AuPd/TiO2 Catalysts in the CO Oxidation: Insights into the Synthesis Procedure and In-situ Spectroscopy Studies

Abstract

A series of bimetallic AuPd/TiO2 catalysts (Au/Pd = 1) were prepared through either the impregnation or the deposition-precipitation in urea (DPU) approach and tested in the CO oxidation reaction. Among these, the sample synthesized through a sequential impregnation (Pd) followed by DPU (Au), with an intermediate thermal treatment in air, presented a remarkable CO conversion at sub-ambient temperatures and an enhanced catalytic stability, compared to the monometallic samples. The ex-situ characterization revealed that the synthesis procedure led to the formation of well-dispersed bimetallic AuPd nanoparticles over the TiO2 support. The in-situ characterization helped to propose that bimetallic NPs were composed of an intermetallic Au-Pd phase with both atoms available in the surface. Both in-situ FTIR and UV-vis spectroscopies helped to recognize the active sites during the reaction: Au in close interaction with the TiO2 at low temperatures, and step/edges Pd sites at high temperatures. Finally, the pivotal role of the TiO2 reducibility in the CO oxidation reaction, promoted by the bimetallic AuPd NPs, was determined through in-situ Raman spectroscopy.