Darby, Matthew T.; (2018) Towards the Understanding and Development of Single Atom Alloy Catalysts from First Principles. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Many industrial heterogeneous catalysts often use precious metals such as Pt and Pd thanks to their ability to catalyse a vast array of chemical reactions with exceptional activity. Unfortunately, the excellent reactivity of these metals results in poor selectivity, high susceptibility to poisoning and catalyst deactivation. One strategy that has been fruitful in overcoming these shortcomings is to alloy the catalytically active metals with those that are more selective, for example the coinage metals. A special class of these bimetallic surfaces may be formed by doping the inert host metal with a sufficiently low concentration of the catalytically active metal such that these dopant atoms isolate as individual, atomic dispersed ensembles in the surface layer of the host metal; such a material is known as a Single Atom Alloy (SAA). In this thesis, we use a dual-scale theoretical approach to develop a fundamental understanding of SAAs and their behaviour in catalytic systems. On the atomistic level, we make use of density functional theory (DFT) to investigate the electronic structure of SAAs, evaluating their thermodynamic stability and quantifying their surface interactions with various chemical species. Combining data acquired from DFT with kinetic Monte Carlo (KMC) simulation, we perform dynamic studies on length scales that are more relevant to real catalysis, allowing for the prediction of catalytic metrics. In particular, we show that the surface chemical heterogeneity of a SAAs results in novel catalytic properties, arising from combined weak adsorption and low activation energies for several bond dissociation reactions; that Pt/Cu SAAs can perform low temperature C-H bond without carbon deposition; and that SAAs offer strong resistivity to catalytic poisoning. Our findings will facilitate the discovery of new alloy catalysts that exhibit novel catalytic behaviour that can be fine-tuned in terms of activity, selectivity and stability.

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