Tailoring the preparation of USY zeolite with uniform mesoporosity for improved catalytic activity in phenol/isopropanol alkylation

Abstract

The preparation of hierarchical USY zeolite, exhibiting uniform mesoporosity and high Si/Al atomic ratio (48–52), has been investigated by means of a surfactant/ammonia post-treatment applied to a commercial USY sample. The procedure involved the use of temperatures within 40–135 °C, a low ammonia concentration solution (0.05 N) and hydrothermal synthesis times of 20 h. When working at 40–80 °C, the obtained USY samples exhibit enhanced intraparticular mesoporosity (324–418 m² g⁻¹), showing increasingly uniform mesopores around 4.0 nm, while holding a remarkable zeolitic microporosity (413–363 m² g⁻¹). In contrast, higher temperatures resulted in a steady abatement of crystalline zeolitic domains, with a total collapse of the zeolite structure at 135 °C. These hierarchical USY materials were tested in the alkylation of phenol with isopropanol, wherein one of the obtained products, e.g. 2,6-diisopropylphenol (Propofol), is the most important intravenous anaesthetic in the market. Interestingly, the generation of the uniform mesoporosity in USY samples led to an enhancement of both the phenol conversion and the selectivity towards C-alkylation products. Thus, the sample treated at 60 °C (USY-60) gave rise to the highest selectivity towards C-alkylation products (84 %) and poly-alkylphenols formation (72 %), with an encouraging selectivity towards 2,6-diisopropylphenol (43 %).