Abstract
Gold-iron oxide (Au/FeOx) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O), have been used for the deposition of gold via a deposition-precipitation (DP) method. The structure of iron oxide has been tuned by either selecting precipitated pH of 6.7–11.2 for Fe_OH or changing calcination temperature of from 200 to 600 °C for Fe_O. Then, 1 wt. % Au catalysts on these iron oxide supports were measured for low-temperature CO oxidation reaction. Both fresh and used samples have been characterized by multiple techniques including transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and temperature-programmed reduction by hydrogen (H2-TPR). It has been demonstrated that the surface properties of the iron oxide support, as well as the metal-support interaction, plays crucial roles on the performance of Au/FeOx catalysts in CO oxidation.
Highlights
Since the 1990s, nanosized gold interacting with oxide supports have been reported to be active for diverse redox reactions, among those low temperature oxidation of carbon monoxide is the most studied [1,2,3]
Hutchings group reported that the delayered Au structure that was determined by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization plays crucial roles in the CO oxidation reaction [8]
For Au/FeOx supports include two different types: hydrated (Fe_OH) series, the SBET number decreases with the increase of precipitating pH value of Fe_OH from 6.7 to 11.2, possibly indicating better crystallinity of iron oxide support with more hydroxyls used in preparation
Summary
Since the 1990s, nanosized gold interacting with oxide supports have been reported to be active for diverse redox reactions, among those low temperature oxidation of carbon monoxide is the most studied [1,2,3] Such unique catalytic properties were found to be strongly dependent on electronic structure and local coordination environment of Au atoms. Different techniques, including X-ray diffraction (XRD) [25], X-ray absorption fine structure (XAFS) [16], X-ray photoelectron spectroscopy (XPS) [16] and transmission electron microscopy (TEM) [28], have been used to characterize both bulk and surface structure of gold-iron oxide catalysts and further study the related active site for the low-temperature CO oxidation. In the present work, we try to broadly explore the relationship between the nature of the oxide matrix and the catalytic reactivity of Au/FeOx via deposition-precipitation with two series of iron oxides, namely hydrated (Fe_OH) and dehydrated (Fe_O) supports, to fully investigate the importance of preparation parameters such as precipitating pH values and calcination temperature in synthesis of FeOx , and to deeply study the “structure-activity” relationship in Au/FeOx system for the low-temperature CO oxidation reaction
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