Surface analysis of thermally stable Pt loaded CeO2–ZrO2 using colloidal Pt for TWC application

Abstract

Suppressing Pt aggregation is the most effective way to prepare highly active Pt-based three-way catalysts (TWCs), as Pt aggregation easily occurs during driving operations. As previously reported, forming a strong interaction between Pt and CeO₂ is a promising method to suppress aggregation in TWCs. In this study, we utilize different Pt precursors to modify the interaction in Pt-loaded CeO₂–ZrO₂ (Pt/CZ). In fact, Pt/CZ prepared using colloidal Pt (C-Pt) exhibits significantly higher catalytic activity for purifying exhaust gas emissions than conventional Pt/CZ prepared using dinitrodiammine Pt (Pt-P) after aging treatment at 1000 °C under air. However, aging treatment under N₂ leads to the opposite result. IR analyses using CO as a probe gas indicated that the oxidation state of Pt derived from Pt-P was strongly affected by the atmosphere during aging treatment. The Pt particles formed on the surface of CZ from Pt-P were easily oxidized under air aging, often causing serious Pt aggregation. On the other hand, Pt particles dispersed on CZ as C-Pt were hardly affected. Further analyses such as TPR and IR using methanol as a probe molecule revealed that changes in the redox properties were attributed to the different amounts of boundary between Pt and CZ. The results suggest that the interface between Pt and CZ should be limited when oxidative operating conditions are expected because the extensive boundary provokes serious Pt aggregation.