Towards active macro–mesoporous hydrotreating catalysts: synthesis and assembly of mesoporous alumina microspheres
In this study, unique mesoporous structure alumina microspheres, each of which comprises an assembly of numerous highly crystallized alumina nanorods, were prepared via a facile template-free hydrothermal method. Such alumina microspheres were further assembled in one step to form a macroporous structure with abundant inter-microspheres via pore-directing-agent-free molding process. Owing to the morphological merits and the remarkable mechanical stability of the as-formed alumina microspheres, the macropores formed from the stable packing of the alumina microspheres had average sizes as large as 265 nm and were well connected with each other. Moreover, the inter-microsphere mesopores with an average size of 12.2 nm were well-maintained after the molding process. With such hierarchical porosity and large specific surface area, the as-prepared alumina support enabled better dispersion of the active MoNi components. Accordingly, the macro–mesoporous MoNi/Al2O3 catalyst exhibited both significantly higher catalytic activities and longer service life for the hydrodemetallization of nickel(II) 5, 10, 15, 20-tetraphenylporphine and for the hydrodesulfurization of dibenzothiophene as compared to controls with a single type of pores. With the ease of preparation, large surface area, and remarkable activity and stability, such a macro–mesoporous alumina support provides a promising alternative for hydrotreating heavy raw oils in industry.