Understanding of the activity difference between nanogold and bulk gold by relativistic effects

Abstract

It is a challenge to thoroughly understand the astonishing difference in catalytic activity between nano gold and bulk gold for some oxidation reactions. In this work, the Au-O interactions in various surroundings were investigated by DFT calculations and compared with the Ag-O interactions. We have found the three points. First, only Au-O bond can be significantly strengthened by the linear O-Au-O structure. Second, the Au-O bond is always stronger than the Ag-O bond when the bonds are embedded in common surroundings. Third, the Au-O bond becomes weaker than the Ag-O bond when the number of neighboring Au atoms becomes large, because the Au-O interactions are suppressed by the presence of neighboring gold atoms. The origin of © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ these three points can be attributed to wider spatial extension of d orbitals of gold, induced by strong relativistic effects. The strong relativistic effects make nano gold with smaller coordinate numbers highly active due to the ease in forming strong Au-O bonds, especially for the O-Au-O bond, whereas gold atoms in bulk with larger coordination numbers chemically inert due to the strong suppression by neighboring gold atoms destabilizing the O-Au-O bond.

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“…Hence, despite the intrinsically stronger Au–O bond, the Au–O bond in Au x –O usually appeared to be weaker than the Ag–O bond in Ag x –O. 49 In this case, formation of the Au–O bond between the e-AuNPs and cellulose fibers of the filter paper could have been suppressed by many neighboring atoms, and therefore, it was weaker than the Ag–O bond. Hence, there were only a few e-AuNPs attached onto the surface of the filter paper.…”

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“…However, as shown in the Fig. S10 (ESI †), the 3D islands of the 1 nm Au on the Bis-FIMG are significantly smaller than those of the 1 nm Ag due to the interaction between Au-O and Au-I being stronger than Ag-O and Ag-I, 50 which will provide a higher nucleation density for the growth of ultra-thin Ag films and make the Ag films more uniform. Second, at the same time, since the surface energy of Au is higher than that of Ag (1.5 J m À2 vs. 1.25 J m À2 ), when the ultra-thin Ag films are deposited on the Au seed layer, the growth mode of ultra-thin Ag will be transformed into a Frank-van der Merwe mechanism (layer by layer growth).…”

Gold-Catalysed Reactions

“…It seems that other reactions such as hydrogen oxidation to hydrogen peroxide, organic oxidation and hydrogenation may follow a similar pattern. Relativistic effects have also been discussed for gold [33]. Au-O bonds can be significantly strengthened by the linear O-Au-O structures.…”