Efficient and stable dehydrogenation of ethylbenzene over vanadia supported on ultra-fine Al2O3 nanofibers with excellent physicochemical properties

The design and development of a highly efficient and stable catalyst for styrene (ST) obtained from ethylbenzene (EB) dehydrogenation reaction is urgently required because a commercial Fe–K-based catalyst often undergoes severe deactivation resulted from the active phase decomposition into inactive ferrite compound at high temperatures (>600 °C). Herein, ultra-fine Al 2 O 3 nanofibers which are further self-assembled to form uniform rod-like morphology (R–Al 2 O 3 ) were fabricated via a facile sol-gel strategy and further utilized as support to dispersing vanadium species (V/R–Al 2 O 3 ). The physicochemical properties of the samples were systematically characterized by XRD, Raman, SEM, TEM, H 2 -TPR, CO 2 -TPD, XPS, and 27 Al MAS NMR techniques. It is found that except that R–Al 2 O 3 support has the merits of a high specific surface area, lager pore volume, and uniform mesopore structure, the presence of the unsaturated pentacoordinate Al 3+ ions plays a pivotal role in better dispersing V active species, with the existence of the isolate and/or polymeric forms. As compared to V/C–Al 2 O 3 (commercial Al 2 O 3 as support), the V/R–Al 2 O 3 catalyst endows outperformed catalytic performances for oxidative dehydrogenation of ethylbenzene in the presence of CO 2 (OEBDH-CO 2 ). In which, the V/R–Al 2 O 3 catalyst gives a high EB catalytic activity and good stability without significant deactivation phenomenon being detected even after the third regeneration test. Such a result can be principally ascribed to that R–Al 2 O 3 support with excellent textural properties can better disperse V species so as to expose more active sites, which is beneficial for improving the conversion efficiency of EB. More importantly, keeping/regaining high valence state of V species in the V/R–Al 2 O 3 catalyst under CO 2 as a soft oxidant effectively promotes Mars-Van Krevelen redox cycle, further suppressing the catalyst deactivation. This work provides a rational design strategy for a high efficiency and stable dehydrogenation catalyst by optimizing the textural properties of Al 2 O 3 support and introducing the unsaturated pentacoordinate Al 3+ ions.