Dynamic Potassium Segregation Drives Cu²⁺ → Cu⁺ Transition and Redefines Alkali-Metal Promotion in Selective...

Area of Science:

• Heterogeneous Catalysis
• Surface Science
• Materials Chemistry

Background:

• Alkali-metal promoters, like potassium, are crucial in heterogeneous catalysis, often explained by electron donation to create active sites.
• However, potassium exists as electron-deficient K+ under reaction conditions, creating a paradox regarding its promotional effects, especially in CuO for propylene epoxidation.
• The conventional electronic picture fails to explain how potassium salts, not metallic K, induce Cu+ formation in CuO.

Purpose of the Study:

• To uncover the atomic-level origin of K+ promotion in the Cu-O-K system, specifically addressing the Cu2+ → Cu+ transition.
• To challenge the prevailing electron-donor paradigm by investigating the operando structural state of potassium.
• To elucidate the role of dynamic ionic segregation and surface restructuring in catalytic enhancement.

Main Methods:

• Development of a genetic-algorithm-driven active-learning workflow.
• Integration of neural network potentials and large-scale molecular dynamics simulations.
• Dynamic simulations of realistic 3 nm K+-modified CuO nanoparticles.

Main Results:

• K+ incorporated into the CuO lattice or statically on the surface is electronically inert; Cu2+ → Cu+ reduction stems from dynamic surface segregation of undercoordinated K+.
• Local lattice distortions induced by K+ segregation weaken Cu-O bonds, stabilizing reduced copper centers.
• Potassium segregation reshapes catalyst morphology, forming Cu+-rich domains and stabilizing active square-planar CuO surface motifs, enhancing propylene oxide production.

Conclusions:

• The study overturns the electron-donor paradigm for alkali-metal promotion in catalysis.
• A general structural origin, driven by dynamic ionic segregation and surface restructuring under reaction conditions, is established.
• Findings provide atomic-level insight into K+ promotion, crucial for designing efficient catalysts for selective propylene oxide production.