Understanding a catalyst from formula to mechanism
09 Nov 2011



Neutron and x-ray powder diffraction and several other techniques are used to characterise hydrous palladium oxide, a key component of catalytic converters.

The structure of hydrous palladium oxide's core. Neutron diffraction, using Gem, defines the PdO core.

Palladium catalysts are a key component of the three-way catalytic converter used in cars, where they effect complete oxidation of hydrocarbons and carbon monoxide. To discover the effect of
palladium, we have investigated the low-temperature catalytic conversion of carbon monoxide over hydrous palladium oxide powders. This oxidation reaction is remarkable in that it readily occurs at room temperature and pressure. However, almost all that has been known about hydrous palladium oxide is its empirical formula, namely, PdO•H2O.

We have characterised the material using a combination of neutron and x-ray powder diffraction, transmission electron microscopy, inelastic neutron scattering spectroscopy, infrared spectroscopy and computational methods. The results show that the material is best described as PdO nanocrystallites around 2 nm in size, terminated by a monolayer or so of hydroxyl groups, and capped by 4-7 layers of water. This model allows us to gain insight into the mechanism of catalytic oxidation of CO over a supported palladium catalyst. 

SF Parker, AC Hannon, E Barney (ISIS), K Refson (CSE-RAL), SJ Robertson (AMG-RAL), P Albers (AQura GmbH

Research date: August 2011

Further Information

Contact: Dr SF Parker, stewart.parker@stfc.ac.uk

Further reading: SF Parker et al., J Phys Chem C 114 (2010) 14164​