![]() ![]() Furthermore, it cannot distinguish aprotic acidic groups (lactones, carboxylic anhydrides) that can hydrolyze into –OH or –COOH in water or acid/base solutions and does not account for the porosity and material hydrophilicity/hydrophobicity (in the liquid phase) 16, 17, 25. Boehm titration 24, 25 assumes bases of different strength react with a specific type of OCFGs but is challenged when distinct chemical functions possess similar pK a values. ![]() Raman spectroscopy is promising to detect the crystal and molecular structure and very sensitive to the structural disorder of carbon but cannot distinguish OCFGs 23. ![]() ![]() Yet, surface functionalities may undergo consecutive transformations giving gas-phase products formed in situ during TPDE rather than being in the initial carbon structure 20, 21, 22. Temperature-programmed decomposition mass spectrometry (TPDE-MS) can detect OCFGs over a temperature range (500 to 1200 K). While diffuse reflectance IR spectroscopy (DRIFTS) can be applied, obtaining IR extinction coefficients is challenging 18, 19. Specifically, Fourier transform infrared spectroscopy (FTIR), often used to distinguish sites based on the vibrational frequency of the chemical bonds, is inapplicable, as IR photons are almost completely absorbed by carbons. The relative activity of each type of site is unknown.ĭeveloping OCFGs composition-function relationships remains elusive due to having many different sites and limitations on characterization stemming from challenges in using ultraviolet and visible light-based spectroscopic techniques on carbon 17. Furthermore, several OCFGs can serve as Brønsted acid sites (BAS), e.g., for dehydration, cellulose hydrolysis, etc 14, 15, 16., or base sites. It has been suggested that the composition in acidic OCFGs (–OH, –COOH, lactone, carboxylic anhydrides) affects the metal particle size distribution by serving as coordination sites for metal cations, greatly dispersing metal particles 13. Undoubtedly, oxygen-containing functional groups (OCFGs) are widely investigated in many applications 10, 11, 12. The microenvironment of carbon atoms 4, 6, 7, 8 strongly impacts the interaction between reactants, intermediates, and products with catalysts 9, 10. Functionalization with heteroatoms 4, 5, including N, O, P, etc., makes carbon a prominent support and a metal-free catalyst. Pure carbon with a uniform sp 2-hybridized structure is not suitable for catalysis. Owing to their low cost, light-weight, high surface area, high thermal conductivity, and readily modified structure and surface chemistries, carbon-based catalysts are routinely used for energy storage, sensors, electrocatalysis, and heterogeneous catalysis 1, 2, 3. The methodology can identify acidic sites in oxygenated carbon materials in solid acid catalyst-driven chemistry. By combining acid-catalyzed elimination probe chemistry, comprehensive surface characterizations, 15N isotopically labeled acetonitrile adsorption coupled with magic-angle spinning nuclear magnetic resonance, machine learning, and density-functional theory calculations, we demonstrate that phenolic is the main acid site in gas-phase chemistries and unexpectedly carboxylic groups are much less acidic than phenolic groups in the graphitized mesoporous carbon due to electron density delocalization induced by the aromatic rings of graphitic carbon. Here we investigate the role of Brønsted acidic oxygen-containing functional groups by synthesizing a diverse library of materials. However, distinguishing the role of various oxygen functional groups and quantifying and tuning each functionality is still difficult. Oxygen-containing carbons are promising supports and metal-free catalysts for many reactions. ![]()
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