Preparation of well-dispersed Pt/SiO2 catalysts using low-temperature treatments.

This work explores methods to prepare platinum on silica catalyst using temperatures as low as possible. Therefore, thermal stability in both oxidizing and reducing atmosphere of eight different precursors was studied with thermo-gravimetric analyses (TGA-MS). Based on these data, the precursors were tested to prepare silica supported catalysts, resulting in relationship between the thermal stability of the precursors, the procedures of impregnation, reduction and calcination with the final dispersion on silica. Platinum precursors decomposed more easily in reducing than in oxidizing environment, due to thermochemistry. Catalysts prepared by using ion-exchange and direct reduction in hydrogen resulted in highly dispersed platinum particles on silica. PtClx and PtOx species, when present during catalyst preparation, cause sintering of platinum at temperatures higher than 250 °C (PtClx) and 350 °C (PtOx), respectively. These species can be converted more easily in hydrogen than in air. PtCl4, H2PtCl6·6H2O and H2Pt(OH)6 are suitable as precursors for achieving high platinum dispersion, keeping temperatures below 150 °C.