Research reveals gas-phase migration route for formation of strong metal-support interaction state

Strong metal-support interaction (SMSI) is one of the most important concepts in heterogeneous catalysis. Triggered by pretreatment or reaction processes, the supported metal nanoparticles may be partially or completely encapsulated by support-derived overlayers, which impact the catalytic performance of supported metal catalysts. However, the formation mechanism of the SMSI state is still unclear.

Recently, a research team led by Prof. Fu Qiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) proposed a gas-phase migration route for the formation of SMSI. This work was published in Angewandte Chemie International Edition.

So far, two diffusion routes of the support-derived species onto the metal surface have been suggested, including interface alloying and surface migration.

In this work, the researchers placed ZnO particles and Cu/Al₂O₃ powders in a microreactor in a dual-bed mode (ZnO||Cu/Al₂O₃). By utilizing gas-phase migration of Zn species in CO₂/H₂ atmosphere (0.5% CO₂/H₂, 450°C), they found that a self-limited thin ZnO_x overlayer grew on the surface of Cu nanoparticles (Cu@ZnO_x) in the Cu/Al₂O₃ catalyst without excessive deposition and aggregation of ZnO_x species. Thus, they obtained an optimal number of ZnO_x-Cu interface sites, which enhanced the methanol synthesis activity.

Moreover, the researchers demonstrated that the formation of the self-limited Cu@ZnO_x encapsulation structure was due to the evaporation of Zn atoms from the ZnO particles, migration to the Cu/Al₂O₃ catalyst, and further deposition onto the Cu surface to form ZnO_x overlayers under the synergistic effect of reducing H₂ and oxidizing CO₂ components at the treatment temperature.

"Our work elucidates the high temperature redox atmosphere-induced gas-phase migration route to the formation of the encapsulation structure or the classic SMSI state," said Prof. Fu.