Solid-state ³¹P NMR mapping of active centers and relevant spatial correlations in solid acid catalysts

Area of Science:

• Catalysis
• Materials Science
• Spectroscopy

Background:

• Solid acid catalysts are crucial in chemical and petrochemical industries.
• Catalyst performance hinges on acid site properties (type, location, concentration, strength, and spatial correlations).
• Characterizing these acid sites is essential for optimizing catalyst design and function.

Purpose of the Study:

• To present a comprehensive protocol for characterizing acid sites in solid acid catalysts using solid-state nuclear magnetic resonance (SSNMR).
• To detail the use of ³¹P probe molecules for qualitative and quantitative analysis of Brønsted and Lewis acid sites.
• To outline methods for NMR data acquisition, analysis, and mapping, including theoretical calculations.

Main Methods:

• ³¹P solid-state nuclear magnetic resonance (SSNMR) spectroscopy.
• Adsorption of trimethylphosphine (TMP) and trimethylphosphine oxide (TMPO) as ³¹P probe molecules.
• One- and two-dimensional (1D and 2D) NMR experiments, including ³¹P-¹H heteronuclear correlation (HETCOR), ³¹P-³¹P proton-driven spin diffusion (PDSD), and double-quantum (DQ) homonuclear correlation.
• Theoretical calculations for NMR mapping.

Main Results:

• The protocol enables detailed characterization of Brønsted and Lewis acid sites on solid catalysts.
• ³¹P probe molecules effectively adsorb to acid sites, providing valuable qualitative and quantitative data.
• Advanced NMR techniques allow for mapping and understanding the spatial correlations of acid sites.

Conclusions:

• ³¹P SSNMR is a powerful and reliable tool for characterizing solid acid catalysts.
• This protocol facilitates a deeper understanding of catalyst acidity, crucial for optimizing catalytic performance.
• The described methodology supports the advancement of catalyst design and application in various chemical processes.