Silanol Networks Control Methanol Reactivity in Nano- and Micron-sized Silicalite-1

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Silanol groups in zeolites were historically considered catalytically inactive due to low acidity.
• Brønsted acid sites were the primary focus for zeolite catalysis.

Purpose of the Study:

• To investigate the catalytic activity of silanol groups in pure silica MFI zeolite (Silicalite-1) during methanol conversion.
• To elucidate the role of silanol hydrogen bonding and crystal size on catalytic performance.

Main Methods:

• Synthesis of micron-sized (Sil1_micro) and nano-sized (Sil1_nano) Silicalite-1.
• In situ and operando FTIR spectroscopy with probe molecules (CO, pyridine, methanol).
• Multivariate curve regression (MCR-ALS) for data analysis.

Main Results:

• Silanol groups exhibit distinct acid-base behaviors influenced by hydrogen bonding and temperature.
• Weakly hydrogen-bonded silanols are active at low temperatures; strongly bonded ones at high temperatures.
• Nano-sized Silicalite-1 showed a unique methanol coordination mode, promoting reactive intermediates and dual coke species.

Conclusions:

• Silanol groups are active catalytic sites, not passive defects, in methanol conversion.
• Silanol hydrogen bonding network and crystal size significantly influence reactivity and coke formation pathways.
• Zeolite silanol activity is crucial for understanding methanol reforming-like transformations.