Abstract
The purpose of the study was to show how a controlled, subtle change of the reducibility of the support by deposition of potassium ions impacts the activity of gold catalysts. Since the activity of supported gold catalysts in carbon monoxide oxidation is known to strongly depend on the reducibility of the support, this reaction was chosen as the model reaction. The results of tests conducted in a simple system in which the only reagents were CO and O2 showed good agreement with the CO activity trend in tests performed in a complex stream of reagents, which also contained CH4, C2H6, C3H8, NO, and water vapor. The results of the X-ray Diffraction (XRD) studies revealed that the support has the composition Ce0.85Zr0.15O2, that its lattice constant is the same for all samples, and that gold is mostly present in the metallic phase. The reducibility of the systems was established based on Temperature Programmed Reduction (TPR) and in situ XRD measurements in H2 atmosphere. The results show that the low temperature reduction peak, which is due to the presence of gold, is shifted to a higher value by the presence of 0.3 at% potassium ions on the surface. Moreover, the increase of the potassium loading leads to a more pronounced shift. The T50 of CO oxidation in the simple model stream was found to exhibit an excellent linear correlation with the maximum temperature of the low temperature reduction peak of Au catalysts. This means that stabilizing oxygen with a known amount of potassium ions can be numerically used to estimate the T50 in CO oxidation. The results in the complex stream also showed a similar dependence of CO conversion on reducibility, though there was no substantial difference in the activity of the catalysts in other reactions regardless of the potassium loading. These studies have shown that the influence of potassium varies depending on the reaction, which highlights differences in the impact of reducibility and importance of other factors in these reactions.
Highlights
Due to the fact that supported gold catalysts exhibit well-documented high activity in low temperature CO oxidation [1,2,3,4] they are commonly studied for automotive applications, despite the fact that the platinum, palladium, and ruthenium catalysts are highly active in the combustion of hydrocarbons [5]
They show that the main phase present in these systems is the ceria-zirconia solid solution with ions
The doping of gold catalysts with potassium ions was applied to investigate the extent of stabilizing oxygen species of the support, i.e., decreasing its reducibility, and the effect on the loss of activity in CO oxidation, where support reducibility plays a crucial role
Summary
Due to the fact that supported gold catalysts exhibit well-documented high activity in low temperature CO oxidation [1,2,3,4] they are commonly studied for automotive applications, despite the fact that the platinum, palladium, and ruthenium catalysts are highly active in the combustion of hydrocarbons [5]. The change of the support composition has a substantial impact on the reducibility of the system, and on variables such as: lattice parameter of the support and the interaction of gold with the support, etc. This is why the goal of this study was to prepare a specific fraction of one batch of the calcined support with a specific composition, onto which first gold was deposited, followed by the deposition of potassium ions, so that the obtained systems would differ mainly in the potassium loading
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