Bridging the pressure and materials gaps: High pressure sum frequency generation study on supported Pd nanoparticles

Infrared-visible sum frequency generation vibrational spectroscopy is applied for the first time to monitor CO stretching vibrations on alumina supported Pd nanoparticles in a pressure range from 10(-7) to 200 mbar. The adsorption behavior of Pd aggregates with 3 and 6 nm mean size is dominated by surface defects and two different adsorption sites (twofold bridging and on-top) were identified. The CO adsorption site occupancy on Pd nanocrystals is mainly governed by the gas phase pressure while the structure of the particles and their temperature have a smaller influence.