Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments.

Ekaterina Kolobova,Yulia Kotolevich,Mario Farías,Grigory Mamontov,Vicente Cortés Corberán,Alexey Pestryakov,Ekaterina Pakrieva,Nina Bogdanchikova

doi:10.3390/molecules21040486

Abstract

The catalytic properties of modified Au/TiO2 catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H2 TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au+. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity.

Highlights

The activity of catalysts based on gold nanoparticles is unique, as these catalytic systems can operate at ambient or even lower temperatures, which is crucial for a number of important industrial and environmental processes
The discovery of Haruta in the eighties of the last century that the gold deposited on metal oxides is active in the oxidation of CO at temperatures below ambient, together with works of Hutchings on hydrochlorination of acetylene on gold deposited on the carbon ushered in a new era—the era of “gold catalysis”
In the as-prepared state, catalyst with the unmodified support is the most active, while those supported on modified titanias show little activity at low temperatures

Summary

Introduction

The activity of catalysts based on gold nanoparticles is unique, as these catalytic systems can operate at ambient or even lower temperatures, which is crucial for a number of important industrial and environmental processes. An increasing number of papers and patents have been published on nanogold catalytic activity. This indicates that there is a great interest in this increasingly promising area of catalysis, both by theorists and by industrialists. Despite the unique catalytic properties of nanogold catalysts, a number of problems remain unsolved. The effect of particle size on the activity: only gold nanoparticles smaller than 5 nm exhibit high activity; according to some research groups

Objectives

Methods

Results

Conclusion