Abstract
The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT) based calculations were considered to clarify the role of the low coordinated gold atoms and the role of doping in the catalytic activity of gold. The effect of the surface steps was introduced by comparison of the activation energy barriers and of the adsorption energies on flat gold surfaces such as the Au(111) surface with those on stepped surfaces such as the Au(321) or the Au(110) surfaces. It is concluded that the presence of low coordinated atoms on the latter surfaces increases the adsorption energies of the reactants and decreases the activation energy barriers. Furthermore, the increasing of the adsorption energy of the reaction products can lead to lower overall reaction rates in the presence of low gold coordinated atoms due to desorption limitations. On the other hand, the effect of doping gold surfaces with other transition metal atoms was analyzed using the dissociation reaction of molecular oxygen as a test case. The calculations showed that increasing the silver content in some gold surfaces was related to a considerable increment of the reactivity of bimetallic systems toward the oxygen dissociation. Importantly, that increment in the reactivity was enhanced by the presence of low coordinated atoms in the catalytic surface models considered.
Highlights
Reactions on gold based catalysts have been intensely studied since the discovery at the end of the eighties that highly dispersed gold nanoparticles on a transition metal oxide support catalyze the oxidation of carbon monoxide, even at temperatures as low as −70 °C [1]
It seems clear that the low coordinated gold atoms have to have a central role in the catalysis as is indicated by the fact that high dispersed gold nanoparticles catalyze the CO oxidation or by the fact that nanoparticles with diameters
We found that increasing the silver content of the gold surfaces significantly affects the catalyst activity for the O2 dissociation (please see Figure 1 which illustrates the effect of the Au(111) surface doping in the catalytic activity)
Summary
Reactions on gold based catalysts have been intensely studied since the discovery at the end of the eighties that highly dispersed gold nanoparticles on a transition metal oxide support catalyze the oxidation of carbon monoxide, even at temperatures as low as −70 °C [1]. The enhancement of the reactivity for the reaction of CO oxidation caused by this type of irregularities on gold based catalysts is very probably related with the presence and concentration of low coordinated metal atoms on the catalytic systems [11,12]. The formation of carbonates, surface species that were experimental detected [14,15], from co-adsorbed CO and O2 surface molecules was found to occur on the catalyst surface [13] Another important reaction studied on gold-based catalysts is that of oxygen dissociation, a crucial step in many oxidation reactions including the oxidation of CO or methanol. Some of the most recent results attained by computational work on some heterogeneous reactions catalyzed by gold surfaces are reviewed, paying special attention to the effect of the low coordinated and doping atoms in the catalytic reactions.
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