Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

The recent availability of shale gas has led to a renewed interest in C-H bond activation as the first step towards the synthesis of fuels and fine chemicals. Heterogeneous catalysts based on Ni and Pt can perform this chemistry, but deactivate easily due to coke formation. Cu-based catalysts are not practical due to high C-H activation barriers, but their weaker binding to adsorbates offers resilience to coking. Using Pt/Cu single-atom alloys (SAAs), we examine C-H activation in a number of systems including methyl groups, methane and butane using a combination of simulations, surface science and catalysis studies. We find that Pt/Cu SAAs activate C-H bonds more efficiently than Cu, are stable for days under realistic operating conditions, and avoid the problem of coking typically encountered with Pt. Pt/Cu SAAs therefore offer a new approach to coke-resistant C-H activation chemistry, with the added economic benefit that the precious metal is diluted at the atomic limit.

Platinum catalysts are extensively used in the chemical industry and as electrocatalysts in fuel cells. Pt is notorious for its sensitivity to poisoning by strong CO adsorption. Here we demonstrate that the single-atom alloy (SAA) strategy applied to Pt reduces the binding strength of CO while maintaining catalytic performance. By using surface sensitive studies, we determined the binding strength of CO to different Pt ensembles, and this in turn guided the preparation of PtCu alloy nanoparticles (NPs). The atomic ratio Pt:Cu = 1:125 yielded a SAA which exhibited excellent CO tolerance in H2 activation, the key elementary step for hydrogenation and hydrogen electro-oxidation. As a probe reaction, the selective hydrogenation of acetylene to ethene was performed under flow conditions on the SAA NPs supported on alumina without activity loss in the presence of CO. The ability to maintain reactivity in the presence of CO is vital to other industrial reaction systems, such as hydrocarbon oxidation, electrochemical methanol oxidation, and hydrogen fuel cells.

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Key descriptors in hydrogenation catalysis are the nature of the active sites for H2 activation and the adsorption strength of H atoms to the surface. Using atomically resolved model systems of dilute Pd-Au surface alloys and density functional theory calculations, we determine key aspects of H2 activation, diffusion, and desorption. Pd monomers in a Au(111) surface catalyze the dissociative adsorption of H2 at temperatures as low as 85 K, a process previously expected to require contiguous Pd sites. H atoms preside at the Pd sites and desorb at temperatures significantly lower than those from pure Pd (175 versus 310 K). This facile H2 activation and weak adsorption of H atom intermediates are key requirements for active and selective hydrogenations. We also demonstrate weak adsorption of CO, a common catalyst poison, which is sufficient to force H atoms to spill over from Pd to Au sites, as evidenced by low-temperature H2 desorption.

Platinum is a key component in many heterogeneous hydrogenation catalysts. Because of its high price, fairly strong interaction with intermediates, and susceptibility to CO poisoning, it is often mixed with other elements. These bimetallic alloys have complex surface structures, and the atomic structure of their active sites is not well understood. In this study, we examine the effect of the geometric arrangement of dilute Pt−Cu alloys on H 2 activation, spillover, and release. Using scanning tunneling microscopy, we directly visualize the atomic arrangement of Pt−Cu alloys and show that small amounts of Pt (∼1%) exists as isolated atoms in the Cu surface. These Pt monomers are capable of facile H 2 dissociation and spillover to Cu at temperatures as low as 85 K. Additionally, the low-temperature desorption of H 2 (230 K) suggests a reduced desorption barrier compared to monometallic Pt or Cu. We find these single atom alloy surfaces are robust to multiple adsorption/desorption and heating cycles to 450 K. Larger Pt ensembles in Cu exhibit higher temperature desorption profiles due to the stronger binding of H to extended Pt ensembles, demonstrating how the geometric arrangement of Pt atoms in Cu impacts the binding of H to catalytic surface sites. Overall, dilute Pt−Cu alloys containing only isolated Pt atoms are most favorable for H 2 activation, spillover, and release and hence should be capable of catalyzing hydrogenation reactions with a greatly reduced concentration of the precious metal.

Pt–Cu bimetallic alloys are a key component in many heterogeneous catalysts that have the potential to be used in a range of industrially important reactions. Given the catalytic differences between Pt and Cu, the surface composition and geometry of Pt–Cu alloys can have a large influence on their chemistry. Extensive characterization of bulk Pt–Cu alloys has been performed; however, only a few studies have addressed surface and subsurface alloying of Pt with Cu, and none have examined the atomic scale surface structure of Pt–Cu. In this study, scanning tunneling microscopy was used to determine the local structure of surface alloys formed by physical vapor deposition of Pt onto Cu(111) over a range of alloying temperatures (315–550 K). Our results indicated that Pt and Cu were capable of intermixing at 315 K and forming multiple metastable states. Increasing the temperature of the Cu surface during the deposition of Pt altered the surface geometry and further enhanced the dispersion of Pt. The results are compared to the well-characterized Pd/Cu(111) surface alloy. A distinguishing feature of the Pt/Cu(111) surface alloy is the ability of Pt atoms to alloy directly into the Cu surface. Pt alloys as individual isolated atoms, well separated from each other, rather than more localized in regions at step edges, as is the case with Pd. This work indicates that the highly dispersed nature of Pt–Cu surface alloys should render them useful for understanding the surface chemistry of Pt at the single atom level.

Silica supported and unsupported PdAu single atom alloys (SAAs) were investigated for the selective hydrogenation of 1-hexyne to hexenes under mild conditions.