Researchers believe that the puzzle of catalytic gold has now been partially solved. Gold is able to catalyze an oxidation reaction by first oxidizing itself. A new study, which provides evidence for the existence of a gold oxide phase at room temperature and atmospheric pressure, helps researchers finally understand the oxidation mechanisms of catalytic gold nanoclusters under these conditions.
"Understanding the mechanisms is essential in order to design oxidation catalysts that can work properly in these reactions using the oxygen found in the air. Catalysts that function at low temperatures will be extremely important in the future in terms of energy efficiency," says researcher Karoliina Honkala from the University of Jyväskylä in Finland.
The researchers presented new evidence, derived from computational experiments, that supports the claim that nanoscale gold clusters are capable of completely cleaving the oxygen-oxygen bond through the existence of a new gold oxide phase that forms in the region of the cluster's perimeter. The researchers predict that this mechanism is the preferred one under moderate conditions of one atmospheric pressure and room temperature. The research findings were published in the scientific journal Angewandte Chemie.
In their study, the scientists exposed the monolayer-thick gold clusters to a varying number of oxygen atoms. It was found that even one gold cluster is able to efficiently absorb several oxygen species within the cluster boundaries, and simultaneously weaken the oxygen-oxygen bond by transferring electrons to them. Considering the temperature and pressure conditions of the reaction, the calculations predict that the oxygen atoms will completely dissolve and that the gold and oxygen atoms will form alternating one-dimensional chains (gold-oxygen-gold-oxygen, etc.) at the boundaries of the aggregate.
The oxygen atoms in these chains are negatively charged, while the gold atoms are positively charged, obtaining a system reminiscent of a one-dimensional chain of gold oxide. These chains are expected to be very catalytically active with respect to the conversion of carbon monoxide to carbon dioxide at room temperature. The researchers examined single-layer thick gold clusters containing 20-10 atoms, which are supported by thin layers of magnesium oxide prepared on metallic silver.
Comprehensive research conducted since the beginning of the XNUMXs showed that gold nanoparticles exhibit outstanding catalytic activity towards many chemical reactions that are important in industry and that involve the activation of the atomic bonds within oxygen or hydrocarbons. Obtaining carbon dioxide from carbon monoxide and separating oxygen at room temperature is one of the most studied processes. In these studies, several factors were proposed that could be responsible for the ability of the gold particles to activate the oxygen-oxygen bond, which is the key step in the reaction.
"The findings of the research that has just been published provide us with a new approach to solving the problem. The acceptance of gold oxide, that is - the oxidation of gold - stands in contradiction to the known properties of ordinary gold metal. In the nanometer world, it turns out, everything seems possible," says the researcher.
