SO3H-containing functional carbon materials: Synthesis, structure, and acid catalysis

The "sulfonated carbons" are a new class of metal-free solid protonic acids characterized by their unique carbon structure and Bronsted acidity (-H₀ = 8-11) on par to concentrated H₂SO₄. These carbon materials covalently functionalized with SO₃H groups via C-PhSO₃H or C-SO₃H linkages can act as versatile water-tolerant solid acids. Due to their low production costs, unique surface chemistry, high chemical and thermal stability, as well as tailorable pore structures they are regarded as potential substitutes to liquid H₂SO₄. Catalysis, in particular, biomass and large molecule catalysis, is one of the important areas in which acidic carbons have demonstrated exceptional activity and selectivity, outperforming traditional solid acid catalysts (cation-exchange resins, sulfated oxides, and acidic zeolites). In this review we address developments in the different types SO₃H- and PhSO₃H-functionalized acidic carbon materials, their structure, active sites, and surface properties, applications in catalysis, as well as activation and deactivation characteristics covering important literature since 2004. In particular, we aim to provide a systematic discussion on the specific merits and demerits of such materials obtained from different carbon precursors and functionalization methods which directly influence the structure-stability-acidic properties and catalytic performance.