Industrial heterogeneous catalysts ubiquitously contain trace amounts (ppm) of “promoters” species, which can substantially promote activity, selectivity, or stability. Recently, it has been observed that the addition of very small amounts (<1:100 atom %) transition metal atoms (e.g. Pt, Pd, Ni) to coinage metal (Au, Ag and Cu) surfaces can drastically promote selectivity in hydrogenation and dehydrogenation catalysis. The unique catalytic behavior of these ultra-dilute alloys derives from bifunctional reaction pathways where molecular activation at the dispersed promoter sites results in intermediate spillover onto the coinage metal host, enabling distinct reactivities.
Here, I will discuss another promotional influence of ultra-dilute alloys – promoting the sintering resistance of supported Cu-based alloys. We observed that the addition of just 1:100 ratio of Pt or Rh to ~2-3 nm Cu nanoparticles substantially slows the rate of Cu sintering during accelerated aging. A combination of theory, surface science, in-situ spectroscopy and high surface area catalyst measurements were used to design and understand the function of the dilute stability promoters. We conclude that the promoter dopants function to stabilize step and edges sites on Cu nanoparticles and thus the rate of the first step involved in nanoparticle sintering by Ostwald ripening. These findings demonstrate that dilute alloy catalysts have potential to improve catalyst performance beyond hydrogenation/dehydrogenation chemistries and that they offer potential for simultaneous promotion of rate/selectivity and stability.
