介孔碳限域纳米Au催化剂的尺寸控制及用于选择氧化和还原
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- 英文论文题名：Size-control of confined gold nanoparticles in ordered mesoporous carbon and their applications in selective oxidation and reduction
- 论文作者：万颖 ; 付海滨
- 英文论文作者：Ying Wan ; Haibin Fu ; Department of Chemistry ; Shanghai Normal University
- 年：2016
- 作者机构：上海师范大学;
- 论文关键词：金纳米粒子 ; 无配体 ; 尺寸控制 ; 介孔碳 ; 选择性
- 会议召开时间：2016-07-01
- 会议录名称：中国化学会第30届学术年会摘要集-第三十二分会： 多孔功能材料
- 语种：中文
- 分类号：O643.36
- 学会代码：ZGHY
- 会议名称：中国化学会第30届学术年会-第三十二分会 ; 多孔功能材料
- 会议地点：中国辽宁大连
- 主办单位：中国化学会
- 学会名称：中国化学会
- 页数：1
- 文件大小：188k
- 原文格式：D
- 会议级别：全国
摘要
多孔碳载体与Au相互作用弱,传统的浸渍和沉积-沉淀等技术很难应用在碳载体上,但同时正是由于其弱相互作用,可用于研究Au纳米催化剂的活性中心。我们的研究思路是从介孔材料的结构着手,设计"镶嵌"在碳骨架中的纳米Au颗粒。在合成中,采用配位作用辅助表面活性剂自组装技术,引入含巯基配体,获得了负载在介孔碳载体上且金纳米颗粒周围没有任何保护剂的金纳米催化剂(尺寸为2.4-18 nm)。即使经过600°C高温处理,Au纳米颗粒也不易聚集或流失。将介孔碳限域纳米Au催化剂用于水相中苯甲醇选择氧化反应中。以9 nm Au为催化剂,在空气为氧化剂,常压及60°C条件下,TOF值可达2506 h~(-1~[1])。但此催化剂在低温条件下反应活性低。当Au纳米颗粒尺寸降低为3.4 nm时,在0°C反应条件下,TOF值可达31.2 h~(-1),远高于9 nm金催化剂。这可能是由于随着Au纳米颗粒粒径的减小,调变d-band电子性质,改善了低温下双氧物种在表面金原子的吸附性能,提高了3.4 nm金催化剂在低温下的催化氧化性能~~[2]。进一步的研究发现了在炭化过程中,由于C原子迁移进入Au纳米颗粒次表层,形成团簇;以及CO吸附可能导致Au表面原子重排,产生大量低配位Au物种。这一现象在小尺寸Au催化剂上尤为突出。因此,在尺寸为2.4 nm Au催化剂上,H_2解离能下降,芳硝基化合物被高效催化还原为相应胺化合物,对硝基苯酚和对氯硝基苯选择加氢反应TOF值可分别达14.2 min~(-1)和27.8 min~(-1)。
To take advantage of the particle size effect while minimizing the interface interaction effect for gold nanoparticles,a less-interacting support such as activated carbon is required.However current research related to gold on activated carbon severely lags that related to gold on oxides,possibly because of gold's redox properties and the ease of reducing Au(Ⅲ) precursors,resulting in the formation of large metallic aggregates.Monodispersed gold nanoparticles with a size of between 2.4 and 18 nm were immobilized on ordered mesoporous carbon in the absence of any protecting agent.This catalyst exhibits a high activity toward the selective oxidation of benzyl alcohol to benzyl acid and toward the reduction of p-nitrophenol to p-aminophenol at low temperatures such as0 ℃.A size-dependent selective oxidation over gold nanoparticles by the exposed surface atoms was observed at0 ℃,whereas the intrinsic activity at 25 ℃ was independent of size.The electronic modification of the d-orbitals of small particles is extremely important for chemisorption at low temperatures.
To take advantage of the particle size effect while minimizing the interface interaction effect for gold nanoparticles,a less-interacting support such as activated carbon is required.However current research related to gold on activated carbon severely lags that related to gold on oxides,possibly because of gold's redox properties and the ease of reducing Au(Ⅲ) precursors,resulting in the formation of large metallic aggregates.Monodispersed gold nanoparticles with a size of between 2.4 and 18 nm were immobilized on ordered mesoporous carbon in the absence of any protecting agent.This catalyst exhibits a high activity toward the selective oxidation of benzyl alcohol to benzyl acid and toward the reduction of p-nitrophenol to p-aminophenol at low temperatures such as0 ℃.A size-dependent selective oxidation over gold nanoparticles by the exposed surface atoms was observed at0 ℃,whereas the intrinsic activity at 25 ℃ was independent of size.The electronic modification of the d-orbitals of small particles is extremely important for chemisorption at low temperatures.
引文
[1]Wang,S.;Zhao,Q.F.;Wang,J.Q.;Cho,M.Terasaki,O.;Wan,Y.J.Am.Chem.Soc.2013,135:11849.
[2]Wang,S.;Wang,J.;Zhao,Q.F.;Li,D.D.;Wan,Y.ACS Catal.2015,5:797.
[2]Wang,S.;Wang,J.;Zhao,Q.F.;Li,D.D.;Wan,Y.ACS Catal.2015,5:797.