Preparation of Pd–MgO model catalysts by deposition of Pd from aqueous precursor solutions onto Ag(0 0 1)-supported MgO(0 0 1) thin films

• Surface science approach to catalyst preparation.
• Thin, single crystalline MgO(0 0 1) films were utilized as substrate for the preparation of supported Pd model catalysts.
• Dissolution of MgO in acidic and neutral environments limits the applicability of Pd precursors.
• Thermal decomposition of Pd-hydroxide precursor yields contaminant-free Pd nanoparticles.
• Morphological and chemical properties of UHV-derived and aqueous precursor-derived Pd–MgO model catalysts are similar.

The preparation of Pd–MgO model catalysts via liquid-phase deposition of Pd from aqueous Pd precursor solutions was studied. Thin, single-crystalline MgO(0 0 1) films grown on a Ag(0 0 1) substrate were used as support and allowed surface science techniques such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature programmed desorption to be applied for characterization. Thin MgO(0 0 1) films were unstable and rapidly dissolved in acidic and neutral environments, but remained stable in thickness in alkaline solutions after an initial dissolution of a few layers of MgO. Pd was deposited by exposure of the thin film MgO substrate to alkaline (pH 12) precursor solutions containing Pd-hydroxide complexes. Scanning tunneling microscopy images taken from ultrathin MgO films revealed the formation of Pd particles 3 nm in diameter after thermal decomposition of the precursor at 600 K, as well as roughening of the MgO substrate, including the formation of etch pits, which leads to partial exposure of the Ag substrate. For Pd deposited on thick MgO films, the formation of Pd nanoparticles by thermal decomposition of the adsorbed Pd-hydroxide precursor was followed by X-ray photoelectron spectroscopy. Pd–MgO model catalysts with similar Pd coverage prepared either by liquid-phase deposition or physical vapor deposition in UHV exhibited similar properties, as revealed by their comparable behavior in CO adsorption and CO oxidation.

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