稳定于具有亚5nm窗口的立方介孔氧化硅的金纳米颗粒及其优异的醇氧化活性（英文）

发布时间：2018-01-15 22:19

  本文关键词：稳定于具有亚5nm窗口的立方介孔氧化硅的金纳米颗粒及其优异的醇氧化活性（英文）　出处：《催化学报》2017年03期 　论文类型：期刊论文

  更多相关文章： 金纳米颗粒 立方介孔氧化硅 窗口尺寸 抗烧结性能 醇氧化

【摘要】：金纳米颗粒在烯烃加氢、水气转化、过氧化氢直接合成和醇类选择性氧化等反应中表现出独特的催化性能,引起了人们广泛关注.通常,金纳米颗粒的催化活性受到尺寸、原子堆积形式、暴露晶面及其与载体的相互作用所影响.而金纳米颗粒的烧结往往导致其催化效率迅速下降.为了解决金颗粒烧结问题,提高其使用寿命,必须控制高温处理时颗粒和原子的迁移.尽管已有很多工作见诸报道,然而到目前为止,仍未完全解决金颗粒烧结问题.本文通过调整有机模板剂和反应温度成功地合成了不同窗口尺寸的立方介孔氧化硅材料(FDU-12),并将预先合成的3nm金颗粒负载于其上,考察了窗口尺寸对金颗粒烧结的影响.首先,采用小角X射线散射、氮气吸附-脱附、透射电镜和扫描电镜等手段证实成功合成了具有亚5 nm窗口的FDU-12材料,同时以3 nm金颗粒为探针,进一步区分了具有3 nm和3 5nm窗口的FDU-12样品.在抗烧结实验中发现,具有3 5 nm窗口尺寸的FDU-12能够在一个较宽的金负载量(1.0 8.3 wt%)下稳定金纳米颗粒.在550 ℃空气中焙烧5 h后,金颗粒的平均尺寸维持在4.5 5.0 nm.更小的窗口尺寸则会导致3 nm金颗粒无法进入FDU-12孔道,从而带来低的负载能力和差的抗烧结性能.另一方面,具有7 nm窗口尺寸的FDU-12则只在高的金颗粒负载量(9 wt%)下才表现出较好的抗烧结性能,低负载量时烧结严重(2.1 wt%,14.2±5.5 nm).我们推测,合适的窗口尺寸(3 5 nm)恰好能允许3 nm金颗粒进入FDU-12的孔道,在高温处理过程中,当金颗粒长大到5nm左右时,窗口极大地限制了金颗粒的移动,导致其不能在孔与孔之间自由迁移.此外,该FDU-12材料的孔径为18 nm,这使得封装在各个孔内部的金颗粒与其他金颗粒距离较远,不利于其通过原子迁移而发生烧结.因此,拥有3 5 nm窗口尺寸的FDU-12在一个宽的金负载量下表现出良好的抗烧结能力.而对于具有7 nm窗口尺寸的FDU-12,在高的金负载量下,它可通过自聚焦效应抑制原子迁移,从而具有优良的抗烧结性能.但在低负载量时,介孔氧化硅的绝大部分孔内并不包含多个金颗粒,自聚焦效应无法发挥作用,在高温焙烧时金颗粒可以通过大的窗口尺寸相互融合导致烧结.我们将具有不同金尺寸的Au NP/FDU-12催化剂用于环己醇选择性氧化反应中.结果表明,4.5 nm的金催化剂表现出最好的活性(1544 mmol g_(Au)~(-1)h~(-1))和大于99%的选择性(230 ℃),大大超过了先前报道的基于Ag和Mn为活性中心的催化剂.另外,与负载在商用γ-Al_2O_3上相比,Au NP/FDU-12体系表现出了很好的选择性,直接脱水产物小于1%.同时可以保持100 h内金颗粒不发生烧结,活性不明显下降.
[Abstract]:Gold nanoparticles exhibit unique catalytic properties in olefin hydrogenation, water-gas conversion, direct synthesis of hydrogen peroxide and selective oxidation of alcohols. The catalytic activity of gold nanoparticles depends on the size, atomic stacking form. In order to solve the problem of sintering gold particles and improve their service life, the sintering of gold nanoparticles often leads to a rapid decline in catalytic efficiency. It is necessary to control the migration of particles and atoms during high temperature treatment. Although a lot of work has been reported, so far. The problem of gold particle sintering has not been completely solved. In this paper, cubic mesoporous silicon oxide materials with different window sizes have been successfully synthesized by adjusting the organic template and reaction temperature. The effect of window size on the sintering of gold particles was investigated by loading the pre-synthesized 3nm gold particles on it. Firstly, small angle X-ray scattering and nitrogen adsorption-desorption were used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that FDU-12 materials with sub-5 nm window were successfully synthesized, and 3nm gold particles were used as probes. The FDU-12 samples with 3 nm and 3 5 nm windows were further distinguished. The FDU-12 with a window size of 3 ~ 5 nm is capable of being measured at a wide gold load of 1. 0 ~ 8. 3 wts. The gold nanoparticles were calcined at 550 鈩，

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