Modified natural halloysite nanotube solely employed as an efficient and low-cost solid acid catalyst for alpha-arylstyrenes production via direct alkenylation

• Modified halloysite can be solely employed as an efficient and low-cost solid acid.
• Alkenylation of aromcatics takes place smoothly over developed low-cost catalyst.
• The catalytic performance strongly depends on the acidic properties and pore structure.
• The appropriate acidic sites and their accessibility are essential for this reaction.
• Ion-exchange and calcination strongly affect the nature of modified catalyst.

Owing to unique mesoporous/macroporous hollow nanotubular structure, relatively high specific surface area, abundant surface hydroxyl groups, ecological and biocompatibility as well as low cost and large availability, the natural halloysite nanotube (HNT) has attracted great attention in drug delivery, catalysis, adsorption, energy storage, etc. HNT was generally used as support in catalysis, but rare report for HNT being solely used as catalyst. In this work, we firstly reported that HNTS were solely employed as a solid acid catalyst for alkenylation of diverse aromatics with phenylacetylene to their α-arylstyrenes. It was found that the HNT with a facile ion exchange and calcination pretreatment demonstrated outstanding catalytic performance in alkenylation of p-xylene with phenylacetylene, and 95.6% of phenylacetylene conversion with 95.8% of selectivity toward α-(2,5-dimenthylphenyl) styrene was achieved. The HNT were characterized by N2 physisorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), pyridine infrared spectroscopy (Py-IR), and Inductively coupled plasma (ICP), and thermogravimetric analysis (TGA) techniques. Correlated the nature of HNTs to reaction results, it was revealed that the catalytic performance of HNT was significantly dependent on their acidic properties and textural feature notably affected by ion exchange times (NIE) and calcination temperature (TC). Especially, besides acidic properties, the nature of the formed mesopores on the walls of HNTs strongly affects the catalytic activity, selectivity and coke-deposition behavior. The appropriate acidic sites and their accessibility are essential for obtaining satisfactory catalytic performance. The modified HNT catalyzed alkenylation can be extended to diverse substrates with good catalytic properties for diverse α-arylstyrenes production. The combination of excellent catalytic properties and the facile regeneration of deactivated HNT by calcination process allows it to be a promising candidate for, but limited to alkenylation of aromatics with phenylacetylene to their α-arylstyrenes.

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