On the behaviour of structure-sensitive reactions on single atom and dilute alloy surfaces

Highly dilute alloys and single-atom alloys (SAAs; a subclass of dilute alloys in which the minority metal is atomically dispersed) have attracted significant interest in view of their remarkable catalytic properties. Indeed, an increasing amount of data gathered from surface science and catalysis studies shows that they exhibit high activity and selectivity in a number of reactions, e.g. C-H activation, C-C coupling, (de)hydrogenation reactions and catalytic oxidations, as well as high resistance to poisons such as coke and CO. However, most of the surface science experiments and the theoretical studies have so far focused on the most stable surface geometry, i.e. the (111) crystal facet. On the other hand, practical catalysts expose other surfaces as well, and it is therefore important to elucidate the catalytic behaviour of these alloys on these surfaces.

Thus motivated, a recent theoretical study from Michail Stamatakis's group, which was featured in the cover of Catalysis Science and Technology, focused on reactions that exhibit structure-sensitivity on "traditional" catalysts and are of interest to vehicle emissions control. In particular, the reactions considered include the direct dissociations of NO, CO2 and N2, and the reverse events (association reactions). The study demonstrates that the structure-sensitivity of the dissociation reactions is considerably reduced on SAA surfaces as compared to pure platinum group metal surfaces (Rh, Pt, Pd and Ni). This property of SAAs is important from a practical standpoint, since it could eliminate the need for precise engineering of the structure and geometry of catalytic nanoparticles, making the process of catalyst manufacturing simpler and more economical. Additionally, the study identified highly dilute alloys consisting of small Ni clusters (dimers and trimers) doped on Cu(100) and (111) facets, as excellent catalysts for the activation of N=O and C=O bonds, but also for the formation of N2 which is a crucial reaction for the efficient operation of three-way catalytic converters. These highly dilute alloys were shown to outperform the SAAs studied and exhibit similar (or even better in some cases) catalytic properties than well-established pure metals in heterogeneous catalysis (e.g. Rh, Pt and Pd).

This work can therefore guide future theoretical, surface science and catalysis studies on SAAs and highly dilute alloys, towards the development of superior catalysts that can efficiently catalyse chemistries of industrial significance.



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