In the field of heterogeneous catalysis, the atomically dispersed metal catalyst has attracted great attention due to their unique geometric and electronic properties, the highest atom efficiency, and uniform active sites. However, the highly dispersed metal atoms either move and agglomerate easily because of high surface energy, resulting in low stability, or strongly interact with the support and become catalytically passivated. Therefore, how to obtain "moving but not agglomerating" metal sites that can enhance both catalytic activity and stability has always been a tough spot in catalysis.
Given this, the research team designed a new type of "nanoisland" catalyst (also called nanoglue), in which active metal atoms are isolated on "islands" where they can move within respectively, but the migration to neighboring "islands" is suppressed, consequently obtaining "moving but not agglomerating" atom sites.
To achieve this goal, appropriate materials need to be chosen for "nanoislands" and the supports, respectively. The affinity between metal atoms and "nanoislands" should be much stronger than that between metal atoms and support. Otherwise, the metal atoms are easy to leave their own "nanoislands". Therefore, the researchers chose oxides with high affinity to metal atoms as "islands" (such as ceria) in the designed model catalyst, and weak-interaction oxides (such as silica) as support to stabilize "islands".
To efficiently isolate metal atoms, the "islands" should be of small enough size and high enough number density on support. The conventional synthesis methods (such as the impregnation method) tend to obtain large and non-uniform particles which are not suitable as "islands". So the team developed a strong electrostatic adsorption method in an aqueous solution. The high-density cerium atoms were firstly coated to silica surface, then they agglomerated into isolated "islands" with a size less than two nanometers through calcination.
