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

It is a challenge to thoroughly understand the astonishing difference in catalytic activity between nanogold 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 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 nanogold 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.

Graphic abstract Strong relativistic effects strengthen Au–O bond by linear O–Au–O structures and weaken Au–O bond by neighboring gold atoms, which creates unique catalytic activity of nanogold catalysts.Figure optionsDownload as PowerPoint slide