Controlling Nanoscale Properties of Supported Platinum
Catalysts through Atomic Layer Deposition
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Abstract
Platinum nanoparticles
were grown on alumina by atomic layer deposition
using either H<sub>2</sub> or O<sub>2</sub> as the second half-reaction
precursor. Particle diameters could be tuned between ∼1 and
2 nm by varying between use of H<sub>2</sub> and O<sub>2</sub> and
by changing the number of ALD cycles. The use of H<sub>2</sub> as
the second precursor led to smaller Pt particle sizes. Differences
in particle size were found to be related to the availability of surface
hydroxyl groups, which were monitored via in situ infrared spectroscopy
during Pt ALD. Temperature-programmed desorption (TPD) of CO and diffuse
reflectance infrared Fourier transform spectroscopy (DRIFTS) for adsorbed
CO were used to characterize sites and coordination numbers of the
nanoparticles. As expected, smaller nanoparticles had sites with lower
average coordination numbers. The catalysts were evaluated for oxidative
dehydrogenation of propane to propylene. Catalysts having the smallest
Pt particles with the lowest coordination number (synthesized by one
cycle of Pt ALD with H<sub>2</sub>) had a C<sub>3</sub>H<sub>6</sub> selectivity of 37% at 14% conversion, whereas under the same reaction
conditions the selectivity was less than 1% for larger (3.6 nm) commercial
Pt catalysts at 9% conversion