Nitridic and Carbidic Interstitial Pd Nanoparticles for Directed Catalysis

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).