Oxidation Catalysis by Gold Nano-Particles supported on h-BN Nanomesh

负载型金纳米颗粒在多种化学反应中具有优异的低温活性和选择性，是一种很有前途的氧化催化剂。然而，负载型纳米金催化剂在典型反应条件下的烧结存在较大问题。对于Au/TiO2（110）氧空位或氧化（碱性）TiO2(110)，可以为在500K下固定Au团簇提供成核位点。然而，对于Au粒子在TiO2（110）上的低温活性的微观过程，文献中仍有争议。最近在Rh（111）和Ru（0001）上发现的六方BN （h-BN）纳米网为支持金纳米颗粒提供了独特的坚固的无氧模板。h-BN/Ru（0001）纳米网由2nm宽的周期性六边形孔阵列组成，晶格常数为3.25 nm。h-BN纳米网可以看作是一个高度规则的捕获位点网络，其中沉积的Au原子优先凝结成Au纳米粒子。这使得制备有序的模型催化剂成为可能。利用Au/h-BN/Ru（0001）模型催化剂，我们将通过原位实验和从头计算来阐明Au颗粒的氧化行为及其在氧化反应中的催化行为，包括简单的CO氧化和丙烯环氧化的“梦想反应”。无氧的氢氮化硼纳米网载体显著地促进了用光谱方法鉴定金颗粒上的催化活性氧。本项目的主要目标是推进对不受支撑氧化物表面缺陷位置影响的负载金团簇的低温活性的分子理解。利用光电发射光谱研究了金和氧化金团簇的电子性质，并与第一性原理电子结构计算进行了比较。催化氧化反应将通过原位红外实验/在线质谱法进行研究，并通过ab-initio计算详细模拟。

Supported Au nano-particles are considered as promising oxidation catalysts with superior low temperature activity and selectivity in a variety of chemical reactions. However, supported nano Au-catalysts are facing a major problem with sintering under typical reaction conditions. For the case of Au/TiO2(110) oxygen vacancies or oxidized (alkaline) TiO2(110) may provide nucleation sites for immobilizing the Au clusters up to 500K. However, the microscopic processes responsible for the low temperature activity of Au particles on TiO2(110) are still controversially discussed in the literature. The recently discovered nanomesh of hexagonal BN (h-BN) on Rh(111) and on Ru(0001) offers a unique sturdy oxygen-free template for supporting Au nanoparticles. The h-BN/Ru(0001) nanomesh consists of a periodic hexagonal array of 2 nm wide pores with a lattice constant of 3.25 nm. The h-BN nanomesh can be viewed as a highly regular network of trapping sites in which deposited Au atoms preferentially condense into Au nano particles. This allows for the preparation of well-ordered model catalysts. With the Au/h-BN/Ru(0001) model catalyst we shall perform in-situ experiments and ab-initio calculations to elucidate both the oxidation behavior of Au particles and its catalytic behavior in oxidation reactions, including the simple CO oxidation and the “dream reaction” of propylene epoxidation. The oxygen-free h- BN nanomesh support facilitates significantly the identification of the catalytically active oxygen species on the Au particles with spectroscopic methods. The major goal of the present project is to advance the molecular understanding on the low-temperature activity of supported Au clusters which are not affected by defect sites of the supporting oxide surface. Electronic properties of the Au and oxidized Au clusters will be studied by photoemission spectroscopy and compared with first principles electronic structure calculations. The catalyzed oxidation reaction will be studied by in-situ infrared experiments/on-line mass spectrometry and modeled in detail by ab-initio calculations.