Catalysis: Core-shell nanoparticles, catalytic alloys

Heterogeneous catalysts have proven remarkably successful in catalysing a wide range of important processes, in fuel-cells, exhaust emission control and in hydrocarbon processing. However, the effects of the operating environment on the surface composition, structure and stability of the noble metal catalysts that are often employed in alloy form are poorly understood at the atomic-scale. This knowledge will be required to produce the improved catalysts needed for future energy- and materials-efficient technologies.

 

Atom probe tomography (APT) offers a unique method for studying these materials, offering atomic-scale chemical identities of the catalyst surfaces and chemisorbed species. We have used APT to show a rich variety of behaviour in Pt-based alloys, investigating the effects of high temperature/pressure oxidation. These reveal pronounced surface segregation behaviour, strongly dependent on the treatment conditions, crystallographic plane and alloy composition. Recent work has combined APT with other high resolution characterization techniques to invesitgate early stages of oxidation in ternary alloys gauzes.

 

In conjunction with Prof. Tsang in the Inorganic Chemistry Department (http://tsang.chem.ox.ac.uk/Group.htm), we are also undertaking research using a range of sample preparation methods to exploit APT for characterizing catalytic nanoparticles. We can now also analyse commercial catalyst nanoparticles, even on carbon supports, and correlate their atomic-scale properties with performance.

Core-shell structure of Ag@Pd catalysts for room-temperature H2 production

APT reconstructions of Pt-Rh oxidized for 5 hours, Pt-Pd for 5 hours and Pd-Rh for 3 hours, all at 873K in 1bar O2

For more details on this project, please contact  Dr. Michael Moody.