Nitridic and Carbidic Interstitial Pd Nanoparticles for Directed Catalysis

在催化领域，负载型金属纳米颗粒是一类重要的材料；它们是一种既节省昂贵金属又改变催化性能的方便方法。然而，这些材料是非常动态的，对反应过程中经历的环境条件的波动特别敏感。这些结构转变不是良性的，它们支撑着这类催化剂的工作功能。在这项研究中，我们将利用我们在这一领域的专业知识，为环保和化工行业设计新的活性催化剂。在没有意识到这一点的情况下，大多数人每天都会使用或购买由负载型钯纳米颗粒催化剂制成的产品。这些类型的材料是汽车尾气催化转化器中的活性成分，并用于制造许多精细化学品。然而，它们的性能会受到与它们相互作用的反应物气体的影响，改变Pd NPs的结构，其中Pd原子会与H、N或C原子（取决于存在的气体）相互点缀。从它们在反应中的形成和稳定性方面了解这些新结构有助于理解它们对反应的影响。例如，我们最近报道了氮化物间质Pd NPs的形成（Nature Catalysis, 2,157, 2019），以及它在指导氨氧化成N2中的作用。这种反应对于柴油发动机来说尤为重要，因为柴油发动机中未使用的氨会“溜”出尾气，增加不必要的排放。我们发现，在氮化Pd存在的情况下，氨转化为N2，而在没有氮化相的情况下，氨过度氧化为污染物NOx。我们的愿景是预先形成间隙Pd纳米颗粒结构，并利用其独特的催化性能，即它们能够调节氧化和氢化化学-催化的基础-以限制过度氧化和过度还原产物。为了实现这一目标，该项目必须首先了解这些结构是如何形成的，以及在什么条件下它们保持稳定。这将通过开发元素特定光谱来实现，该光谱提供了工艺条件下Pd （XAFS）和杂原子环境（MAS NMR）的直接信息。这些结果将进一步支持DFT模拟研究的实际尺寸的纳米颗粒结构。最终，这将生成一个“规则手册”，说明这些结构是如何/何时形成的，以及它们在不同条件下（例如温度和气体环境）的稳定性。

In the field of catalysis, supported metal nanoparticles are an important class of materials; they are a convenient way to thrift expensive metals alongside altering the catalytic properties. However, these materials are extraordinarily dynamic and are particularly sensitive to the fluctuation of environmental conditions experienced during reactions. These structural transformations are not benign and they underpin the working function of this class of catalysts. In this study, we will use our expertise in this area to design new active catalysts for environmental protection and the chemicals industry.Without ever realising it, on a daily basis most people will be using or buying products made using supported Pd nanoparticle catalysts. These types of materials are an active component in catalytic converters in car exhausts, and used in the manufacture of many fine chemicals. However, their performance can be affected by the reactant gases they interact with, changing the structure of the Pd NPs, where the Pd atoms become interspersed with H, N or C atoms (depending on the gas present). Understanding these new structures, in terms of their formation and stability during reaction can help understand the influence they have on reactions. For example, we recently reported the formation of nitride interstitial Pd NPs (Nature Catalysis, 2, 157, 2019), and its role in directing the oxidation of ammonia to N2. This reaction is of particular importance for diesel engines where unused ammonia can 'slip' through the exhaust, adding to unwanted emissions. We found that in the presence of the Pd nitride, ammonia is converted to N2, whereas without the nitride phase, there is over oxidation to the pollutant NOx.Our vision is to pre-form interstitial Pd nanoparticle structures and exploit their unique catalytic properties, i.e. they are able to moderate oxidation and hydrogenation chemistry - fundamental to catalysis - to limit over-oxidation and over-reduction products. To achieve this the project must first learn more about how these structures are formed and under what conditions they remain stable. This will be realized by developing element specific spectroscopy that provides direct information on the Pd (XAFS) and the heteroatom environments (MAS NMR) under process conditions. These results will be further supported by DFT modelling studies of realistically sized nanoparticle structures. Ultimately, this will generate a 'rulebook' for how/when these structures are formed and their stability under different conditions (e.g. temperature gas environment).