A Rational Design of the Sintering-Resistant Au-CeO₂ Nanoparticles Catalysts for CO Oxidation: The Influence of H₂ Pretreatments.

Yuqi Sun,Liguo Wang,Zhongpeng Wang,Miao Tian,Wei Liu

doi:10.3390/ma11101952

Abstract

The redox pretreatment of samples is one of the crucial ways of altering the catalytic properties of the supported noble metal materials in many heterogeneous reactions. Here, H2-reducing pretreatment is reported to enhance the thermal stability of Au-CeO2 catalysts prepared by the deposition–precipitation method and calcination at 600 °C for CO oxidation. In order to understand the improved activity and thermal stability, a series of techniques were used to characterize the physico-chemical changes of the catalyst samples. H2 pretreatment may lead to: (i) a strong metal–support interaction (SMSI) between Au nanoparticles (NPs) and CeO2, evidenced by the particular coverage of Au NPs by CeO2, electronic interactions and CO adsorption changes. (ii) the production of surface bicarbonates which can accelerate CO oxidation. As a result, the H2 pretreatment makes the Au NPs more resistant to sintering at high temperature and enhances the CO oxidation activity. Furthermore, this reduction pretreatment strategy may provide a potential approach to enhance the thermal-stability of other supported noble metal catalysts.

Highlights

In heterogeneous catalytic reactions, the Au nanoparticles (NPs), as the active species with superior catalytic activities, have been attracted considerable interests in recent decades
For various times, followed by pretreated upon H2 atmosphere at 200 ◦ C. These products were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, high-resolution transmission electron microscope (HRTEM), in-situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectra (XPS) to elucidate the effect of H2 pretreatments on the catalytic performance of CO oxidation
Catalytic CO oxidation is used as a probe reaction to investigate the relations between the pretreatment conditions and the catalytic properties of the Au-CeO2 catalysts

Summary

Introduction

The Au nanoparticles (NPs), as the active species with superior catalytic activities, have been attracted considerable interests in recent decades. Because the Au NPs calcined at high temperatures are agglomerated after pretreatments [15], there are few efficient methods to improve the thermal stability of Au NPs with reduction conditions. Inspired by previous research results, H2 -reducing pretreatment method was used to fabricate SMSI in the Au-CeO2 catalysts further to trace whether the Au NPs can be stabilized while holding their high activity. In our study, the Au-CeO2 spheres calcined at 600 ◦ C for various times, followed by pretreated upon H2 atmosphere at 200 ◦ C These products were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, high-resolution transmission electron microscope (HRTEM), in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) and X-ray photoelectron spectra (XPS) to elucidate the effect of H2 pretreatments on the catalytic performance of CO oxidation. The H2 pretreatment makes the Au NPs more resistant to sintering at high temperatures, which may be extended to other supported noble metal catalysts

Materials

The Synthesis of Au-CeO2 Samples

Characterization

Catalytic Tests

Results and Discussion

Conclusions