Unravelling Surface Basicity and Bulk Morphology in N-doped 2D & 3D Carbon-based Materials for the Steam- and O2-Free Dehydrogenation Catalysis

The last years have witnessed a wonderful technological renaissance that has boosted the development of light-heterodoped carbon-based nanomaterials as metal-free systems for a number of key industrial catalytic transformations. With a styrene (ST) global demand approaching 25 million tons per year, the ethylbenzene (EB) dehydrogenation to ST is nowadays one of the most challenging processes at the core of polymer synthesis. The current technology for ST production is a highly energy-demanding process that uses a large amount of steam and it is typically promoted by a K-Fe2O3 catalyst (K-Fe) at temperatures between 580 and 630 °C. Despite the general process feasibility, K-Fe lists the classical disadvantages of metal-based heterogeneous catalysts: e.g. a drastic deactivation/passivation due to the rapid generation of "coke" deposits and metal leaching or structural collapse occurring under harsh operative conditions. Carbon-based systems as such or in the form of heterodoped materials are known to catalyze the direct dehydrogenation reaction (DDH) with superior performance in terms of activity and selectivity compared to K-Fe.1 However, some key issues related to the complex puzzle of their physicochemical and morphological properties still remain to be addressed.2 The role of the surface basicity in N-doped carbons on DDH selectivity and catalyst stability on stream still remains a matter of debate within the scientific community. In this contribution, we describe a class of microporous, N-doped 3D and 2D systems as catalysts with superior activity and stability in the steam- and oxygen-free DDH of EB to ST. Selected materials from this series (Covalent Triazine Frameworks - CTFs) have unambiguously shown superior activity and remarkable selectivity in the ST production compared with other carbon- and/or metal-based benchmark systems of the state-of-the-art.3 A control of their chemico-physical properties and composition has unveiled for the first time the role of the chemically accessible surface basicity as a key factor for the inhibition of the catalyst deactivation, typically caused by the formation of coke deposits. Such a result paves the way to the rational design of effective and stable catalytic materials for the process.