Preparation of platinum-on-carbon catalysts via hydrolytic deposition: Factors influencing the deposition and catalytic properties

The deposition of Pt oxide from aqueous chloroplatinate solutions onto carbon supports (activated carbons, carbon blacks, carbon nanofibers) with the aid of Na2CO3 and without adding the reductants or wetting agents was studied. It has been revealed that carbons accelerate greatly the hydrolysis of chloroplatinate, and the hydrolytic deposition can therefore interfere with the other preparation methods. Neutral pH was found optimum for heterogeneous nucleation and formation of smaller PtOx particles. High temperature (80 °C) allowed depositions of 5–30 wt.% of Pt for a short time (1–3 h) but did not affect Pt dispersions (15–90% at surface concentration of Pt 0.5–30 μmol/m2). The supported particles could be further reduced in the liquid phase with minimal losses of the dispersion (Na-formate as reductant). The heterogeneous nucleation ensured a uniform distribution of Pt particles but provoked particle confinement in narrow pores. The possibility of influencing catalytic properties with the aid of the support, Pt loading and deposition conditions was demonstrated (hydrogenation of cycloalkenes as a model structure-insensitive reaction and oxidation of isopropyl alcohol as structure-sensitive one).

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► Strong promotion of the chloroplatinate hydrolysis by carbons.
► Rapid hydrolytic depositions at neutral pH.
► Small Pt particles, high Pt loadings, uniform distribution over the support.
► Occurrence of pore-size effect.
► Possibility of tuning catalytic properties.