)中溶剂选自乙醇、甲醇、异丙醇和水中的至少一种;干燥温度60-80℃。
3.根据权利要求1或2所述的催化氧化CO的AuAg@SiO2纳米催化剂的制备方法,其特征在于,制备得到的AuAg@SiO2核壳结构纳米催化剂,内核为AuAg合金粒子,粒径为2-5nm,外壳为SiO2,直径为50-120nm,每个独立的SiO2纳米球中只包覆1个小尺寸AuAg合金粒子。
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