Understanding alkali metal promotion in hydrogenation catalysis through Strong Metal-Base Interaction

Area of Science:

• Heterogeneous catalysis
• Surface science
• Materials chemistry

Background:

• Alkali metals are common promoters in heterogeneous catalysis, enhancing catalyst performance.
• The exact mechanisms of alkali metal promotion, especially dynamic structural changes, are not fully understood.
• Understanding these interactions is crucial for designing advanced catalytic materials.

Purpose of the Study:

• To elucidate the promotional effect of alkali metals in hydrogenation reactions from a unified perspective.
• To introduce and define the Strong Metal-Base Interaction (SMBI) phenomenon.
• To demonstrate how SMBI can be used to control catalytic activity and selectivity.

Main Methods:

• Utilized a Na-doped Rh/TiO2 system as a representative model.
• Investigated the mechanism of H2 splitting facilitated by basic Na species.
• Analyzed the impact of Na doping on hydrogen spillover and electronic properties of Rh sites.
• Examined product selectivity in CO2, C=C, C=O, and N=O hydrogenation reactions.

Main Results:

• Demonstrated the Strong Metal-Base Interaction (SMBI) where basic Na species facilitate heterolytic H2 splitting.
• Observed suppressed hydrogen spillovers from Rh to TiO2 and electron-rich Rh sites due to SMBI.
• Showcased Na doping's ability to completely shift CO2 hydrogenation selectivity from CH4 to CO.
• Revealed enhanced C=C hydrogenation and suppressed C=O and N=O hydrogenation due to altered H adsorption and spillover.

Conclusions:

• SMBI provides a unified framework for understanding alkali metal promotion in hydrogenation.
• The interaction fundamentally alters catalytic behavior by modifying H2 splitting and spillover.
• This study offers a rational design strategy for developing efficient and selective hydrogenation catalysts.