Synthesis of Platinum Catalysts over Thick Slurries of Oxide Supports by Strong Electrostatic Adsorption

Platinum uptake by strong electrostatic adsorption on alumina, silica, and titania supports was studied at different slurry thicknesses (or surface loadings). For the anionic platinum chloride precursor, a high counterion concentration at high surface loadings hindered adsorption on the high point of zero charge alumina support, as predicted by the revised physical adsorption model. Owing to this adsorption retardation in thicker slurries, a highly dispersed Pt/Al2O3 catalyst could only be prepared with a lower weight fraction of Pt than that in thin slurries. However, for cationic platinum tetraamine complexes, the effect of counterions in retarding the adsorption at high surface loadings was unexpectedly diminished. As a result, it was possible to synthesize highly dispersed Pt/SiO2 even at a maximum slurry thickness (incipient wetness) without having to sacrifice the Pt loading.