Controlling Nanoscale Properties of Supported Platinum Catalysts through Atomic Layer Deposition

Platinum nanoparticles were grown on alumina by atomic layer deposition using either H-2 or O-2 as the second half-reaction precursor. Particle diameters could be tuned between similar to 1 and 2 nm by varying between use of H-2 and O-2 and by changing the number of ALD cycles. The use of H-2 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-2) had a C3H6 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.