We combine synthetic surface chemistry and a variety of advanced characterization methods including nonlinear spectroscopy to demonstrate an example in which we bridge the gap between realistic complex catalyst materials and methods used to elucidate their surface chemistry, and do so at the liquid/solid interface. Sum frequency generation is used to determe the adsorption behavior of 1-hexanoic acid, the important overoxidation product in alcohol oxidation over Pd catalysts, on the surfaces of aluminum oxide-supported nanometer sized palladium nanoparticles prepared by atomic layer deposition. The adsorption of 1-hexanoic acid is shown to occur on ALD alumina surfaces, and on ALD alumina surfaces with palladium nanoparticles. 1-hexanoic acid becomes more ordered with increasing adsorbate concentration for surfaces containing 3 nm Pd particles, but molecular ordering does not increase with concentration for surfaces with smaller palladium particles or no palladium particles. Thus, even though adsorption isotherms do not indicate a significant role for palladium in modulating adsorption energy for 1-hexanoic acid, the palladium particles play a role in interacting with adsorbates to modulate their structures. Furthermore, 1-hexanoic acid is shown to have a much higher binding constant than 1-hexanol, and leads to its displacement in competitive adsorption experiments. Since carboxylic acids are known to be over-oxidation products of selective oxidation reactions, their relative binding strengths in relation to alcohols is important for predicting catalytic reaction rates, and catalyst poisoning due to site-blocking. The implications for exploiting synergistic effects of adsorbate binding strength and the molecular structures they adopt on catalysts containing mixed metal nanoparticles supported on mixed oxides for suppressing catalyst deactivation through poisoning are discussed.

Molecular origin of catalyst poisoning of supported Pd nanoparticle catalysts in heterogeneous alcohol oxidation under liquid hexaneby vibrational sum frequency generation

243rd National Meeting (2012)

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