(499d) Selective Dehydrogenation and Oxidation Reactions on Niau Alloys at the Single Atom Limit

Gold, while inert as a bulk metal, shows significant activity and selectivity when in nanoparticle (< 5 nm dia.) form[1]. Despite its high selectivity, monometallic Au is less active than commercial catalysts in reactions of industrial importance, such as the dehydrogenation of ethanol to acetaldehyde and the oxidative methanol-methacrolein esterification to methyl methacrylate. Therefore, the addition of a metal able to coordinate and activate unsaturated organic compounds (e.g. alcohols), such as Ni, could lead to improved catalyst reactivity. Atomically embedded Ni in Au surfaces would form an alloy at the atomic level (Single Atom Alloy), which allows us to reap the benefits of the high selectivity of Au coupled with the remarkable activity of Ni, thus obtaining better catalysts than their monometallic counterparts.

In the present work, we compare various NiAu structures, prepared as Ni-Au nanoparticles (NPs) supported on SiO₂, unsupported Ni-doped nanoporous Au (np-NiAu) and the industrially used Au@Ni core-shell catalyst[2]. The formation of highly dilute Ni-Au alloys is followed by CO-DRIFTS. Temperature Programmed Surface Reaction studies on ethanol dehydrogenation show 100% selectivity and noticeable stability for the NPs and np-NiAu materials. Kinetic measurements find the SAA NiAu to be more active than gold, and further show that the increased activity is induced by Ni, as the apparent activation energy values are lower for the SAA than for the monometallic Au samples. Comparison between Ni-Au NPs and the commercial catalyst was made via in situ ATR-IR spectroscopy combined with HPLC for the oxidative methacrolein-methanol coupling reaction in the liquid phase. The catalyst structure and composition was also followed by ICP, STEM/EDS and XAS.

Acknowledgements:This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award #DESC0012573.

References

1. M. Haruta, N. Yamada, T. Kobayashi and S. Iijima, J. Catal., 1989, 115, 301-309.
2. K. Suzuki, T. Yamaguchi, K. Matsushita, C. Iitsuka, J. Miura, T. Akaogi and H. Ishida, ACS Catal., 2013, 3, 1845-1849