Unraveling surface basicity and bulk morphology on metal-free C-based catalysts with unique dehydrogenation performance

The high chemical versatility together with the unique chemico-physical properties of carbon-based nanomaterials (CNMs) have opened wide horizons in key sectors of functional materials basic research and heterogeneous catalysis. In particular, CNMs doped with light-heteroelements and featured by hierarchical porous architectures have been studied as unique catalytic materials for promoting a number of key industrial transformations. On this ground, the steam- and oxygen-free direct dehydrogenation (DDH) of Ethylbenzene (EB) to Styrene (ST) represents one of the most important industrial processes at the heart of polymer synthesis where activity and selectivity represent two significant features. The catalyst stability under harsh operative conditions, the reduction of leaching of its active sites and their resistance to deactivation phenomena on stream are key parameters to be kept in mind while designing and synthesizing new catalytic materials for the process. The current industrial technology for ST production is a highly energy-demanding process typically promoted by a K-Fe2O3 catalyst (K-Fe) at temperatures between 580 and 630 °C with the use of a large amount of steam. Despite the general process feasibility, K-Fe lists the classical disadvantages of metal-based heterogeneous catalysts: a drastic deactivation/passivation due to the rapid generation of "coke" deposits and metal leaching or structural collapse occurring under severe operative conditions. Carbon-based catalysts have recently emerged as valuable metal-free catalysts for DDH, offering superior performance in terms of activity and selectivity compared to the K-Fe system. However, from the viewpoint of developing effective and sustainable metal-free catalysts for the DDH process, some key issues related to the complex puzzle of physicochemical and morphological properties of CNMs still remain to be addressed. In particular, the role of the surface basicity in Ndoped carbons on the DDH selectivity and catalyst stability on stream, remains a matter of debate among the scientific community. This contribution sheds light on this tricky matter revealing complex structure-reactivity relationships of a class of highly microporous, N-rich Covalent Triazine Frameworks with superior activity and stability in DDH compared to the benchmark metal-based and metal-free systems of the state-of-the-art, particularly at harsh operative conditions close to those used in industrial plants.