A new route for the synthesis of self-acidified and granulated mesoporous alumina catalyst with superior Lewis acidity and its application in cumene conversion

Abstract

Self-acidified and granulated mesoporous alumina (SAGMA) with dendritic-like microscopic shape was prepared by a new route that involves: (a) direct dehydration of AlCl3 (in the presence of capping petroleum wax), and (b) oxidation of intermediary AlCl3-nanorods. The AlCl3 solution dispersed in petroleum wax (capping media) was firstly dehydrated at 100 °C under inert atmosphere for manufacturing anhydrous AlCl3-nanorods (length: 50–100 nm; diameter: 5–10 nm). In a second step, this support was oxidized into γ-alumina at 300 °C, under air atmosphere. In the course of the manufacturing process, released chlorine was deposited at the surface of the nanorods (more specifically during the oxidation step). The binding of chlorine (5.35%, w/w at the surface) onto γ-alumina was demonstrated by both electron dispersive X-ray analysis (SEM–EDX) and Fourier-transformed infrared spectroscopy. Specific surface area reached 230 m2 g−1; the average pore size was 7.8 nm. Material characterization was completed by measuring the surface acidity through both temperature-programmed desorption and pyridine desorption. The morphology and the phase structure were investigated using scanning electron microscopy and X-ray diffraction analysis, respectively. SAGMA (γ-alumina) can be described as a strong Lewis (1.713 mmol g−1; i.e., about 93% of total acid sites) and Bronsted acid catalyst supported on a mesoporous structure (self-granular size of 177–250 µm). Cumene conversion (through a dealkylation pathway) was tested on SAGMA: maximum catalytic activity reached 87% at 300 °C. The conversion is highly selective: the reaction produces benzene and only traces of ethylbenzene (mass fraction below 4% compared to benzene). Apart from this good catalytic efficiency, the material is characterized by its strong stability in terms of both catalytic activity (loss less than 2%, for optimum conditions) and surface acidity (loss less than 3%), even for long reaction times (i.e., 24 h) under severe conditions (i.e., T 300 °C). This new material, easily manufactured, is characterized by high efficiency and selectivity in cumene conversion into benzene, associated with high acidity and good stability.