Abstract

The design and preparation of structures involving hierarchical porous systems have attracted interest due to their potential applications in heterogeneous catalysis. In this work, a series of micro/mesoporous composite materials was prepared from Beta zeolite (H-BEA), via a two-step recrystallization method, varying the initial alkaline concentration of the reaction medium (i.e., 0.2, 0.6, 1.2, and 1.8 M aqueous NaOH) generating the MM-02, MM-06, MM-12, and MM-18 samples, respectively. Several techniques, such as FT-IR, XRPD, 27Al MAS NMR, FESEM-EDX, TEM, and N2 physisorption, were used to study the structure, acidity, and texture of the resulting materials. The alkaline treatment at the lowest concentration led to a material practically preserving the total concentration of acid sites of the H-BEA precursor and resulting in a hierarchical porous structure having intracrystalline mesopores and the intrinsic microporosity of Beta zeolites (MM-02). Meanwhile, a Beta/MCM-41 composite possessing an interesting hierarchical pore system with a non-conventional N2 isotherm was synthesized using 0.6 M NaOH (MM-06). Besides, the use of stronger alkalinity induced the formation of materials characterized by a poor contribution of microporosity caused by zeolite degradation, but showing a significant mesoporous presence from MCM-41 (MM-12 and MM-18). Finally, exploration assays of Low-Density Polyethylene (LDPE) catalytic pyrolysis were performed on the rich-zeolite hierarchical materials with a sample-to-catalyst mass ratio of 1/7 at 550 degrees C. The MM-02 catalyst showed the best performance, yielding selectivity values of 51 and 37% to BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes) and alkanes, respectively, with suppression of polycyclic aromatic hydrocarbons (PAH) production.