Metal-free Functionalized Carbons in Catalysis: Synthesis, Characterization and Applications
Carbon-based materials show unique chemico-physical properties in their various allotropic forms and they have been successfully used in many catalytic processes including the production of chemicals and energy. Carbons have been traditionally used as supports for metals. However, carbon itself can act as a potential catalyst with recent pioneering studies showing it can replace the use of metals or metal-oxide-based catalysts in the gas phase oxidative dehydrogenation (ODH) of alkanes, such as ethylbenzene and alkenes. Metal-free carbons were successfully applied in several catalytic processes including photocatalysis, electrocatalysis, and liquid-phase oxidation processes. Compared to traditional metal-based catalysts, carbon materials have many advantages, such as their high surface area, unique electronic properties, high resistance to acids and alkalis, and thermal stability. In particular, the discovery of fullerene, carbon nanotubes, and graphene offered materials with higher activity and stability compared to classical carbon black and activated carbon. Their well-defined structures present great opportunities to advance the understanding of carbon materials chemistry. The catalytic activities of carbon materials are intimately related to their defects, structures, and surface chemistry. The introduction of defects and heteroatoms (N, B, P, S) alters the electronic properties of the surfaces, often increasing the reactivity of the surface of nanocarbons. The inclusion of hetero-elements in the honeycomb carbon structure induces a deep redistribution of the electronic properties. An ever-growing number of functionalized carbons (preferentially containing nitrogen) are nowadays employed with success as metal-free catalysts. Indeed, nitrogen-functionalized carbons present different surface functional groups, and they can be used as multifunctional catalysts, either through their electronic or nucleophilic properties, or ability to form additional H bonds with substrates. The scope of this book is to provide an overview of the preparation, characterization and application of metal-free functionalized carbons. The first three chapters will cover the preparation of the most common functionalized carbon utilized in metal-free catalysis, including carbon functionalized by covalent methods (Chapter 1) and non-covalent methods (Chapter 2). Chapter 3 provides an insight into the preparation of carbon nitrides (g-C3N4) and covalent triazine frameworks (CTF). Chapters 4 and 5 describe the most useful spectroscopy techniques to characterize the carbon surface, such as Raman, infrared spectroscopy, inelastic neutron scattering (INS) and X-ray photoelectron spectroscopy (XPS). The last part of the book provides a description of the different applications of metal-free functionalized carbon including liquid-phase reactions (Chapter 6), gas-phase reactions (Chapter 7), electrocatalysis (Chapter 8) and photocatalysis (Chapter 9). Finally, Chapter 10 describes the utilization of metal-free doped carbons for electroanalytical sensors. As editors, we believe that all the contents of this book constitute a valuable contribution to understanding the fundamental chemistry of metal-free carbon materials and will inspire both researchers already involved in the subject and those who would like to approach this field.