Stable mass-selected AuTiO x nanoparticles for CO oxidation.

Stability under reactive conditions poses a common challenge for cluster- and nanoparticle-based catalysts. Since the catalytic properties of <5 nm gold nanoparticles were first uncovered, optimizing their stability at elevated temperatures for CO oxidation has been a central theme. Here we report direct observations of improved stability of AuTiO x alloy nanoparticles for CO oxidation compared with pure Au nanoparticles on TiO 2 . The nanoparticles were synthesized using a magnetron sputtering, gas-phase aggregation cluster source, size-selected using a lateral time-of-flight mass filter and deposited onto TiO 2 -coated micro-reactors for thermocatalytic activity measurements of CO oxidation. The AuTiO x nanoparticles exhibited improved stability at elevated temperatures, which is attributed to a self-anchoring interaction with the TiO 2 substrate. The structure of the AuTiO x nanoparticles was also investigated in detail using ion scattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The measurements showed that the alloyed nanoparticles exhibited a core-shell structure with an Au core surrounded by an AuTiO x shell. The structure of these alloy nanoparticles appeared stable even at temperatures up to 320 °C under reactive conditions, for more than 140 hours. The work presented confirms the possibility of tuning catalytic activity and stability via nanoparticle alloying and self-anchoring on TiO 2 substrates, and highlights the importance of complementary characterization techniques to investigate and optimize nanoparticle catalyst designs of this nature.