Spatially Proximate Acid Sites in Zeolites Synergistically Boost Alkane Activation.

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Zeolite-catalyzed light alkane activation traditionally relies on strong Brønsted acid sites (BAS).
• This focus has limited the development of more efficient catalysts.
• Steamed ZSM-5 zeolites offer a new platform for exploring alternative activation mechanisms.

Purpose of the Study:

• To investigate the role of proximate acid-site cooperativity in light alkane activation on steamed ZSM-5 zeolites.
• To elucidate the mechanism by which cooperative acid sites enhance alkane adsorption and activation.
• To demonstrate a new strategy for designing zeolite catalysts by engineering the acid-site microenvironment.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• In situ Fourier-transform infrared (FTIR) spectroscopy with 2D correlation analysis.
• Density Functional Theory (DFT) calculations.

Main Results:

• Steamed ZSM-5 zeolites feature B2 sites (from partial hydrolysis of framework aluminum) that cooperate with neighboring classical BAS (B1).
• These proximate B1/B2 sites exhibit enhanced propane adsorption due to optimized van der Waals interactions.
• Cooperative acid sites synergistically activate propane, boosting conversion from 27.2% to 37.5%.

Conclusions:

• Alkane activation in zeolites can be driven by proximate acid-site cooperativity, not solely by isolated BAS strength.
• Engineering the zeolite microenvironment by creating cooperative acid sites is a promising strategy for catalyst design.
• This work reveals a novel mechanism for alkane activation, expanding the scope of zeolite catalysis research.