Abstract
The procedures leading to the preservation of catalytic performances of Au/ZrO2 samples have been investigated. The three potential causes of deactivation, namely the particle growth by sintering of gold nanoparticles, the metal leaching and the formation of un-reactive species which inhibit the reaction, have been evaluated. In particular, this paper deals with the stability of gold nanoparticles: (1) under storage conditions; (2) with time on stream for a gas phase reaction (LT-WGSR); (3) with time on stream for a liquid phase reaction (furfural oxidative esterification).
Highlights
The good catalytic activity displayed by highly dispersed gold in many reactions was not expected, considering that gold is the most noble of all metals and it is the least reactive metal towards atoms or molecules at the interface with gases or liquids
A very general phenomenon related to gold samples is the extreme dependence of the catalytic activity on the size of the Au particles, which implies that sintering is very crucial for the long-term stability of the catalysts
Au/ZrO2 materials are of significant interest as catalysts for CO oxidation [7], butadiene hydrogenation [8], epoxidation of styrene [9], low-temperature water–gas shift (LT-WGS) reaction [10,11,12]
Summary
The good catalytic activity displayed by highly dispersed gold in many reactions was not expected, considering that gold is the most noble of all metals and it is the least reactive metal towards atoms or molecules at the interface with gases or liquids. The surprise was enormous when Professor Haruta and co-workers discovered in the late 80s [1] that suitable prepared gold supported on a metal oxide showed high activity in the CO oxidation reaction at temperatures as low as 200 K. A very general phenomenon related to gold samples is the extreme dependence of the catalytic activity on the size of the Au particles, which implies that sintering is very crucial for the long-term stability of the catalysts. These features make Au very different from classical catalysts based on transition metals such as Pt or Pd, which are active as larger particles and even as macroscopic single crystals. Another relevant aspect that must be considered, looking at the application of gold catalysts, is that both activity and stability of these systems strongly depend on the structure of the support as well as on the specific interaction between the gold and the support, giving rise to a synergistic effect
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