Structured Binder-Free Al-beta Zeolite for Acid-Catalyzed Dehydration

It has long remained a challenge in catalysis to synthesize technical hierarchical nanosized zeolites without growth modifiers and binders. Herein, we report a facile synthetic route to directly prepare binderless hierarchical Al-β zeolite in shaped form, with retained acidity, and sufficient mechanical strengths. The preparation process consists of two steps, where an Al-β zeolite nanopowder is first shaped using tetraethyl orthosilicate; the extrudate is then recrystallized under hydrothermal conditions with the assistance of tetraethylammonium hydroxide (TEAOH) solution. The alkaline environment leads to mesopores into the zeolite, and transforms as well the SiO2 binders into a zeolite framework. Several characterization methods were performed to reveal the structure-property relationships of the materials in powdered and shaped form. It was found that the process of TEAOH treatment is the combination of desilication, mesopore formation, and binder recrystallization to give zeolite Al-β nanoparticles, resulting in the obvious increase in microporosity, acidity, and X-ray diffraction crystallinity of samples. Density functional theory calculations were also used to rationalize the recrystallization process. Finally, the utility of the materials was demonstrated by evaluating their catalytic properties in the dehydration of 2-(4-ethylbenzoyl)-benzoic acid, a reaction which is traditionally catalyzed by concentrated sulfuric acid and oleum. We found that the catalyst in technical form exhibits better catalytic performance than the powdered HB nanoparticles and higher product yield than traditional (homogeneous) catalysts.