The significance of the oxidation state of gold in heterogeneous catalysis

我们的目标是构建一个详细的图片的过程中，中间体和活性位点参与乙炔氢氯化金纳米粒子支持在碳表面上。乙炔的氢氯化提供了氯乙烯的替代路线，氯乙烯目前是通过两步法生产的，包括乙烯的氧氯化形成1，2-二氯乙烷，然后裂解。氯乙烯聚合成聚氯乙烯（PVC），这是一种重要的聚合物，广泛应用于建筑和电子工业。60年前，氯乙烯几乎完全是由乙炔直接氢氯化制成的，乙炔来自煤，在氯化汞催化剂上，但从石油中获得廉价的乙烯导致了生产路线的改变，尽管产量较低，产品纯度较低，废物处理成本较高。现在，石油储量的减少和环保意识的提高要求人们寻找氧氯化路线的替代品。HgCl 2带来的安全和环境问题阻止了以前的催化剂的回归，但Hutchings和同事已经证明，碳载金是一种可行的替代品。我们的项目将告知这种催化剂的发展，但也将提供一个重要的新窗口，金催化。虽然金纳米粒子的催化是一个既定的现象，特别是在选择性氧化过程中，活性位点和反应机理的关键点仍然非常有争议，尽管广泛的工作。不同的研究人员分别强调了金催化剂不同方面的重要性，例如：金颗粒的大小;金与载体之间的界面以及金的氧化态。Fierro-Gonzalez和Gates将这一争议归因于注意力主要集中在CO氧化的机理研究上，并认为这种实验上吸引人的反应并不像它看起来那样简单。他们建议，如果要在了解金催化活性位点的性质方面取得进一步的进展，就必须在基础水平上研究更多样化的体系，从而为开发更好的金催化剂提供方向。Au/C催化剂受到表面科学界的关注非常少（与金/氧化物催化剂相反），因此，对该系统基础化学的研究不仅提供了推动重要的未来催化剂开发的前景，而且还提供了对金催化的一些基本原理的新认识。一个强大的组合的表面光谱，表面显微镜和表面动力学方法与计算化学结合应用将集中在识别和表征金的活性状态的理想模型的氢氯化催化剂。然而，在实践中，Au/C氢氯化催化剂由在表面上表现出多种官能团的高面积活性炭组成，所述官能团可影响吸附的卤化金的沉积和稳定性。为了解决这个问题，该项目涉及三个独立的平行链，研究在环境条件下从水溶液中沉积在改性HOPG和活性炭上的金，为HOPG上卤化金的模型表面科学/计算研究和实际催化之间提供桥梁。

We aim to construct a detailed picture of the processes, intermediates and active sites involved in the hydrochlorination of ethyne over gold chloride nanoparticles supported on carbon surfaces. The hydrochlorination of ethyne provides an alternative route to vinyl chloride which at present is manufactured by a two step process involving the oxychlorination of ethene to form 1,2-dichloroethane followed by cracking. Vinyl chloride is polymerised to polyvinyl chloride (PVC) an important polymer with widespread applications in the construction and electronics industries. Sixty years ago vinyl chloride was almost exclusively made by the direct hydrochlorination of ethyne, which derives from coal, over a mercury chloride catalyst but the availability of inexpensive ethene from oil led to a change of manufacturing route despite the lower yields, lower product purity and higher costs for waste treatment. Now, dwindling oil reserves and increasing environmental awareness is dictating a search for to the alternatives to the oxychlorination route. The safety and environmental issues posed by HgCl2 prevent a return to the former catalyst but Hutchings and co-workers have proven that gold supported on carbon can be a viable alternative. Our project will inform the development of such catalysts but will also provide an important new window on gold catalysis.Whilst catalysis by gold nanoparticles is an established phenomenon particularly in relation to selective oxidation processes, the key points of the active site and the reaction mechanism remain very controversial despite extensive work. Different researchers have separately emphasised the importance of different aspects of gold catalysts for example: the size of the gold particles; the interface between the gold and the support and the oxidation state of the gold. Fierro-Gonzalez & Gates ascribe this controversy to the fact that attention has largely focussed on mechanistic studies of CO oxidation and suggest that this experimentally appealing reaction is not as straight forward as it appears. They recommend that more diverse systems be investigated at a fundamental level if further progress is to be made in understanding the nature of the active site in gold catalysis and thus provide direction to the development of better gold catalysts. Au/C catalysts have received remarkably little attention from the surface science community (in contrast to the gold/oxide catalysts) and a study of the fundamental chemistry underlying this system therefore offers the prospect not only of advancing the development of an important future catalyst but also of shedding new light on some of the fundamental principles of gold catalysis. A powerful combination of surface spectroscopy, surface microscopy and surface kinetic methods applied in conjunction with computational chemistry will be focussed on identifying and characterising the active states of gold in ideal models of the hydrochlorination catalyst. However, in practice, the Au/C hydrochlorination catalyst consists of a high area activated carbon exhibiting a variety of functional groups at the surface which may influence the deposition and stability of the adsorbed gold halides. To address this issue the project involves three separate parallel strands with studies of gold deposited from aqueous solutions on modified HOPG and activated carbon under ambient conditions providing the bridge between model surface science/computational studies of gold halides on HOPG and the practical catalysis.